Showing 1–50 of 64 results for author: Vujanovic, G

Characterizing the initial state of hydrodynamics in pp and pA collisions

Authors: Gabriel Rabelo-Soares, Gojko Vujanovic, Giorgio Torrieri

Abstract: The observation of seeming hydrodynamic-like behavior in proton-proton and proton-nucleus collisions presents us with the conceptual problem of how the initial state of such a hydrodynamic evolution should be characterized. This is an issue because, while nuclei can reasonably be approximated as ``large'' systems w.r.t. the characteristic Fermi momentum of their constituents, this is no longer tru… ▽ More The observation of seeming hydrodynamic-like behavior in proton-proton and proton-nucleus collisions presents us with the conceptual problem of how the initial state of such a hydrodynamic evolution should be characterized. This is an issue because, while nuclei can reasonably be approximated as ``large'' systems w.r.t. the characteristic Fermi momentum of their constituents, this is no longer true for nucleons. Hence, one would need to match a ``quantum'' theory, whose observables are described via highly non-commuting operators, to a ``classical'' hydrodynamics. Operationally assuming a ``fast'' thermalization, we survey what kind of object is best suited to such a matching condition. We show that it cannot be any of the objects usually associated with ``the 3D structure of the nucleon'' but rather a measure associated with entanglement entropy. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: Comments are welcome!

Transport-based initial conditions for heavy-ion collisions at finite densities

Authors: H. Roch, G. Pihan, A. Monnai, S. Ryu, N. Senthilkumar, J. Staudenmaier, H. Elfner, B. Schenke, J. H. Putschke, C. Shen, S. A. Bass, M. Chartier, Y. Chen, R. Datta, R. Dolan, L. Du, R. Ehlers, R. J. Fries, C. Gale, D. A. Hangal, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, F. Jonas , et al. (31 additional authors not shown)

Abstract: We employ the SMASH transport model to provide event-by-event initial conditions for the energy-momentum tensor and conserved charge currents in hydrodynamic simulations of relativistic heavy-ion collisions. We study the fluctuations and dynamical evolution of three conserved charge currents (net baryon, net electric charges, and net strangeness) with a 4D lattice-QCD-based equation of state, NEOS… ▽ More We employ the SMASH transport model to provide event-by-event initial conditions for the energy-momentum tensor and conserved charge currents in hydrodynamic simulations of relativistic heavy-ion collisions. We study the fluctuations and dynamical evolution of three conserved charge currents (net baryon, net electric charges, and net strangeness) with a 4D lattice-QCD-based equation of state, NEOS-4D, in the hydrodynamic phase. Out-of-equilibrium corrections at the particlization are generalized to finite densities to ensure the conservation of energy, momentum, and the three types of charges. These theoretical developments are integrated within X-SCAPE as a unified framework for studying the nuclear matter properties in the Beam Energy Scan program. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Comments: 16 pages, 12 figures

Glauber quark and gluon contributions to quark energy loss at next-to-leading order and next-to-leading twist

Authors: Amit Kumar, Gojko Vujanovic

Abstract: The higher-twist (HT) formalism is used at $O(α^2_s)$ to compute all possible medium-induced single-scattering emission kernels for an incoming highly energetic and virtual quark traversing the nuclear environment. The effects of the heavy-quark mass scale are taken into account [Phys. Rev. C 94, 054902 (2016)] both in the initial state as well as in the final state, along with interactions involv… ▽ More The higher-twist (HT) formalism is used at $O(α^2_s)$ to compute all possible medium-induced single-scattering emission kernels for an incoming highly energetic and virtual quark traversing the nuclear environment. The effects of the heavy-quark mass scale are taken into account [Phys. Rev. C 94, 054902 (2016)] both in the initial state as well as in the final state, along with interactions involving both in-medium Glauber gluons and quarks [Nucl. Phys. A 793, 128 (2007)], as well as coherence effects [Phys. Rev. C 105, 024908 (2022)]. As this study is a continuation of our work on medium-induced photon production [Phys. Rev. C 112, 025204 (2025)], the general factorization procedure for $e$-$A$ deep-inelastic scattering is still used. An incoming quark energy loss in the nuclear medium yields four possible scattering kernels $K_i$ with the following final states: (i) $q+g$, (ii) $g+g$, (iii) $q+\bar{q}'$, where the quark $q$ may have a flavor different from the antiquark $\bar{q}'$, and (iv) $q+q'$, where, again, $q$ may have a flavor different from $q'$. The collisional kernels include full phase factors from all non-vanishing diagrams and complete first-order derivative in the longitudinal direction ($k^-$) as well as second-order derivative in the transverse momentum ($k_{\perp}$) gradient expansion. Furthermore, in-medium parton distribution functions and the related jet transport coefficients have a hard transverse-momentum dependence (of the emitted quark or gluon) present within the phase factor. △ Less

Submitted 26 September, 2025; v1 submitted 12 September, 2025; originally announced September 2025.

Comments: 64 pages, 23 figures;

Interplay of prompt and non-prompt photons in photon-triggered jet observables

Authors: Chathuranga Sirimanna, Yasuki Tachibana, Abhijit Majumder, Aaron Angerami, Ritu Arora, Steffen Bass, Yi Chen, Ritoban Datta, Lipei Du, Raymond Ehlers, Hannah Elfner, Rainer J. Fries, Charles Gale, Yayun He, Barbara Jacak, Peter Jacobs, Sangyong Jeon, Yi Ji, Florian Jonas, Lauren Kasper, Michael Kordell, Amit Kumar, Raghav Kunnawalkam-Elayavalli, Joseph Latessa, Yen-Jie Lee , et al. (27 additional authors not shown)

Abstract: Prompt photons are important yet challenging to observe in relativistic heavy-ion collisions, as they are produced in the early stages and traverse almost the entire QGP medium without interaction. Experimental analyses typically employ isolation cuts, in the hope to identify prompt photons. Most theoretical studies consider only events with actual prompt photons, assuming no contribution from iso… ▽ More Prompt photons are important yet challenging to observe in relativistic heavy-ion collisions, as they are produced in the early stages and traverse almost the entire QGP medium without interaction. Experimental analyses typically employ isolation cuts, in the hope to identify prompt photons. Most theoretical studies consider only events with actual prompt photons, assuming no contribution from isolated non-prompt photons to reduce computational cost. For the first time, we present a study that compares simulation results generated using inclusive (bremsstrahlung) and prompt-photon events with multiple experimental observables for both $p-p$ and $Pb-Pb$ collisions at $5.02$ TeV. Simulations are carried out using the multi-stage JETSCAPE framework tuned to describe the quenching of jets and hadrons. Isolated non-prompt photons are generated in hard photon bremsstrahlung, where the photon is radiated at a sufficient angle to the jet. Several photon triggered jet and jet substructure observables show significant contributions from inclusive photons, yielding an improvement in comparison with experimental data. Novel photon triggered jet substructure observables are also expected to show new structures, yet to be detected in experiment. This effort examines the significance of isolated non-prompt photons using parameters tuned for a simultaneous description of the leading hadron and jet spectrum, and thus provides an independent verification of the multistage evolution framework. △ Less

Submitted 1 July, 2025; originally announced July 2025.

Comments: 5 pages, 4 figures

Effects of hadronic reinteraction on jet fragmentation from small to large systems

Authors: Hendrik Roch, Aaron Angerami, Ritu Arora, Steffen Bass, Yi Chen, Ritoban Datta, Lipei Du, Raymond Ehlers, Hannah Elfner, Rainer J. Fries, Charles Gale, Yayun He, Barbara Jacak, Peter Jacobs, Sangyong Jeon, Yi Ji, Florian Jonas, Lauren Kasper, Michael Kordell II, Amit Kumar, Raghav Kunnawalkam-Elayavalli, Joseph Latessa, Yen-Jie Lee, Roy Lemmon, Matt Luzum , et al. (27 additional authors not shown)

Abstract: We investigate the impact of the hadronic phase on jet quenching in nuclear collider experiments, an open question in heavy-ion physics. Previous studies in a simplified setup suggest that hadronic interactions could have significant effects, but a systematic analysis is needed. Using the X-SCAPE event generator with the SMASH afterburner, we study the role of hadronic rescattering on jet fragment… ▽ More We investigate the impact of the hadronic phase on jet quenching in nuclear collider experiments, an open question in heavy-ion physics. Previous studies in a simplified setup suggest that hadronic interactions could have significant effects, but a systematic analysis is needed. Using the X-SCAPE event generator with the SMASH afterburner, we study the role of hadronic rescattering on jet fragmentation hadrons. Applying this framework to $e^++e^-$ collisions, we demonstrate that even in small systems with limited particle production, hadronic interactions lead to measurable modifications in final-state hadronic and jet observables by comparing scenarios with and without afterburner rescattering. △ Less

Submitted 19 June, 2025; originally announced June 2025.

Comments: 6 pages, 3 figures, conference proceedings for Hard Probes 2024

Extraction of jet-medium interaction details through jet substructure for inclusive and gamma-tagged jets

Authors: Y. Tachibana, C. Sirimanna, A. Majumder, A. Angerami, R. Arora, S. A. Bass, Y. Chen, R. Datta, L. Du, R. Ehlers, H. Elfner, R. J. Fries, C. Gale, Y. He, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, F. Jonas, L. Kasper, M. Kordell II, A. Kumar, R. Kunnawalkam-Elayavalli, J. Latessa, Y. -J. Lee , et al. (27 additional authors not shown)

Abstract: We present a comprehensive study of jet substructure modifications in high-energy heavy-ion collisions using both inclusive jets and $γ$-tagged jets, based on a multi-stage jet evolution model within the Monte Carlo framework JETSCAPE. To investigate hard parton splittings inside jets, we focus on Soft Drop observables. Our results for the groomed splitting radius and groomed jet mass distribution… ▽ More We present a comprehensive study of jet substructure modifications in high-energy heavy-ion collisions using both inclusive jets and $γ$-tagged jets, based on a multi-stage jet evolution model within the Monte Carlo framework JETSCAPE. To investigate hard parton splittings inside jets, we focus on Soft Drop observables. Our results for the groomed splitting radius and groomed jet mass distributions of inclusive jets show a slight narrowing compared to proton-proton baselines. We demonstrate that this apparent narrowing is primarily a selection bias from energy loss, rather than a direct modification of the splitting structure, by analyzing $γ$-tagged jets, where such bias is eliminated or significantly reduced. We also show that quark jets exhibit genuine modifications in their splitting structure, which is not seen in gluon jets. These effects are clearly visible in the substructure of $γ$-tagged jets, which are dominated by quark jets, but are not apparent for inclusive jets. This demonstrates that $γ$-tagged jets offer a powerful probe of medium-induced modifications to the hard splitting structure of jets. △ Less

Submitted 18 June, 2025; originally announced June 2025.

Comments: 5 pages, 3 figures, Proceedings of the 12th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2024), September 22-27, 2024, Nagasaki, Japan

Enhanced signal of momentum broadening in hard splittings for $γ$-tagged jets in a multistage approach

Authors: Y. Tachibana, C. Sirimanna, A. Majumder, A. Angerami, R. Arora, S. A. Bass, Y. Chen, R. Datta, L. Du, R. Ehlers, H. Elfner, R. J. Fries, C. Gale, Y. He, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, F. Jonas, L. Kasper, M. Kordell II, A. Kumar, R. Kunnawalkam-Elayavalli, J. Latessa, Y. -J. Lee , et al. (27 additional authors not shown)

Abstract: We investigate medium-induced modifications to jet substructure observables that characterize hard splitting patterns in central Pb-Pb collisions at the top energy of the Large Hadron Collider (LHC). Using a multistage Monte Carlo simulation of in-medium jet shower evolution, we explore flavor-dependent medium effects through simulations of inclusive and $γ$-tagged jets. The results show that quar… ▽ More We investigate medium-induced modifications to jet substructure observables that characterize hard splitting patterns in central Pb-Pb collisions at the top energy of the Large Hadron Collider (LHC). Using a multistage Monte Carlo simulation of in-medium jet shower evolution, we explore flavor-dependent medium effects through simulations of inclusive and $γ$-tagged jets. The results show that quark jets undergo a non-monotonic modification compared to gluon jets in observables such as the Pb-Pb to $p$-$p$ ratio of the Soft Drop prong angle $r_g$, the relative prong transverse momentum $k_{T,g}$ and the groomed mass $m_g$ distributions. Due to this non-monotonic modification, $γ$-tagged jets, enriched in quark jets, provide surprisingly clear signals of medium-induced structural modifications, distinct from effects dominated by selection bias. This work highlights the potential of hard substructures in $γ$-tagged jets as powerful tools for probing the jet-medium interactions in high-energy heavy-ion collisions. All simulations for $γ$-tagged jet analyses carried out in this paper used triggered events containing at least one hard photon, which highlights the utility of these observables for future Bayesian analysis. △ Less

Submitted 30 March, 2025; originally announced March 2025.

Comments: 26 pages, 31 figures

Bremsstrahlung photon contributions to parton energy loss at high virtuality ($Q^2$) : a perturbative calculation at $O(α_{s} α_{em})$

Authors: Amit Kumar, Gojko Vujanovic

Abstract: In this work, real photon production scattering kernels from jet-medium interactions in the QCD medium are perturbatively calculated using the higher-twist (HT) formalism. Focus is given towards real photon production from a highly virtual (and highly energetic) quark, taking into account heavy-quark mass scales [Phys. Rev. C 94, 054902 (2016)], fermion-boson conversion processes [Nucl. Phys. A 79… ▽ More In this work, real photon production scattering kernels from jet-medium interactions in the QCD medium are perturbatively calculated using the higher-twist (HT) formalism. Focus is given towards real photon production from a highly virtual (and highly energetic) quark, taking into account heavy-quark mass scales [Phys. Rev. C 94, 054902 (2016)], fermion-boson conversion processes [Nucl. Phys. A 793, 128 (2007)], as well as coherence effects [Phys. Rev. C 105, 024908 (2022)]. A generalized factorization procedure, such as that used in e-A deep-inelastic scattering, is employed to derive an improved single-scattering medium-induced photon emission kernels that go beyond the traditional in-medium gluon exchange approximation. Diagrams with real-photon emission from the hard quark are classified based on the final-state particles, and include two types of scattering kernels at $O(α_{em}α_{s})$ giving the following final states: (i) real photon and real quark, (ii) real photon and real gluon. The collisional kernels, thus derived, include full phase factors from all non-vanishing diagrams and complete second-order derivative terms in the transverse momentum gradient expansion. Moreover, the calculation includes heavy-quark mass effects, thus exploring heavy-quark energy loss. The in-medium parton distribution functions and the related jet transport coefficients have a hard transverse momentum dependence (of the emitted gluon or photon) present within the phase factor. It is observed that the jet transport coefficients resemble the transverse-momentum-dependent parton distribution functions. △ Less

Submitted 8 September, 2025; v1 submitted 4 February, 2025; originally announced February 2025.

Comments: Published version, 48 pages, 25 figures;

Journal ref: Phys. Rev. C 112, 025204 (2025)

Hybrid Hadronization -- A Study of In-Medium Hadronization of Jets

Authors: A. Sengupta, R. J. Fries, M. Kordell II, B. Kim, A. Angerami, R. Arora, S. A. Bass, Y. Chen, R. Datta, L. Du, R. Ehlers, H. Elfner, C. Gale, Y. He, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, F. Jonas, L. Kasper, A. Kumar, R. Kunnawalkam-Elayavalli, J. Latessa, Y. -J. Lee, R. Lemmon , et al. (28 additional authors not shown)

Abstract: QCD jets are considered important probes for quark gluon plasma created in collisions of nuclei at high energies. Their parton showers are significantly altered if they develop inside of a deconfined medium. Hadronization of jets is also thought to be affected by the presence of quarks and gluons. We present a systematic study of the effects of a thermal bath of partons on the hadronization of par… ▽ More QCD jets are considered important probes for quark gluon plasma created in collisions of nuclei at high energies. Their parton showers are significantly altered if they develop inside of a deconfined medium. Hadronization of jets is also thought to be affected by the presence of quarks and gluons. We present a systematic study of the effects of a thermal bath of partons on the hadronization of parton showers. We use the JETSCAPE framework to create parton showers both in vacuum and in a brick of quark gluon plasma. The brick setup allows important parameters, like the size of the plasma as well as the collective flow of partons, to be varied systematically. We hadronize the parton showers using Hybrid Hadronization, which permits shower partons to form strings with thermal partons, or to recombine directly with thermal partons as well as with each other. We find a sizeable amount of interaction of shower partons with thermal partons during hadronization, indicating a natural continuation of the interaction of jet and medium during this stage. The observed effects grow with the size of the medium. Collective flow easily transfers from the thermal partons onto the emerging jet hadrons. We also see a significant change in hadron chemistry as expected in the presence of quark recombination processes. △ Less

Submitted 27 January, 2025; originally announced January 2025.

Comments: 12 pages, 6 figures

White Paper on Software Infrastructure for Advanced Nuclear Physics Computing

Authors: P. M. Jacobs, A. Boehnlein, B. Sawatzky, J. Carlson, I. Cloet, M. Diefenthaler, R. G. Edwards, K. Godbey, W. R. Hix, K. Orginos, T. Papenbrock, M. Ploskon, C. Ratti, R. Soltz, T. Wenaus, L. Andreoli, J. Brodsky, D. Brown, A. Bulgac, G. D. Chung, S. J. Coleman, J. Detwiler, A. Dubey, R. Ehlers, S. Gandolfi , et al. (27 additional authors not shown)

Abstract: This White Paper documents the discussion and consensus conclusions of the workshop "Software Infrastructure for Advanced Nuclear Physics Computing" (SANPC 24), which was held at Jefferson Lab on June 20-22, 2024. The workshop brought together members of the US Nuclear Physics community with data scientists and funding agency representatives, to discuss the challenges and opportunities in advanced… ▽ More This White Paper documents the discussion and consensus conclusions of the workshop "Software Infrastructure for Advanced Nuclear Physics Computing" (SANPC 24), which was held at Jefferson Lab on June 20-22, 2024. The workshop brought together members of the US Nuclear Physics community with data scientists and funding agency representatives, to discuss the challenges and opportunities in advanced computing for Nuclear Physics in the coming decade. Opportunities for sustainable support and growth are identified, within the context of existing and currently planned DOE and NSF programs. △ Less

Submitted 21 April, 2025; v1 submitted 1 January, 2025; originally announced January 2025.

Comments: Final version

Hard Photon Triggered Jets in $p$-$p$ and $A$-$A$ Collisions

Authors: C. Sirimanna, Y. Tachibana, A. Majumder, A. Angerami, R. Arora, S. A. Bass, Y. Chen, R. Datta, L. Du, R. Ehlers, H. Elfner, R. J. Fries, C. Gale, Y. He, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, F. Jonas, L. Kasper, M. Kordell II, A. Kumar, R. Kunnawalkam-Elayavalli, J. Latessa, Y. -J. Lee , et al. (27 additional authors not shown)

Abstract: An investigation of high transverse momentum (high-$p_T$) photon triggered jets in proton-proton ($p$-$p$) and ion-ion ($A$-$A$) collisions at $\sqrt{s_{NN}} = 0.2$ and $5.02~\mathrm{TeV}$ is carried out, using the multistage description of in-medium jet evolution. Monte Carlo simulations of hard scattering and energy loss in heavy-ion collisions are performed using parameters tuned in a previous… ▽ More An investigation of high transverse momentum (high-$p_T$) photon triggered jets in proton-proton ($p$-$p$) and ion-ion ($A$-$A$) collisions at $\sqrt{s_{NN}} = 0.2$ and $5.02~\mathrm{TeV}$ is carried out, using the multistage description of in-medium jet evolution. Monte Carlo simulations of hard scattering and energy loss in heavy-ion collisions are performed using parameters tuned in a previous study of the nuclear modification factor ($R_{AA}$) for inclusive jets and high-$p_T$ hadrons. We obtain a good reproduction of the experimental data for photon triggered jet $R_{AA}$, as measured by the ATLAS detector, the distribution of the ratio of jet to photon $p_T$ ($X_{\rm J γ}$), measured by both CMS and ATLAS, and the photon-jet azimuthal correlation as measured by CMS. We obtain a moderate description of the photon triggered jet $I_{AA}$, as measured by STAR. A noticeable improvement in the comparison is observed when one goes beyond prompt photons and includes bremsstrahlung and decay photons, revealing their significance in certain kinematic regions, particularly at $X_{Jγ} > 1$. Moreover, azimuthal angle correlations demonstrate a notable impact of non-prompt photons on the distribution, emphasizing their role in accurately describing experimental results. This work highlights the success of the multistage model of jet modification to straightforwardly predict (this set of) photon triggered jet observables. This comparison, along with the role played by non-prompt photons, has important consequences on the inclusion of such observables in a future Bayesian analysis. △ Less

Submitted 27 December, 2024; originally announced December 2024.

Comments: 16 pages, 10 figures

Electromagnetic Probes of the Quantum Chromodynamical Plasma

Authors: Gojko Vujanovic

Abstract: In relativistic heavy-ion collisions, electromagnetic (EM) radiation has been used as a sensitive probe of Quark Gluon Plasma (QGP) properties, owing to the smaller EM coupling relative to QCD coupling. To better understand the constraining power of EM emissions on transport properties of the QGP, a deeper understanding of both the theory and phenomenology of EM signals is required. A selection of… ▽ More In relativistic heavy-ion collisions, electromagnetic (EM) radiation has been used as a sensitive probe of Quark Gluon Plasma (QGP) properties, owing to the smaller EM coupling relative to QCD coupling. To better understand the constraining power of EM emissions on transport properties of the QGP, a deeper understanding of both the theory and phenomenology of EM signals is required. A selection of recent developments in those two areas of QGP EM probes is discussed, with an outlook on how Bayesian model-to-data comparisons can help further quantify our understanding of QGP transport coefficients. △ Less

Submitted 25 April, 2025; v1 submitted 29 November, 2024; originally announced November 2024.

Comments: 6 pages, Proceedings for the 14th International Conference on Nucleus-Nucleus Collisions (NN2024), Whistler, British Columbia, Canada, August 18-23, 2024

Bayesian Inference analysis of jet quenching using inclusive jet and hadron suppression measurements

Authors: R. Ehlers, Y. Chen, J. Mulligan, Y. Ji, A. Kumar, S. Mak, P. M. Jacobs, A. Majumder, A. Angerami, R. Arora, S. A. Bass, R. Datta, L. Du, H. Elfner, R. J. Fries, C. Gale, Y. He, B. V. Jacak, S. Jeon, F. Jonas, L. Kasper, M. Kordell II, R. Kunnawalkam-Elayavalli, J. Latessa, Y. -J. Lee , et al. (28 additional authors not shown)

Abstract: The JETSCAPE Collaboration reports a new determination of the jet transport parameter $\hat{q}$ in the Quark-Gluon Plasma (QGP) using Bayesian Inference, incorporating all available inclusive hadron and jet yield suppression data measured in heavy-ion collisions at RHIC and the LHC. This multi-observable analysis extends the previously published JETSCAPE Bayesian Inference determination of… ▽ More The JETSCAPE Collaboration reports a new determination of the jet transport parameter $\hat{q}$ in the Quark-Gluon Plasma (QGP) using Bayesian Inference, incorporating all available inclusive hadron and jet yield suppression data measured in heavy-ion collisions at RHIC and the LHC. This multi-observable analysis extends the previously published JETSCAPE Bayesian Inference determination of $\hat{q}$, which was based solely on a selection of inclusive hadron suppression data. JETSCAPE is a modular framework incorporating detailed dynamical models of QGP formation and evolution, and jet propagation and interaction in the QGP. Virtuality-dependent partonic energy loss in the QGP is modeled as a thermalized weakly-coupled plasma, with parameters determined from Bayesian calibration using soft-sector observables. This Bayesian calibration of $\hat{q}$ utilizes Active Learning, a machine--learning approach, for efficient exploitation of computing resources. The experimental data included in this analysis span a broad range in collision energy and centrality, and in transverse momentum. In order to explore the systematic dependence of the extracted parameter posterior distributions, several different calibrations are reported, based on combined jet and hadron data; on jet or hadron data separately; and on restricted kinematic or centrality ranges of the jet and hadron data. Tension is observed in comparison of these variations, providing new insights into the physics of jet transport in the QGP and its theoretical formulation. △ Less

Submitted 28 August, 2024; v1 submitted 15 August, 2024; originally announced August 2024.

Comments: 20 pages, 10 figures, 2 tables, submitted to PRC; updated acknowledgements

A soft-hard framework with exact four momentum conservation for small systems

Authors: I. Soudi, W. Zhao, A. Majumder, C. Shen, J. H. Putschke, B. Boudreaux, A. Angerami, R. Arora, S. A. Bass, Y. Chen, R. Datta, L. Du, R. Ehlers, H. Elfner, R. J. Fries, C. Gale, Y. He, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, M. Kelsey, M. Kordell II, A. Kumar , et al. (28 additional authors not shown)

Abstract: A new framework, called x-scape, for the combined study of both hard and soft transverse momentum sectors in high energy proton-proton ($p$-$p$) and proton-nucleus ($p$-$A$) collisions is set up. A dynamical initial state is set up using the 3d-Glauber model with transverse locations of hotspots within each incoming nucleon. A hard scattering that emanates from two colliding hotspots is carried ou… ▽ More A new framework, called x-scape, for the combined study of both hard and soft transverse momentum sectors in high energy proton-proton ($p$-$p$) and proton-nucleus ($p$-$A$) collisions is set up. A dynamical initial state is set up using the 3d-Glauber model with transverse locations of hotspots within each incoming nucleon. A hard scattering that emanates from two colliding hotspots is carried out using the Pythia generator. Initial state radiation from the incoming hard partons is carried out in a new module called I-matter, which includes the longitudinal location of initial splits. The energy-momentum of both the initial hard partons and their associated beam remnants is removed from the hot spots, depleting the energy-momentum available for the formation of the bulk medium. Outgoing showers are simulated using the matter generator, and results are presented for both cases, allowing for and not allowing for energy loss. First comparisons between this hard-soft model and single inclusive hadron and jet data from $p$-$p$ and minimum bias $p$-$Pb$ collisions are presented. Single hadron spectra in $p$-$p$ are used to carry out a limited (in number of parameters) Bayesian calibration of the model. Fair comparisons with data are indicative of the utility of this new framework. Theoretical studies of the correlation between jet $p_T$ and event activity at mid and forward rapidity are carried out. △ Less

Submitted 24 July, 2024; originally announced July 2024.

Comments: 18 pages, 15 figures

Photon-triggered jets as probes of multi-stage jet modification

Authors: C. Sirimanna, Y. Tachibana, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, L. Du, R. Ehlers, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, M. Kordell II, A. Kumar, R. Kunnawalkam-Elayavalli, J. Latessa, S. Lee , et al. (28 additional authors not shown)

Abstract: Prompt photons are created in the early stages of heavy ion collisions and traverse the QGP medium without any interaction. Therefore, photon-triggered jets can be used to study the jet quenching in the QGP medium. In this work, photon-triggered jets are studied through different jet and jet substructure observables for different collision systems and energies using the JETSCAPE framework. Since t… ▽ More Prompt photons are created in the early stages of heavy ion collisions and traverse the QGP medium without any interaction. Therefore, photon-triggered jets can be used to study the jet quenching in the QGP medium. In this work, photon-triggered jets are studied through different jet and jet substructure observables for different collision systems and energies using the JETSCAPE framework. Since the multistage evolution used in the JETSCAPE framework is adequate to describe a wide range of experimental observables simultaneously using the same parameter tune, we use the same parameters tuned for jet and leading hadron studies. The same isolation criteria used in the experimental analysis are used to identify prompt photons for better comparison. For the first time, high-accuracy JETSCAPE results are compared with multi-energy LHC and RHIC measurements to better understand the deviations observed in prior studies. This study highlights the importance of multistage evolution for the simultaneous description of experimental observables through different collision systems and energies using a single parameter tune. △ Less

Submitted 30 January, 2024; originally announced January 2024.

Comments: 4 pages, 5 figures. Proceedings of Quark Matter 2023 - XXXth International Conference on Ultra-relativistic Nucleus-Nucleus Collisions, Houston, TX, 3-9 September 2023

Measuring jet quenching with a Bayesian inference analysis of hadron and jet data by JETSCAPE

Authors: R. Ehlers, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, L. Du, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, M. Kordell II, A. Kumar, R. Kunnawalkam-Elayavalli, J. Latessa, S. Lee, Y. -J. Lee, D. Liyanage , et al. (28 additional authors not shown)

Abstract: The JETSCAPE Collaboration reports the first multi-messenger study of the QGP jet transport parameter $\hat{q}$ using Bayesian inference, incorporating all available hadron and jet inclusive yield and jet substructure data from RHIC and the LHC. The theoretical model utilizes virtuality-dependent in-medium partonic energy loss coupled to a detailed dynamical model of QGP evolution. Tension is obse… ▽ More The JETSCAPE Collaboration reports the first multi-messenger study of the QGP jet transport parameter $\hat{q}$ using Bayesian inference, incorporating all available hadron and jet inclusive yield and jet substructure data from RHIC and the LHC. The theoretical model utilizes virtuality-dependent in-medium partonic energy loss coupled to a detailed dynamical model of QGP evolution. Tension is observed when constraining $\hat{q}$ for different kinematic cuts of the inclusive hadron data. The addition of substructure data is shown to improve the constraint on $\hat{q}$, without inducing tension with the constraint due to inclusive observables. These studies provide new insight into the mechanisms of jet interactions in matter, and point to next steps in the field for comprehensive understanding of jet quenching as a probe of the QGP. △ Less

Submitted 8 January, 2024; originally announced January 2024.

Comments: 4 pages, 2 figures. Proceedings of Quark Matter 2023 - XXXth International Conference on Ultra-relativistic Nucleus-Nucleus Collisions, Houston, TX, 3-9 September 2023

3D Multi-system Bayesian Calibration with Energy Conservation to Study Rapidity-dependent Dynamics of Nuclear Collisions

Authors: Andi Mankolli, Aaron Angerami, Ritu Arora, Steffen Bass, Shanshan Cao, Yi Chen, Lipei Du, Raymond Ehlers, Hannah Elfner, Wenkai Fan, Rainer J. Fries, Charles Gale, Yayun He, Ulrich Heinz, Barbara Jacak, Peter Jacobs, Sangyong Jeon, Yi Ji, Lauren Kasper, Michael Kordell II, Amit Kumar, R. Kunnawalkam-Elayavalli, Joseph Latessa, Sook H. Lee, Yen-Jie Lee , et al. (26 additional authors not shown)

Abstract: Considerable information about the early-stage dynamics of heavy-ion collisions is encoded in the rapidity dependence of measurements. To leverage the large amount of experimental data, we perform a systematic analysis using three-dimensional hydrodynamic simulations of multiple collision systems -- large and small, symmetric and asymmetric. Specifically, we perform fully 3D multi-stage hydrodynam… ▽ More Considerable information about the early-stage dynamics of heavy-ion collisions is encoded in the rapidity dependence of measurements. To leverage the large amount of experimental data, we perform a systematic analysis using three-dimensional hydrodynamic simulations of multiple collision systems -- large and small, symmetric and asymmetric. Specifically, we perform fully 3D multi-stage hydrodynamic simulations initialized by a parameterized model for rapidity-dependent energy deposition, which we calibrate on the hadron multiplicity and anisotropic flow coefficients. We utilize Bayesian inference to constrain properties of the early- and late- time dynamics of the system, and highlight the impact of enforcing global energy conservation in our 3D model. △ Less

Submitted 31 December, 2023; originally announced January 2024.

Hybrid Hadronization of Jet Showers from $e^++e^-$ to $A+A$ with JETSCAPE

Authors: Cameron Parker, Aaron Angerami, Ritu Arora, Steffen Bass, Shanshan Cao, Yi Chen, Raymond Ehlers, Hannah Elfner, Wenkai Fan, Rainer J. Fries, Charles Gale, Yayun He, Ulrich Heinz, Barbara Jacak, Peter Jacobs, Sangyong Jeon, Yi Ji, Lauren Kasper, Michael Kordell II, Amit Kumar, Joseph Latessa, Yen-Jie Lee, Roy Lemmon, Dananjaya Liyanage, Arthur Lopez , et al. (26 additional authors not shown)

Abstract: In this talk we review jet production in a large variety of collision systems using the JETSCAPE event generator and Hybrid Hadronization. Hybrid Hadronization combines quark recombination, applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems. It can therefore smoothly describe the transition from very dilute parton syst… ▽ More In this talk we review jet production in a large variety of collision systems using the JETSCAPE event generator and Hybrid Hadronization. Hybrid Hadronization combines quark recombination, applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems. It can therefore smoothly describe the transition from very dilute parton systems like $e^++e^-$ to full $A+A$ collisions. We test this picture by using JETSCAPE to generate jets in various systems. Comparison to experimental data in $e^++e^-$ and $p+p$ collisions allows for a precise tuning of vacuum baseline parameters in JETSCAPE and Hybrid Hadronization. Proceeding to systems with jets embedded in a medium, we study in-medium hadronization for jet showers. We quantify the effects of an ambient medium, focusing in particular on the dependence on the collective flow and size of the medium. Our results clarify the effects we expect from in-medium hadronization of jets on observables like fragmentation functions, hadron chemistry and jet shape. △ Less

Submitted 7 November, 2023; v1 submitted 31 October, 2023; originally announced October 2023.

Comments: 6 pages, 4 figures, Hard Probes 2023 conference, accepted for publication in Proceedings of Science: version 2, references added, typos fixed

A multistage framework for studying the evolution of jets and high-$p_T$ probes in small collision systems

Authors: Abhijit Majumder, Aaron Angerami, Ritu Arora, Steffen Bass, Shanshan Cao, Yi Chen, Raymond Ehlers, Hannah Elfner, Wenkai Fan, Rainer J. Fries, Charles Gale, Yayun He, Ulrich Heinz, Barbara Jacak, Peter Jacobs, Sangyong Jeon, Yi Ji, Lauren Kasper, Michael Kordell II, Amit Kumar, Joseph Latessa, Yen-Jie Lee, Roy Lemmon, Dananjaya Liyanage, Arthur Lopez , et al. (26 additional authors not shown)

Abstract: Understanding the modification of jets and high-$p_T$ probes in small systems requires the integration of soft and hard physics. We present recent developments in extending the JETSCAPE framework to build an event generator, which includes correlations between soft and hard partons, to study jet observables in small systems. The multi-scale physics of the collision is separated into different stag… ▽ More Understanding the modification of jets and high-$p_T$ probes in small systems requires the integration of soft and hard physics. We present recent developments in extending the JETSCAPE framework to build an event generator, which includes correlations between soft and hard partons, to study jet observables in small systems. The multi-scale physics of the collision is separated into different stages. Hard scatterings are first sampled at binary collision positions provided by the Glauber geometry. They are then propagated backward in space-time following an initial-state shower to obtain the initiating partons' energies and momenta before the collision. These energies and momenta are then subtracted from the incoming colliding nucleons for soft-particle production, modeled by the 3D-Glauber + hydrodynamics + hadronic transport framework. This new hybrid approach (X-SCAPE) includes non-trivial correlations between jet and soft particle productions in small systems. We calibrate this framework with the final state hadrons' $p_T$-spectra from low to high $p_T$ in $p$-$p$, and and then compare with the spectra in $p$-$Pb$ collisions from the LHC. We also present results for additional observables such as the distributions of event activity as a function of the hardest jet $p_T$ in forward and mid-rapidity for both $p$-$p$ and $p$-$Pb$ collisions. △ Less

Submitted 1 November, 2023; v1 submitted 4 August, 2023; originally announced August 2023.

Comments: 6 pages, 6 figures, Proceedings of Hard Probes 2023, 26-31 March 2023 Aschaffenburg, Germany

Journal ref: Proceedings of Science (Hard Probes 2023) 2023

A new metric improving Bayesian calibration of a multistage approach studying hadron and inclusive jet suppression

Authors: W. Fan, G. Vujanovic, S. A. Bass, A. Angerami, R. Arora, S. Cao, Y. Chen, T. Dai, L. Du, R. Ehlers, H. Elfner, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, M. Kordell II, A. Kumar, J. Latessa, Y. -J. Lee , et al. (30 additional authors not shown)

Abstract: We study parton energy-momentum exchange with the quark gluon plasma (QGP) within a multistage approach composed of in-medium DGLAP evolution at high virtuality, and (linearized) Boltzmann Transport formalism at lower virtuality. This multistage simulation is then calibrated in comparison with high $p_T$ charged hadrons, D-mesons, and the inclusive jet nuclear modification factors, using Bayesian… ▽ More We study parton energy-momentum exchange with the quark gluon plasma (QGP) within a multistage approach composed of in-medium DGLAP evolution at high virtuality, and (linearized) Boltzmann Transport formalism at lower virtuality. This multistage simulation is then calibrated in comparison with high $p_T$ charged hadrons, D-mesons, and the inclusive jet nuclear modification factors, using Bayesian model-to-data comparison, to extract the virtuality-dependent transverse momentum broadening transport coefficient $\hat{q}$. To facilitate this undertaking, we develop a quantitative metric for validating the Bayesian workflow, which is used to analyze the sensitivity of various model parameters to individual observables. The usefulness of this new metric in improving Bayesian model emulation is shown to be highly beneficial for future such analyses. △ Less

Submitted 27 October, 2023; v1 submitted 18 July, 2023; originally announced July 2023.

Comments: 24 pages, 16 figures

Multiscale evolution of heavy flavor in the QGP

Authors: G. Vujanovic, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, T. Dai, L. Du, R. Ehlers, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, M. Kordell II, A. Kumar, J. Latessa, Y. -J. Lee , et al. (30 additional authors not shown)

Abstract: Shower development dynamics for a jet traveling through the quark-gluon plasma (QGP) is a multiscale process, where the heavy flavor mass is an important scale. During the high virtuality portion of the jet evolution in the QGP, emission of gluons from a heavy flavor is modified owing to heavy quark mass. Medium-induced radiation of heavy flavor is sensitive to microscopic processes (e.g. diffusio… ▽ More Shower development dynamics for a jet traveling through the quark-gluon plasma (QGP) is a multiscale process, where the heavy flavor mass is an important scale. During the high virtuality portion of the jet evolution in the QGP, emission of gluons from a heavy flavor is modified owing to heavy quark mass. Medium-induced radiation of heavy flavor is sensitive to microscopic processes (e.g. diffusion), whose virtuality dependence is phenomenologically explored in this study. In the lower virtuality part of shower evolution, i.e. when the mass is comparable to the virtuality of the parton, scattering and radiation processes of heavy quarks differ from light quarks. The effects of these mechanisms on shower development in heavy flavor tagged showers in the QGP is explored here. Furthermore, this multiscale study examines dynamical pair production of heavy flavor (via virtual gluon splittings) and their subsequent evolution in the QGP, which is not possible otherwise. A realistic event-by-event simulation is performed using the JETSCAPE framework. Energy-momentum exchange with the medium proceeds using a weak coupling recoil approach. Using leading hadron and open heavy flavor observables, differences in heavy versus light quark energy-loss mechanisms are explored, while the importance of heavy flavor pair production is highlighted along with future directions to study. △ Less

Submitted 27 October, 2023; v1 submitted 18 July, 2023; originally announced July 2023.

Comments: 6 pages, 3 figures, contribution to the Hard Probes 2023 proceedings

Effects of multi-scale jet-medium interactions on jet substructures

Authors: JETSCAPE Collaboration, Y. Tachibana, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, T. Dai, L. Du, R. Ehlers, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, K. Kauder, L. Kasper, W. Ke, M. Kelsey , et al. (35 additional authors not shown)

Abstract: We utilize event-by-event Monte Carlo simulations within the JETSCAPE framework to examine scale-dependent jet-medium interactions in heavy-ion collisions. The reduction in jet-medium interaction during the early high-virtuality stage, where the medium is resolved at a short distance scale, is emphasized as a key element in explaining multiple jet observables, particularly substructures, simultane… ▽ More We utilize event-by-event Monte Carlo simulations within the JETSCAPE framework to examine scale-dependent jet-medium interactions in heavy-ion collisions. The reduction in jet-medium interaction during the early high-virtuality stage, where the medium is resolved at a short distance scale, is emphasized as a key element in explaining multiple jet observables, particularly substructures, simultaneously. By employing the MATTER+LBT setup, which incorporates this explicit reduction of medium effects at high virtuality, we investigate jet substructure observables, such as Soft Drop groomed observables. When contrasted with existing data, our findings spotlight the significant influence of the reduction at the early high-virtuality stages. Furthermore, we study the substructure of gamma-tagged jets, providing predictive insights for future experimental analyses. This broadens our understanding of the various contributing factors involved in modifying jet substructures. △ Less

Submitted 16 July, 2023; originally announced July 2023.

Comments: 6 pages, 4 figures, contribution to the Hard Probes 2023 proceedings

The case for an EIC Theory Alliance: Theoretical Challenges of the EIC

Authors: Raktim Abir, Igor Akushevich, Tolga Altinoluk, Daniele Paolo Anderle, Fatma P. Aslan, Alessandro Bacchetta, Baha Balantekin, Joao Barata, Marco Battaglieri, Carlos A. Bertulani, Guillaume Beuf, Chiara Bissolotti, Daniël Boer, M. Boglione, Radja Boughezal, Eric Braaten, Nora Brambilla, Vladimir Braun, Duane Byer, Francesco Giovanni Celiberto, Yang-Ting Chien, Ian C. Cloët, Martha Constantinou, Wim Cosyn, Aurore Courtoy , et al. (146 additional authors not shown)

Abstract: We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize thi… ▽ More We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize this ambitious and impactful physics program, including how to engage a diverse and inclusive workforce. In order to address these many-fold challenges, we propose a coordinated effort involving theory groups with differing expertise is needed. We discuss the scientific goals and scope of such an EIC Theory Alliance. △ Less

Submitted 23 May, 2023; originally announced May 2023.

Comments: 44 pages, ReVTeX, White Paper on EIC Theory Alliance

Hot QCD White Paper

Authors: M. Arslandok, S. A. Bass, A. A. Baty, I. Bautista, C. Beattie, F. Becattini, R. Bellwied, Y. Berdnikov, A. Berdnikov, J. Bielcik, J. T. Blair, F. Bock, B. Boimska, H. Bossi, H. Caines, Y. Chen, Y. -T. Chien, M. Chiu, M. E. Connors, M. Csanád, C. L. da Silva, A. P. Dash, G. David, K. Dehmelt, V. Dexheimer , et al. (149 additional authors not shown)

Abstract: Hot QCD physics studies the nuclear strong force under extreme temperature and densities. Experimentally these conditions are achieved via high-energy collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). In the past decade, a unique and substantial suite of data was collected at RHIC and the LHC, probing hydrodynamics at the nucleon scale, the… ▽ More Hot QCD physics studies the nuclear strong force under extreme temperature and densities. Experimentally these conditions are achieved via high-energy collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). In the past decade, a unique and substantial suite of data was collected at RHIC and the LHC, probing hydrodynamics at the nucleon scale, the temperature dependence of the transport properties of quark-gluon plasma, the phase diagram of nuclear matter, the interaction of quarks and gluons at different scales and much more. This document, as part of the 2023 nuclear science long range planning process, was written to review the progress in hot QCD since the 2015 Long Range Plan for Nuclear Science, as well as highlight the realization of previous recommendations, and present opportunities for the next decade, building on the accomplishments and investments made in theoretical developments and the construction of new detectors. Furthermore, this document provides additional context to support the recommendations voted on at the Joint Hot and Cold QCD Town Hall Meeting, which are reported in a separate document. △ Less

Submitted 30 March, 2023; originally announced March 2023.

Comments: 190 pages, 69 figures

Hard jet substructure in a multistage approach

Authors: Y. Tachibana, A. Kumar, A. Majumder, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, T. Dai, L. Du, R. Ehlers, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, K. Kauder, L. Kasper, W. Ke , et al. (34 additional authors not shown)

Abstract: We present predictions and postdictions for a wide variety of hard jet-substructure observables using a multistage model within the JETSCAPE framework. The details of the multistage model and the various parameter choices are described in [A. Kumar et al., arXiv:2204.01163]. A novel feature of this model is the presence of two stages of jet modification: a high virtuality phase [modeled using the… ▽ More We present predictions and postdictions for a wide variety of hard jet-substructure observables using a multistage model within the JETSCAPE framework. The details of the multistage model and the various parameter choices are described in [A. Kumar et al., arXiv:2204.01163]. A novel feature of this model is the presence of two stages of jet modification: a high virtuality phase [modeled using the modular all twist transverse-scattering elastic-drag and radiation model (MATTER)], where modified coherence effects diminish medium-induced radiation, and a lower virtuality phase [modeled using the linear Boltzmann transport model (LBT)], where parton splits are fully resolved by the medium as they endure multiple scattering induced energy loss. Energy-loss calculations are carried out on event-by-event viscous fluid dynamic backgrounds constrained by experimental data. The uniform and consistent descriptions of multiple experimental observables demonstrate the essential role of modified coherence effects and the multistage modeling of jet evolution. Using the best choice of parameters from [A. Kumar et al., arXiv:2204.01163], and with no further tuning, we present calculations for the medium modified jet fragmentation function, the groomed jet momentum fraction $z_g$ and angular separation $r_g$ distributions, as well as the nuclear modification factor of groomed jets. These calculations provide accurate descriptions of published data from experiments at the Large Hadron Collider. Furthermore, we provide predictions from the multistage model for future measurements at the BNL Relativistic Heavy Ion Collider. △ Less

Submitted 16 October, 2024; v1 submitted 6 January, 2023; originally announced January 2023.

Comments: 20 pages, 12 figures

Journal ref: Phys. Rev. C 110, 044907 (2024)

Comprehensive Study of Multi-scale Jet-medium Interaction

Authors: Y. Tachibana, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, T. Dai, L. Du, R. Ehlers, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, W. Ke, M. Kelsey, M. Kordell II, A. Kumar , et al. (33 additional authors not shown)

Abstract: We explore jet-medium interactions at various scales in high-energy heavy-ion collisions using the JETSCAPE framework. The physics of the multi-stage modeling and the coherence effect at high virtuality is discussed through the results of multiple jet and high-$p_{\mathrm{T}}$ particle observables, compared with experimental data. Furthermore, we investigate the jet-medium interaction involved in… ▽ More We explore jet-medium interactions at various scales in high-energy heavy-ion collisions using the JETSCAPE framework. The physics of the multi-stage modeling and the coherence effect at high virtuality is discussed through the results of multiple jet and high-$p_{\mathrm{T}}$ particle observables, compared with experimental data. Furthermore, we investigate the jet-medium interaction involved in the hadronization process. △ Less

Submitted 23 December, 2022; originally announced December 2022.

Comments: 6 pages, 5 figures, contribution to the Quark Matter 2022 proceedings

Journal ref: Acta Phys. Pol. B Proc. Suppl. 16, 1-A50 (2023)

Quenching jets increases their flavor

Authors: Chathuranga Sirimanna, Ismail Soudi, Gojko Vujanovic, Wen-Jing Xing, Shanshan Cao, Abhijit Majumder

Abstract: The widespread notion that jets quenched in a Quark-Gluon-Plasma (QGP) are similar in their parton flavor composition to jets in vacuum is critically examined. We demonstrate that while the soft to semi-hard [low to intermediate transverse momentum ($p_T$)] sector of vacuum jets are predominantly bosonic i.e., composed of gluons, \emph{sufficiently} quenched jets can have an intermediate momentum… ▽ More The widespread notion that jets quenched in a Quark-Gluon-Plasma (QGP) are similar in their parton flavor composition to jets in vacuum is critically examined. We demonstrate that while the soft to semi-hard [low to intermediate transverse momentum ($p_T$)] sector of vacuum jets are predominantly bosonic i.e., composed of gluons, \emph{sufficiently} quenched jets can have an intermediate momentum sector that is predominantly fermionic, dominated by quarks and antiquarks. We demonstrate, using leading order perturbative QCD processes, that the rate of flavor conversion from a gluon traversing the QGP as part of a jet, to a quark or antiquark, versus the reverse process, grows steadily with falling $p_T$. Simple diagrammatic estimates are followed by a variety of realistic simulations in static media. The relation of this increase in flavor to the observed baryon enhancement at intermediate $p_T$ is studied in a fully realistic simulation. △ Less

Submitted 16 May, 2023; v1 submitted 28 November, 2022; originally announced November 2022.

Comments: 17 pages, 14 figures

Electromagnetic probes of the Quark-Gluon Plasma

Authors: Gojko Vujanovic

Abstract: The penetrating nature of electromagnetic probes makes them an ideal candidate to study properties of the Quark-Gluon Plasma (QGP). A selection of recent developments in the theory and phenomenology of electromagnetic probes is discussed, with an emphasis given towards how these probes can be used to constrain QGP trapnsport coefficients. A Bayesian treatment of electromagnetic radiation, similar… ▽ More The penetrating nature of electromagnetic probes makes them an ideal candidate to study properties of the Quark-Gluon Plasma (QGP). A selection of recent developments in the theory and phenomenology of electromagnetic probes is discussed, with an emphasis given towards how these probes can be used to constrain QGP trapnsport coefficients. A Bayesian treatment of electromagnetic radiation, similar to the one of soft hadronic observables and jets, is suggested as a path towards imposing more stringent constraints on various transport coefficients of the QCD medium. △ Less

Submitted 19 August, 2022; originally announced August 2022.

Comments: 8 pages, 2 figures, Presented at the XXIXth International Conference on Ultra-relativistic Nucleus-Nucleus Collisions (Quark Matter 2022)

Bayesian analysis of QGP jet transport using multi-scale modeling applied to inclusive hadron and reconstructed jet data

Authors: R. Ehlers, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, L. Du, T. Dai, H. Elfner, W. Fan, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, L. Kasper, W. Ke, M. Kelsey, M. Kordell II, A. Kumar, J. Latessa , et al. (33 additional authors not shown)

Abstract: The JETSCAPE Collaboration reports a new determination of jet transport coefficients in the Quark-Gluon Plasma, using both reconstructed jet and hadron data measured at RHIC and the LHC. The JETSCAPE framework incorporates detailed modeling of the dynamical evolution of the QGP; a multi-stage theoretical approach to in-medium jet evolution and medium response; and Bayesian inference for quantitati… ▽ More The JETSCAPE Collaboration reports a new determination of jet transport coefficients in the Quark-Gluon Plasma, using both reconstructed jet and hadron data measured at RHIC and the LHC. The JETSCAPE framework incorporates detailed modeling of the dynamical evolution of the QGP; a multi-stage theoretical approach to in-medium jet evolution and medium response; and Bayesian inference for quantitative comparison of model calculations and data. The multi-stage framework incorporates multiple models to cover a broad range in scale of the in-medium parton shower evolution, with dynamical choice of model that depends on the current virtuality or energy of the parton. We will discuss the physics of the multi-stage modeling, and then present a new Bayesian analysis incorporating it. This analysis extends the recently published JETSCAPE determination of the jet transport parameter $\hat{q}$ that was based solely on inclusive hadron suppression data, by incorporating reconstructed jet measurements of quenching. We explore the functional dependence of jet transport coefficients on QGP temperature and jet energy and virtuality, and report the consistency and tensions found for current jet quenching modeling with hadron and reconstructed jet data over a wide range in kinematics and $\sqrt{s_{\text{NN}}}$. This analysis represents the next step in the program of comprehensive analysis of jet quenching phenomenology and its constraint of properties of the QGP. △ Less

Submitted 16 August, 2022; originally announced August 2022.

Comments: 6 pages, 2 figures, contribution to the Quark Matter 2022 proceedings

Multi-scale evolution of charmed particles in a nuclear medium

Authors: JETSCAPE collaboration, W. Fan, G. Vujanovic, S. A. Bass, A. Majumder, A. Angerami, R. Arora, S. Cao, Y. Chen, T. Dai, L. Du, R. Ehlers, H. Elfner, R. J. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, Y. Ji, K. Kauder, L. Kasper, W. Ke , et al. (35 additional authors not shown)

Abstract: Parton energy-momentum exchange with the quark gluon plasma (QGP) is a multi-scale problem. In this work, we calculate the interaction of charm quarks with the QGP within the higher twist formalism at high virtuality and high energy using the MATTER model, while the low virtuality and high energy portion is treated via a (linearized) Boltzmann Transport (LBT) formalism. Coherence effect that reduc… ▽ More Parton energy-momentum exchange with the quark gluon plasma (QGP) is a multi-scale problem. In this work, we calculate the interaction of charm quarks with the QGP within the higher twist formalism at high virtuality and high energy using the MATTER model, while the low virtuality and high energy portion is treated via a (linearized) Boltzmann Transport (LBT) formalism. Coherence effect that reduces the medium-induced emission rate in the MATTER model is also taken into account. The interplay between these two formalisms is studied in detail and used to produce a good description of the D-meson and charged hadron nuclear modification factor RAA across multiple centralities. All calculations were carried out utilizing the JETSCAPE framework. △ Less

Submitted 13 May, 2023; v1 submitted 1 August, 2022; originally announced August 2022.

Journal ref: 107(5), 2023, 054901

Inclusive jet and hadron suppression in a multistage approach

Authors: A. Kumar, Y. Tachibana, C. Sirimanna, G. Vujanovic, S. Cao, A. Majumder, Y. Chen, L. Du, R. Ehlers, D. Everett, W. Fan, Y. He, J. Mulligan, C. Park, A. Angerami, R. Arora, S. A. Bass, T. Dai, H. Elfner, R. J. Fries, C. Gale, F. Garza, M. Heffernan, U. Heinz, B. V. Jacak , et al. (35 additional authors not shown)

Abstract: We present a new study of jet interactions in the quark-gluon plasma created in high-energy heavy-ion collisions, using a multistage event generator within the JETSCAPE framework. We focus on medium-induced modifications in the rate of inclusive jets and high transverse momentum (high-$p_{\mathrm{T}}$) hadrons. Scattering-induced jet energy loss is calculated in two stages: A high virtuality stage… ▽ More We present a new study of jet interactions in the quark-gluon plasma created in high-energy heavy-ion collisions, using a multistage event generator within the JETSCAPE framework. We focus on medium-induced modifications in the rate of inclusive jets and high transverse momentum (high-$p_{\mathrm{T}}$) hadrons. Scattering-induced jet energy loss is calculated in two stages: A high virtuality stage based on the MATTER model, in which scattering of highly virtual partons modifies the vacuum radiation pattern, and a second stage at lower jet virtuality based on the LBT model, in which leading partons gain and lose virtuality by scattering and radiation. Coherence effects that reduce the medium-induced emission rate in the MATTER phase are also included. The TRENTo model is used for initial conditions, and the (2+1)dimensional VISHNU model is used for viscous hydrodynamic evolution. Jet interactions with the medium are modeled via 2-to-2 scattering with Debye screened potentials, in which the recoiling partons are tracked, hadronized, and included in the jet clustering. Holes left in the medium are also tracked and subtracted to conserve transverse momentum. Calculations of the nuclear modification factor ($R_{\mathrm{AA}}$) for inclusive jets and high-$p_{\mathrm{T}}$ hadrons are compared to experimental measurements at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Within this framework, we find that with one extra parameter which codifies the transition between stages of jet modification -- along with the typical parameters such as the coupling in the medium, the start and stop criteria etc. -- we can describe these data at all energies for central and semicentral collisions without a rescaling of the jet transport coefficient $\hat{q}$. △ Less

Submitted 16 April, 2023; v1 submitted 3 April, 2022; originally announced April 2022.

Comments: 34 pages, 23 figures

Journal ref: Phys. Rev. C 107, no.3, 034911 (2023)

Role of bulk viscosity in deuteron production in ultrarelativistic nuclear collisions

Authors: D. Everett, D. Oliinychenko, M. Luzum, J. -F. Paquet, G. Vujanovic, S. A. Bass, L. Du, C. Gale, M. Heffernan, U. Heinz, L. Kasper, W. Ke, D. Liyanage, A. Majumder, A. Mankolli, C. Shen, D. Soeder, J. Velkovska, A. Angerami, R. Arora, S. Cao, Y. Chen, T. Dai, R. Ehlers, H. Elfner , et al. (31 additional authors not shown)

Abstract: We use a Bayesian-calibrated multistage viscous hydrodynamic model to explore deuteron yield, mean transverse momentum and flow observables in LHC Pb-Pb collisions. We explore theoretical uncertainty in the production of deuterons, including (i) the contribution of thermal deuterons, (ii) models for the subsequent formation of deuterons (hadronic transport vs coalescence) and (iii) the overall sen… ▽ More We use a Bayesian-calibrated multistage viscous hydrodynamic model to explore deuteron yield, mean transverse momentum and flow observables in LHC Pb-Pb collisions. We explore theoretical uncertainty in the production of deuterons, including (i) the contribution of thermal deuterons, (ii) models for the subsequent formation of deuterons (hadronic transport vs coalescence) and (iii) the overall sensitivity of the results to the hydrodynamic model -- in particular to bulk viscosity, which is often neglected in studies of deuteron production. Using physical parameters set by a comparison to only light hadron observables, we find good agreement with measurements of the mean transverse momentum $\langle p_T \rangle$ and elliptic flow $v_2$ of deuterons; however, tension is observed with experimental data for the deuteron multiplicity in central collisions. The results are found to be sensitive to each of the mentioned theoretical uncertainties, with a particular sensitivity to bulk viscosity, indicating that the latter is an important ingredient for an accurate treatment of deuteron production. △ Less

Submitted 15 March, 2022; originally announced March 2022.

Comments: 11 pages, 8 figures

Determining the jet transport coefficient $\hat{q}$ of the quark-gluon plasma using Bayesian parameter estimation

Authors: J. Mulligan, A. Angerami, R. Arora, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, F. Garza, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, W. Ke, B. Kim , et al. (24 additional authors not shown)

Abstract: We present a new determination of $\hat{q}$, the jet transport coefficient of the quark-gluon plasma. Using the JETSCAPE framework, we use Bayesian parameter estimation to constrain the dependence of $\hat{q}$ on the jet energy, virtuality, and medium temperature from experimental measurements of inclusive hadron suppression in Au-Au collisions at RHIC and Pb-Pb collisions at the LHC. These result… ▽ More We present a new determination of $\hat{q}$, the jet transport coefficient of the quark-gluon plasma. Using the JETSCAPE framework, we use Bayesian parameter estimation to constrain the dependence of $\hat{q}$ on the jet energy, virtuality, and medium temperature from experimental measurements of inclusive hadron suppression in Au-Au collisions at RHIC and Pb-Pb collisions at the LHC. These results are based on a multi-stage theoretical approach to in-medium jet evolution with the MATTER and LBT jet quenching models. The functional dependence of $\hat{q}$ on jet energy, virtuality, and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. These results provide state-of-the-art constraints on $\hat{q}$ and lay the groundwork to extract additional properties of the quark-gluon plasma from jet measurements in heavy-ion collisions. △ Less

Submitted 21 June, 2021; originally announced June 2021.

Comments: contribution to the 2021 QCD session of the 55th Recontres de Moriond

Determining the jet transport coefficient $\hat{q}$ from inclusive hadron suppression measurements using Bayesian parameter estimation

Authors: S. Cao, Y. Chen, J. Coleman, J. Mulligan, P. M. Jacobs, R. A. Soltz, A. Angerami, R. Arora, S. A. Bass, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. J. Fries, C. Gale, F. Garza, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, S. Jeon, W. Ke , et al. (22 additional authors not shown)

Abstract: We report a new determination of $\hat{q}$, the jet transport coefficient of the Quark-Gluon Plasma. We use the JETSCAPE framework, which incorporates a novel multi-stage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the MATTER and LBT jet quenching models, are compared to experimental measurements of inclusive hadron su… ▽ More We report a new determination of $\hat{q}$, the jet transport coefficient of the Quark-Gluon Plasma. We use the JETSCAPE framework, which incorporates a novel multi-stage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the MATTER and LBT jet quenching models, are compared to experimental measurements of inclusive hadron suppression in Au+Au collisions at RHIC and Pb+Pb collisions at the LHC. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. The functional dependence of $\hat{q}$ on jet energy or virtuality and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. In the multi-stage approach, the switch between MATTER and LBT is governed by a virtuality scale $Q_0$. Comparison of the posterior model predictions to the RHIC and LHC hadron suppression data shows reasonable agreement, with moderate tension in limited regions of phase space. The distribution of $\hat{q}/T^3$ extracted from the posterior distributions exhibits weak dependence on jet momentum and medium temperature $T$, with 90\% Credible Region (CR) depending on the specific choice of model configuration. The choice of MATTER+LBT, with switching at virtuality $Q_0$, has 90\% CR of $2<\hat{q}/T^3<4$ for $p_\mathrm{T}^\mathrm{jet}>40$ GeV/c. The value of $Q_0$, determined here for the first time, is in the range 2.0-2.7 GeV. △ Less

Submitted 28 July, 2021; v1 submitted 22 February, 2021; originally announced February 2021.

Comments: Published in Phys Rev C

Journal ref: Phys. Rev. C 104, 024905 (2021)

Multi-system Bayesian constraints on the transport coefficients of QCD matter

Authors: D. Everett, W. Ke, J. -F. Paquet, G. Vujanovic, S. A. Bass, L. Du, C. Gale, M. Heffernan, U. Heinz, D. Liyanage, M. Luzum, A. Majumder, M. McNelis, C. Shen, Y. Xu, A. Angerami, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, R. Ehlers, H. Elfner, W. Fan, R. J. Fries , et al. (23 additional authors not shown)

Abstract: We study the properties of the strongly-coupled quark-gluon plasma with a multistage model of heavy ion collisions that combines the T$_\mathrm{R}$ENTo initial condition ansatz, free-streaming, viscous relativistic hydrodynamics, and a relativistic hadronic transport. A model-to-data comparison with Bayesian inference is performed, revisiting assumptions made in previous studies. The role of param… ▽ More We study the properties of the strongly-coupled quark-gluon plasma with a multistage model of heavy ion collisions that combines the T$_\mathrm{R}$ENTo initial condition ansatz, free-streaming, viscous relativistic hydrodynamics, and a relativistic hadronic transport. A model-to-data comparison with Bayesian inference is performed, revisiting assumptions made in previous studies. The role of parameter priors is studied in light of their importance towards the interpretation of results. We emphasize the use of closure tests to perform extensive validation of the analysis workflow before comparison with observations. Our study combines measurements from the Large Hadron Collider and the Relativistic Heavy Ion Collider, achieving a good simultaneous description of a wide range of hadronic observables from both colliders. The selected experimental data provide reasonable constraints on the shear and the bulk viscosities of the quark-gluon plasma at $T\sim$ 150-250 MeV, but their constraining power degrades at higher temperatures $T \gtrsim 250$ MeV. Furthermore, these viscosity constraints are found to depend significantly on how viscous corrections are handled in the transition from hydrodynamics to the hadronic transport. Several other model parameters, including the free-streaming time, show similar model sensitivity while the initial condition parameters associated with the T$_\mathrm{R}$ENTo ansatz are quite robust against variations of the particlization prescription. We also report on the sensitivity of individual observables to the various model parameters. Finally, Bayesian model selection is used to quantitatively compare the agreement with measurements for different sets of model assumptions, including different particlization models and different choices for which parameters are allowed to vary between RHIC and LHC energies. △ Less

Submitted 6 November, 2020; v1 submitted 2 November, 2020; originally announced November 2020.

Comments: 51 pages, including 35 figures and 8 appendices, long companion paper to arXiv:2010.03928. A useful visualization tool to see the effect of varying individual model parameters on physical observables can be found at jetscape.org/sims-widget. Some references and discussion added. This version submitted for publication

Journal ref: Phys. Rev. C 103, 054904 (2021)

Phenomenological constraints on the transport properties of QCD matter with data-driven model averaging

Authors: D. Everett, W. Ke, J. -F. Paquet, G. Vujanovic, S. A. Bass, L. Du, C. Gale, M. Heffernan, U. Heinz, D. Liyanage, M. Luzum, A. Majumder, M. McNelis, C. Shen, Y. Xu, A. Angerami, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, R. Ehlers, H. Elfner, W. Fan, R. J. Fries , et al. (23 additional authors not shown)

Abstract: Using combined data from the Relativistic Heavy Ion and Large Hadron Colliders, we constrain the shear and bulk viscosities of quark-gluon plasma (QGP) at temperatures of ${\sim\,}150{-}350$ MeV. We use Bayesian inference to translate experimental and theoretical uncertainties into probabilistic constraints for the viscosities. With Bayesian Model Averaging we account for the irreducible model amb… ▽ More Using combined data from the Relativistic Heavy Ion and Large Hadron Colliders, we constrain the shear and bulk viscosities of quark-gluon plasma (QGP) at temperatures of ${\sim\,}150{-}350$ MeV. We use Bayesian inference to translate experimental and theoretical uncertainties into probabilistic constraints for the viscosities. With Bayesian Model Averaging we account for the irreducible model ambiguities in the transition from a fluid description of the QGP to hadronic transport in the final evolution stage, providing the most reliable phenomenological constraints to date on the QGP viscosities. △ Less

Submitted 8 October, 2020; originally announced October 2020.

Comments: 8 pages, 3 figures

Journal ref: Phys. Rev. Lett. 126, 242301 (2021)

Probing the multi-scale dynamical interaction between heavy quarks and the QGP using JETSCAPE

Authors: W. Fan, G. Vujanovic, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, R. Fries, C. Gale, F. Garza, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, W. Ke, E. Khalaj, B. Kim , et al. (25 additional authors not shown)

Abstract: The dynamics of shower development for a jet traveling through the QGP involves a variety of scales, one of them being the heavy quark mass. Even though the mass of the heavy quarks plays a subdominant role during the high virtuality portion of the jet evolution, it does affect longitudinal drag and diffusion, stimulating additional radiation from heavy quarks. These emissions partially compensate… ▽ More The dynamics of shower development for a jet traveling through the QGP involves a variety of scales, one of them being the heavy quark mass. Even though the mass of the heavy quarks plays a subdominant role during the high virtuality portion of the jet evolution, it does affect longitudinal drag and diffusion, stimulating additional radiation from heavy quarks. These emissions partially compensate the reduction in radiation from the dead cone effect. In the lower virtuality part of the shower, when the mass is comparable to the transverse momenta of the partons, scattering and radiation processes off heavy quarks differ from those off light quarks. All these factors result in a different nuclear modification factor for heavy versus light flavors and thus for heavy-flavor tagged jets. In this study, the heavy quark shower evolution and the fluid dynamical medium are modeled on an event by event basis using the JETSCAPE Framework. We present a multi-stage calculation that explores the differences between various heavy quark energy-loss mechanisms within a realistically expanding quark-gluon plasma (QGP). Inside the QGP, the highly virtual and energetic portion of the shower is modeled using the MATTER generator, while the LBT generator models the showers induced by energetic and close-to-on-shell heavy quarks. Energy-momentum exchange with the medium, essential for the study of jet modification, proceeds using a weak coupling recoil approach. The JETSCAPE framework allows for transitions, on the level of individual partons, from one energy-loss prescription to the other depending on the parton's energy and virtuality and the local density. This allows us to explore the effect and interplay between the different regimes of energy loss on the propagation and radiation from hard heavy quarks in a dense medium. △ Less

Submitted 9 August, 2022; v1 submitted 10 September, 2020; originally announced September 2020.

Comments: arXiv admin note: substantial text overlap with arXiv:2002.06643

Photon-jet correlations in p-p and Pb-Pb collisions using JETSCAPE framework

Authors: C. Sirimanna, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, F. Garza, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, W. Ke, E. Khalaj, B. Kim , et al. (25 additional authors not shown)

Abstract: It is now well established that jet modification is a multistage effect; hence a single model alone cannot describe all facets of jet modification. The JETSCAPE framework is a multistage framework that uses several modules to simulate different stages of jet propagation through the QGP medium. These simulations require a set of parameters to ensure a smooth transition between stages. We fine tune… ▽ More It is now well established that jet modification is a multistage effect; hence a single model alone cannot describe all facets of jet modification. The JETSCAPE framework is a multistage framework that uses several modules to simulate different stages of jet propagation through the QGP medium. These simulations require a set of parameters to ensure a smooth transition between stages. We fine tune these parameters to successfully describe a variety of observables, such as the nuclear modification factors of leading hadrons and jets, jet shape, and jet fragmentation function. Photons can be produced in the hard scattering or as radiation from quarks inside jets. In this work, we study photon-jet transverse momentum imbalance and azimuthal correlation for both $p-p$ and $Pb-Pb$ collision systems. All the photons produced in each event, including the photons from hard scattering, radiation from the parton shower, and radiation from hadronization are considered with an isolation cut to directly compare with experimental data. The simulations are conducted using the same set of tuned parameters as used for the jet analysis. No new parameters are introduced or tuned. We demonstrate a significantly improved agreement with photons from $Pb-Pb$ collisions compared to prior efforts. This work provides an independent, parameter free verification of the multistage evolution framework. △ Less

Submitted 9 September, 2020; originally announced September 2020.

Comments: 4 pages, 7 figures

First results from Hybrid Hadronization in small and large systems

Authors: M. Kordell II, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, F. Garza, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, W. Ke, E. Khalaj, B. Kim , et al. (25 additional authors not shown)

Abstract: "Hybrid Hadronization" is a new Monte Carlo package to hadronize systems of partons. It smoothly combines quark recombination applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems, following the picture outlined by Han et al. [PRC 93, 045207 (2016)]. Hybrid Hadronization integrates with PYTHIA 8 and can be applied to a va… ▽ More "Hybrid Hadronization" is a new Monte Carlo package to hadronize systems of partons. It smoothly combines quark recombination applicable when distances between partons in phase space are small, and string fragmentation appropriate for dilute parton systems, following the picture outlined by Han et al. [PRC 93, 045207 (2016)]. Hybrid Hadronization integrates with PYTHIA 8 and can be applied to a variety of systems from $e^++e^-$ to $A+A$ collisions. It takes systems of partons and their color flow information, for example from a Monte Carlo parton shower generator, as input. In addition, if for $A+A$ collisions a thermal background medium is provided, the package allows sampling thermal partons that contribute to hadronization. Hybrid Hadronization is available for use as a standalone code and is also part of JETSCAPE since the 2.0 release. In these proceedings we review the physics concepts underlying Hybrid Hadronization and demonstrate how users can use the code with various parton shower Monte Carlos. We present calculations of hadron chemistry and fragmentation functions in small and large systems when Hybrid Hadronization is combined with parton shower Monte Carlos MATTER and LBT. In particular, we discuss observable effects of the recombination of shower partons with thermal partons. △ Less

Submitted 11 September, 2020; v1 submitted 8 September, 2020; originally announced September 2020.

Comments: 4 pages, 3 figures, Proceedings of Hard Probes 2020, 1-6 June 2020, Austin, Texas; Updated Author list

Constraints on jet quenching from a multi-stage energy-loss approach

Authors: C. Park, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, F. Garza, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, W. Ke, E. Khalaj, B. Kim , et al. (25 additional authors not shown)

Abstract: We present a multi-stage model for jet evolution through a quark-gluon plasma within the JETSCAPE framework. The multi-stage approach in JETSCAPE provides a unified description of distinct phases in jet shower contingent on the virtuality. We demonstrate a simultaneous description of leading hadron and integrated jet observables as well as jet $v_n$ using tuned parameters. Medium response to the j… ▽ More We present a multi-stage model for jet evolution through a quark-gluon plasma within the JETSCAPE framework. The multi-stage approach in JETSCAPE provides a unified description of distinct phases in jet shower contingent on the virtuality. We demonstrate a simultaneous description of leading hadron and integrated jet observables as well as jet $v_n$ using tuned parameters. Medium response to the jet quenching is implemented based on a weakly-coupled recoil prescription. We also explore the cone-size dependence of jet energy loss inside the plasma. △ Less

Submitted 11 September, 2020; v1 submitted 4 September, 2020; originally announced September 2020.

Comments: 4 pages, 4 figures, Proceedings of Hard Probes 2020, 1-6 June 2020, Austin, Texas

Learning about the QCD medium using electromagnetic and weak probes

Authors: Gojko Vujanovic

Abstract: Recent theoretical developments concerning radiation of electromagnetic and weak probes in ultra-relativistic heavy-ion collisions is overviewed. These proceedings focus on electromagnetic probes and briefly cover weak probes. An outlook regarding the future use of electromagnetic probes is formulated whereby a quantitative Bayesian comparison, simultaneously employing electromagnetic and hadronic… ▽ More Recent theoretical developments concerning radiation of electromagnetic and weak probes in ultra-relativistic heavy-ion collisions is overviewed. These proceedings focus on electromagnetic probes and briefly cover weak probes. An outlook regarding the future use of electromagnetic probes is formulated whereby a quantitative Bayesian comparison, simultaneously employing electromagnetic and hadronic calculations of experimental observables against data, is highlighted as a path towards a better understanding of the properties of the QCD medium. △ Less

Submitted 21 June, 2021; v1 submitted 26 August, 2020; originally announced August 2020.

Comments: 8 pages, 2 figures, Proceedings for the plenary talk given at the 10th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2020), June 1-5, 2020

Hydrodynamic response to jets with a source based on causal diffusion

Authors: Y. Tachibana, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, K. Kauder, W. Ke, E. Khalaj, M. Kordell II , et al. (25 additional authors not shown)

Abstract: We study the medium response to jet evolution in the quark-gluon plasma within the JETSCAPE framework. Recoil partons' medium response in the weakly coupled description is implemented in the multi-stage jet energy-loss model in the framework. As a further extension, the hydrodynamic description is rearranged to include in-medium jet transport based on a strong-coupling picture. To interface hydrod… ▽ More We study the medium response to jet evolution in the quark-gluon plasma within the JETSCAPE framework. Recoil partons' medium response in the weakly coupled description is implemented in the multi-stage jet energy-loss model in the framework. As a further extension, the hydrodynamic description is rearranged to include in-medium jet transport based on a strong-coupling picture. To interface hydrodynamics with jet energy-loss models, the hydrodynamic source term is modeled by a causal formulation employing the relativistic diffusion equation. The jet shape and fragmentation function are studied via realistic simulations with weakly coupled recoils. We also demonstrate modifications in the medium caused by the hydrodynamic response. △ Less

Submitted 27 February, 2020; originally announced February 2020.

Comments: 4 pages, 2 figures, contribution to the Quark Matter 2019 proceedings

Jet quenching in a multi-stage Monte Carlo approach

Authors: A. Kumar, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, K. Kauder, W. Ke, E. Khalaj, M. Kordell II , et al. (25 additional authors not shown)

Abstract: We present a jet quenching model within a unified multi-stage framework and demonstrate for the first time a simultaneous description of leading hadrons, inclusive jets, and elliptic flow observables which spans multiple centralities and collision energies. This highlights one of the major successes of the JETSCAPE framework in providing a tool for setting up an effective parton evolution that inc… ▽ More We present a jet quenching model within a unified multi-stage framework and demonstrate for the first time a simultaneous description of leading hadrons, inclusive jets, and elliptic flow observables which spans multiple centralities and collision energies. This highlights one of the major successes of the JETSCAPE framework in providing a tool for setting up an effective parton evolution that includes a high-virtuality radiation dominated energy loss phase (MATTER), followed by a low-virtuality scattering dominated (LBT) energy loss phase. Measurements of jet and charged-hadron $R_{AA}$ set strong constraints on the jet quenching model. Jet-medium response is also included through a weakly-coupled transport description. △ Less

Submitted 17 February, 2020; originally announced February 2020.

Comments: 4 pages, 4 figures, contribution to the Quark Matter 2019 proceedings

Multi-stage evolution of heavy quarks in the quark-gluon plasma

Authors: G. Vujanovic, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, K. Kauder, W. Ke, E. Khalaj, M. Kordell II , et al. (25 additional authors not shown)

Abstract: The interaction of heavy flavor with the quark-gluon plasma (QGP) in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage (and multi-model) evolution of heavy quarks within JETSCAPE provides a cohesive description of heavy flavor quenching inside the QGP. As the parton shower develops… ▽ More The interaction of heavy flavor with the quark-gluon plasma (QGP) in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage (and multi-model) evolution of heavy quarks within JETSCAPE provides a cohesive description of heavy flavor quenching inside the QGP. As the parton shower develops, a model becomes active as soon as its kinematic region of validity is reached. Two combinations of heavy-flavor energy-loss models are explored within a realistic QGP medium, using parameters which were tuned to describe {\it light-flavor} partonic energy-loss. △ Less

Submitted 16 February, 2020; originally announced February 2020.

Comments: 4 pages, 2 figures, contribution to the Quark Matter 2019 proceedings

Revisiting Bayesian constraints on the transport coefficients of QCD

Authors: J. -F. Paquet, A. Angerami, S. A. Bass, S. Cao, Y. Chen, J. Coleman, L. Cunqueiro, T. Dai, L. Du, R. Ehlers, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, Y. He, M. Heffernan, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, K. Kauder, W. Ke, E. Khalaj, M. Kordell II , et al. (25 additional authors not shown)

Abstract: Multistage models based on relativistic viscous hydrodynamics have proven successful in describing hadron measurements from relativistic nuclear collisions. These measurements are sensitive to the shear and the bulk viscosities of QCD and provide a unique opportunity to constrain these transport coefficients. Bayesian analyses can be used to obtain systematic constraints on the viscosities of QCD,… ▽ More Multistage models based on relativistic viscous hydrodynamics have proven successful in describing hadron measurements from relativistic nuclear collisions. These measurements are sensitive to the shear and the bulk viscosities of QCD and provide a unique opportunity to constrain these transport coefficients. Bayesian analyses can be used to obtain systematic constraints on the viscosities of QCD, through methodical model-to-data comparisons. In this manuscript, we discuss recent developments in Bayesian analyses of heavy ion collision data. We highlight the essential role of closure tests in validating a Bayesian analysis before comparison with measurements. We discuss the role of the emulator that is used as proxy for the multistage theoretical model. We use an ongoing Bayesian analysis of soft hadron measurements by the JETSCAPE Collaboration as context for the discussion. △ Less

Submitted 12 February, 2020; originally announced February 2020.

Comments: 4 pages, 1 figure, contribution to the Quark Matter 2019 proceedings

The JETSCAPE framework

Authors: J. H. Putschke, K. Kauder, E. Khalaj, A. Angerami, S. A. Bass, S. Cao, J. Coleman, L. Cunqueiro, T. Dai, L. Du, H. Elfner, D. Everett, W. Fan, R. J. Fries, C. Gale, Y. He, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, W. Ke, M. Kordell II, A. Kumar, T. Luo, A. Majumder , et al. (20 additional authors not shown)

Abstract: The JETSCAPE simulation framework is an overarching computational envelope for developing complete event generators for heavy-ion collisions. It allows for modular incorporation of a wide variety of existing and future software that simulates different aspects of a heavy-ion collision. The default JETSCAPE package contains both the framework, and an entire set of indigenous and third party routine… ▽ More The JETSCAPE simulation framework is an overarching computational envelope for developing complete event generators for heavy-ion collisions. It allows for modular incorporation of a wide variety of existing and future software that simulates different aspects of a heavy-ion collision. The default JETSCAPE package contains both the framework, and an entire set of indigenous and third party routines that can be used to directly compare with experimental data. In this article, we outline the algorithmic design of the JETSCAPE framework, define the interfaces and describe the default modules required to carry out full simulations of heavy-ion collisions within this package. We begin with a description of the various physics elements required to simulate an entire event in a heavy-ion collision, and distribute these within a flowchart representing the event generator and statistical routines for comparison with data. This is followed by a description of the abstract class structure, with associated members and functions required for this flowchart to work. We then define the interface that will be required for external users of JETSCAPE to incorporate their code within this framework and to modify existing elements within the default distribution. We conclude with a discussion of some of the physics output for both $p$-$p$ and $A$-$A$ collisions from the default distribution, and an outlook towards future releases. In the appendix, we discuss various architectures on which this code can be run and outline our benchmarks on similar hardware. △ Less

Submitted 18 March, 2019; originally announced March 2019.

Comments: 93 pages, 13 figures

Exploring the influence of bulk viscosity of QCD on dilepton tomography

Authors: Gojko Vujanovic, Jean-François Paquet, Chun Shen, Gabriel S. Denicol, Sangyong Jeon, Charles Gale, Ulrich Heinz

Abstract: The collective behavior of hadrons and of electromagnetic radiation in heavy-ion collisions has been widely used to study the properties of the the Quark-Gluon Plasma (QGP). Indeed this collectivity, as measured by anisotropic flow coefficients, can be used to constrain the transport properties of QGP. The goal of this contribution is to investigate the influence of the specific bulk viscosity (… ▽ More The collective behavior of hadrons and of electromagnetic radiation in heavy-ion collisions has been widely used to study the properties of the the Quark-Gluon Plasma (QGP). Indeed this collectivity, as measured by anisotropic flow coefficients, can be used to constrain the transport properties of QGP. The goal of this contribution is to investigate the influence of the specific bulk viscosity ($ζ/s$) on dilepton production, both at Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. We explore the sensitivity of dileptons to dynamical features that bulk viscosity induces on the evolution of a strongly-interacting medium, and highlight what makes them a valuable probe in the pursuit to also constrain $ζ/s$. △ Less

Submitted 23 February, 2020; v1 submitted 12 March, 2019; originally announced March 2019.

Comments: 25 pages, 16 figures

Journal ref: Phys. Rev. C 101, 044904 (2020)

Multi-stage jet evolution through QGP using the JETSCAPE framework: inclusive jets, correlations and leading hadrons

Authors: C. Park, A. Angerami, S. A. Bass, S. Cao, J. Coleman, L. Cunqueiro, T. Dai, L. Du, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, Y. He, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, K. Kauder, W. Ke, E. Khalaj, M. Kordell II, A. Kumar, T. Luo, A. Majumder , et al. (19 additional authors not shown)

Abstract: The JETSCAPE Collaboration has recently announced the first release of the JETSCAPE package that provides a modular, flexible, and extensible Monte Carlo event generator. This innovative framework makes it possible to perform a comprehensive study of multi-stage high-energy jet evolution in the Quark-Gluon Plasma. In this work, we illustrate the performance of the event generator for different alg… ▽ More The JETSCAPE Collaboration has recently announced the first release of the JETSCAPE package that provides a modular, flexible, and extensible Monte Carlo event generator. This innovative framework makes it possible to perform a comprehensive study of multi-stage high-energy jet evolution in the Quark-Gluon Plasma. In this work, we illustrate the performance of the event generator for different algorithmic approaches to jet energy loss, and reproduce the measurements of several jet and hadron observables as well as correlations between the hard and soft sector. We also carry out direct comparisons between different approaches to energy loss to study their sensitivity to those observables. △ Less

Submitted 15 February, 2019; originally announced February 2019.

Future physics opportunities for high-density QCD at the LHC with heavy-ion and proton beams

Authors: Z. Citron, A. Dainese, J. F. Grosse-Oetringhaus, J. M. Jowett, Y. -J. Lee, U. A. Wiedemann, M. Winn, A. Andronic, F. Bellini, E. Bruna, E. Chapon, H. Dembinski, D. d'Enterria, I. Grabowska-Bold, G. M. Innocenti, C. Loizides, S. Mohapatra, C. A. Salgado, M. Verweij, M. Weber, J. Aichelin, A. Angerami, L. Apolinario, F. Arleo, N. Armesto , et al. (160 additional authors not shown)

Abstract: The future opportunities for high-density QCD studies with ion and proton beams at the LHC are presented. Four major scientific goals are identified: the characterisation of the macroscopic long wavelength Quark-Gluon Plasma (QGP) properties with unprecedented precision, the investigation of the microscopic parton dynamics underlying QGP properties, the development of a unified picture of particle… ▽ More The future opportunities for high-density QCD studies with ion and proton beams at the LHC are presented. Four major scientific goals are identified: the characterisation of the macroscopic long wavelength Quark-Gluon Plasma (QGP) properties with unprecedented precision, the investigation of the microscopic parton dynamics underlying QGP properties, the development of a unified picture of particle production and QCD dynamics from small (pp) to large (nucleus--nucleus) systems, the exploration of parton densities in nuclei in a broad ($x$, $Q^2$) kinematic range and the search for the possible onset of parton saturation. In order to address these scientific goals, high-luminosity Pb-Pb and p-Pb programmes are considered as priorities for Runs 3 and 4, complemented by high-multiplicity studies in pp collisions and a short run with oxygen ions. High-luminosity runs with intermediate-mass nuclei, for example Ar or Kr, are considered as an appealing case for extending the heavy-ion programme at the LHC beyond Run 4. The potential of the High-Energy LHC to probe QCD matter with newly-available observables, at twice larger center-of-mass energies than the LHC, is investigated. △ Less

Submitted 25 February, 2019; v1 submitted 17 December, 2018; originally announced December 2018.

Comments: 209 pages; Report from Working Group 5 of the Workshop on the Physics of the CERN HL-LHC, and Perspectives at the HE-LHC (v2: Minor updates to text and figures. Added one author.)

Report number: CERN-LPCC-2018-07

Jet substructure modification in a QGP from a multi-scale description of jet evolution with JETSCAPE

Authors: Y. Tachibana, A. Angerami, S. A. Bass, S. Cao, J. Coleman, L. Cunqueiro, T. Dai, L. Du, H. Elfner, D. Everett, W. Fan, R. Fries, C. Gale, Y. He, U. Heinz, B. V. Jacak, P. M. Jacobs, S. Jeon, K. Kauder, W. Ke, E. Khalaj, M. Kordell II, A. Kumar, T. Luo, A. Majumder , et al. (19 additional authors not shown)

Abstract: The modification of jet substructure in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage jet evolution in JETSCAPE provides an integrated description of jet quenching by combining multiple models, with each becoming active at a different stage of the parton shower evolution. Jet s… ▽ More The modification of jet substructure in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage jet evolution in JETSCAPE provides an integrated description of jet quenching by combining multiple models, with each becoming active at a different stage of the parton shower evolution. Jet substructure modification due to different aspects of jet quenching is studied using jet shape and jet fragmentation observables. Various combinations of jet energy loss models are exploed, with medium background provided by (2 + 1)-D VISHNU with TRENTo+freestreaming initial conditions. Results reported here are from simulations performed within JETSCAPE framework. △ Less

Submitted 22 February, 2019; v1 submitted 15 December, 2018; originally announced December 2018.

Comments: 4 pages, 3 figures, Proceedings of Hard Probes 2018, 30 September-5 October, Aix-Les-Bains, France