With the use of martini, a model which considers evolving QCD jets against a fluid dynamical background, it is shown that the introduction of formation time to the parton shower after the initial hard scattering is essential for a simultaneous description of charged hadron and jet <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>R</mi><mrow><mi>A</mi><mi>A</mi></mrow></msub></math>. This inclusion also improves jet shape ratios at small angle and jet fragmentation function ratios of leading charged hadrons. The martini framework is then aimed at a study of the leading-order, next-to-leading-order, and nonperturbative collision kernels. Sizable differences in the modification of jet substructure observables, i.e., jet shape and fragmentation functions, are observed. Such differences are caused by the difference in the radiation rates of relatively soft gluons that survive in the evolution in medium.

Canada

Rouzbeh Modarresi-Yazdi

United States

China

Shuzhe Shi

Charles Gale

Sangyong Jeon

QCD jets in a hot and dense medium: A study of shower formation time and collision kernels

The attractor, which is supposed to be one of the possible answers for the early applicability of hydrodynamics in the evolution with different initial conditions, has attracted great attention to the fast decreasing of degrees of freedom in heavy ion collisions. We find attractor behaviors for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>1</mn><mo>+</mo><mn>1</mn><mi mathvariant="normal">D</mi></mrow></math> viscous hydrodynamics with general rapidity distribution based on Müller-Isreal-Stewart theory. Meanwhile, we also observe that a rapid expansion in the fluid velocity is essential for a rapid early time attractor.

Shile Chen

Attractor for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>(</mo><mn>1</mn><mo>+</mo><mn>1</mn><mo>)</mo><mi mathvariant="normal">D</mi></mrow></math> viscous hydrodynamics with general rapidity distribution

The possible link between entanglement and thermalization, and the dynamics of hadronization are addressed by studying the real-time response of the massive Schwinger model coupled to external sources. This setup mimics the production and fragmentation of quark jets, as the Schwinger model and quantum chromodynamics (QCD) share the properties of confinement and chiral symmetry breaking. By using simulations of quantum dynamics on classical hardware, we study the entanglement between the produced jets, and observe the growth of the corresponding entanglement entropy in time. This growth arises from the increased number of contributing eigenstates of the reduced density matrix with sufficiently large and close eigenvalues. We also investigate the physical nature of these eigenstates, and find that at early times they correspond to fermionic Fock states. We then observe the transition from these fermionic Fock states to mesonlike bound states as a function of time. In other words, we observe how hadronization develops in real time. At late times, the local observables at midrapidity (such as the fermion density and the electric field) approach approximately constant values, suggesting the onset of equilibrium and approach to thermalization.

Adrien Florio

David Frenklakh

Kazuki Ikeda

Dmitri Kharzeev

Vladimir Korepin

Kwangmin Yu

Quantum real-time evolution of entanglement and hadronization in jet production: Lessons from the massive Schwinger model

Using quantum simulations on classical hardware, we study the phase diagram of the massive Schwinger model with a <math><mi>θ</mi></math> term at finite chemical potential <math><mi>μ</mi></math>. We find that the quantum critical point in the phase diagram of the model can be detected through the entanglement entropy and entanglement spectrum. As a first step, we chart the phase diagram using conventional methods by computing the dependence of the charge and chiral condensates on the fermion mass <math><mi>m</mi></math>, coupling constant <math><mi>g</mi></math>, and the chemical potential <math><mi>μ</mi></math>. At zero density, the Schwinger model possesses a quantum critical point at <math><mi>θ</mi><mo>=</mo><mi>π</mi></math> and <math><mrow><mi>m</mi><mo>/</mo><mi>g</mi><mo>≃</mo><mn>0.33</mn></mrow></math>. We find that the position of this quantum critical point depends on the chemical potential. Near this quantum critical point, we observe a sharp maximum in the entanglement entropy. Moreover, we find that the quantum critical point can be located from the entanglement spectrum by detecting the position of the gap closing point.

Dmitri E. Kharzeev

Germany

René Meyer

Detecting the critical point through entanglement in the Schwinger model

The chiral magnetic wave (CMW) is a macroscopic quantum phenomenon that arises due to the mixing of the electric and chiral charge oscillations induced by the chiral anomaly. In this study we report the first quantum simulation (on classical hardware) of the real-time dynamics of CMWs in the Schwinger model. Our quench protocol is the following; at <math><mi>t</mi><mo>=</mo><mn>0</mn></math> we suddenly place an electric dipole at the middle of our lattice. Due to chiral anomaly, this dipole excites the CMW that propagates towards the edges of the lattice. In the Schwinger model tuned to the conformal critical point (at <math><mi>θ</mi><mo>=</mo><mi>π</mi></math>, <math><mi>m</mi><mo>/</mo><mi>g</mi><mo>≃</mo><mn>0.2</mn></math>), we find a gapless linear CMW that propagates with the speed of light. For a massless Schwinger model (<math><mrow><mi>θ</mi><mo>=</mo><mn>0</mn></mrow></math>, <math><mrow><mi>m</mi><mo>=</mo><mn>0</mn></mrow></math>), we find a gapped linear CMW, in accord with previous analytical analyses. For a massive Schwinger model (that is dual to strongly interacting bosonic theory), we enter the new regime of nonlinear CMWs, where we find a surprise. Specifically, for <math><mi>m</mi><mo>/</mo><mi>g</mi><mo>&gt;</mo><mn>1</mn></math>, the frequency of electric charge oscillations becomes much smaller than the frequency of the oscillations of the chiral charge. For <math><mi>m</mi><mo>/</mo><mi>g</mi><mo>=</mo><mn>4</mn></math>, we find a solution corresponding to a nearly static electric dipole with fast oscillations of the chiral charge confined within. We call this solution a “thumper” and study its properties in detail. We speculate that thumpers might be relevant for CMWs in the strange quark sector of quark-gluon plasma and narrow gap semiconductors.

Nonlinear chiral magnetic waves

The production of jets should allow testing the real-time response of the QCD vacuum disturbed by the propagation of high-momentum color charges. Addressing this problem theoretically requires a real-time, nonperturbative method. It is well known that the Schwinger model [QED in (<math><mrow><mn>1</mn><mo>+</mo><mn>1</mn></mrow></math>) dimensions] shares many common properties with QCD, including confinement, chiral symmetry breaking, and the existence of vacuum fermion condensate. As a step in developing such an approach, we report here on fully quantum simulations of a massive Schwinger model coupled to external sources representing quark and antiquark jets as produced in <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> annihilation. We study, for the first time, the modification of the vacuum chiral condensate by the propagating jets and the quantum entanglement between the fragmenting jets. Our results indicate strong entanglement between the fragmentation products of the two jets at rapidity separations <math><mi>Δ</mi><mi>η</mi><mo>≤</mo><mn>2</mn></math>, which can potentially exist also in QCD and can be studied in experiments.

Real-Time Nonperturbative Dynamics of Jet Production in Schwinger Model: Quantum Entanglement and Vacuum Modification

The collective properties of final state hadrons produced in the high statistics $$_{44}^{96}$$ <math> <msubsup> <mrow></mrow> <mrow> <mn>44</mn> </mrow> <mn>96</mn> </msubsup> </math> Ru + $$_{44}^{96}$$ <math> <msubsup> <mrow></mrow> <mrow> <mn>44</mn> </mrow> <mn>96</mn> </msubsup> </math> Ru and $$_{40}^{96}$$ <math> <msubsup> <mrow></mrow> <mrow> <mn>40</mn> </mrow> <mn>96</mn> </msubsup> </math> Zr + $$_{40}^{96}$$ <math> <msubsup> <mrow></mrow> <mrow> <mn>40</mn> </mrow> <mn>96</mn> </msubsup> </math> Zr collisions at $$\sqrt{s_\textrm{NN}} = 200~\textrm{GeV}$$ <math> <mrow> <msqrt> <msub> <mi>s</mi> <mtext>NN</mtext> </msub> </msqrt> <mo>=</mo> <mn>200</mn> <mspace width="3.33333pt"></mspace> <mtext>GeV</mtext> </mrow> </math> are found to be significantly different. Such differences were argued to be precise probes of the difference in nucleon distribution in the isobar nuclei. We investigate the $$J/\psi $$ <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math> production in the isobar collision via a relativistic transport approach. By comparing the isobar systems according to equal centrality bin and equal multiplicity bin, we find that the yield ratio of $$J/\psi $$ <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math> is sensitive to the differences in both the number of binary collisions and the medium evolution. Besides, the elliptic flow $$v_2$$ <math> <msub> <mi>v</mi> <mn>2</mn> </msub> </math> of $$J/\psi $$ <math> <mrow> <mi>J</mi> <mo>/</mo> <mi>ψ</mi> </mrow> </math> is qualitatively different from the light hadrons, and the ratio between Ru + Ru and Zr + Zr collisions is sensitive to the medium evolution. The charmonium production provides an independent probe to study the nucleon distribution in the isobar system.

France

Jiaxing Zhao

Detecting nuclear mass distribution in isobar collisions via charmonium

Jets produced by the initial hard scattering in heavy ion collision events lose energy due to interactions with the color-deconfined medium formed around them: The quark-gluon plasma (QGP). Jet-medium interactions constitute an important theoretical and experimental field for studies of QGP, and various models with different assumptions have been proposed to describe them. A fair and direct comparison of these models requires that all other aspects of the simulation be fixed, which is achieved in this work by relying on the jetscape framework. We employ jetscape to directly and comprehensively compare two successful energy loss models: cujet and martini. We compare the models with the results of measurements of jet spectra and substructure observables. With the strong coupling tuned separately, we find that the two models broadly agree with each other in nuclear modification factors for charged hadrons and jets with cone size <math><mrow><mi>R</mi><mo>=</mo><mn>0.4</mn></mrow></math>. Systematic differences are reported in fragmentation functions, jet shape, and cone-size dependent jet <math><msub><mi>R</mi><mrow><mi>A</mi><mi>A</mi></mrow></msub></math>.

Rouzbeh Modarresi Yazdi

Comparing the martini and cujet models for jet quenching: Medium modification of jets and jet substructure

The magnetic fields in heavy-ion collisions are important ingredients for many interesting phenomena, such as the chiral magnetic effect, the chiral magnetic wave, the directed flow <math><msub><mi>v</mi><mn>1</mn></msub></math> of <math><msup><mi>D</mi><mn>0</mn></msup></math> mesons, and the splitting of the spin polarization of the <math><mi>Λ</mi><mo>/</mo><mover><mi>Λ</mi><mo>¯</mo></mover></math>. Quantitative studies of these phenomena, however, suffer from limited understanding of the dynamical evolution of these fields in the medium created by the collisions, which remains a critical and challenging problem. The initial magnetic fields from the colliding nuclei decay very fast in the vacuum but their lifetime could be extended through medium response due to electrically conducting quarks and antiquarks. Here we perform a detailed analysis of such medium effect on the dynamical magnetic fields by numerically solving Maxwell's equations concurrently with the expanding medium described by viscous hydrodynamics, under the assumption of negligible back reaction of the fields on the fluid evolution. Our results suggest a considerable enhancement of late time magnetic fields, the magnitude of which depends sensitively on the fireball expansion as well as the medium electric conductivity both before and during hydrodynamic stage.

Anping Huang

Duan She

Mei Huang

Jinfeng Liao

Dynamical magnetic fields in heavy-ion collisions

Gauge fields provide the fundamental interactions in the Standard Model of particle physics. Gauge field configurations with nontrivial topological windings are known to play crucial roles in many important phenomena, from matter-antimatter asymmetry of today’s universe to spontaneous chiral symmetry breaking in strong interaction. Their presence is, however, elusive for direct detection in experiments. Here we show that measurements of the chiral magnetic effect (CME) in heavy ion collisions can be used for accessing the topological fluctuations of the non-Abelian gauge fields in the quantum chromodynamics (QCD). To achieve this, we implemented a key ingredient, the stochastic dynamics of gauge field topological fluctuations, into a state-of-the-art framework for simulating the CME in these collisions. This new framework provides the necessary tool to quantify initial topological fluctuations from any definitive CME signal to be extracted from experimental data. It also reveals a universal scaling relation between initial topological fluctuations and particle multiplicity produced in the corresponding collision events.