arXiv subjects

Guang-You Qin

Publications and source records attributed to Guang-You Qin.

At least 37 records · Page 2Linked to original sources

arXiv2024

Flavor Hierarchy of Jet Energy Correlators inside the Quark-Gluon Plasma

Heavy flavor jets provide ideal tools to probe the mass effect on jet substructure in both vacuum and quark-gluon plasma (QGP). Energy-energy correlator (EEC) is an excellent jet substructure observable owning to its strong sensitivity to jet physics at different scales. We perform a complete realistic simulation on medium modification of heavy and light flavor jet EEC in heavy-ion collisions. A clear flavor hierarchy is observed for jet EEC in both vacuum and QGP due to the mass effect. The medium modification of inclusive jet EEC at different angular scales exhibits very rich structure: suppression at intermediate angles, and enhancement at small and large angles, which can be well explained by the interplay of mass effect, energy loss, medium-induced radiation and medium response. These unique features of jet EEC are shown to probe the physics of jet-medium interaction at different scales, and can be readily validated by upcoming experiments.

hep-ph↗

arXiv2024

Spin polarization of $Λ$ hyperons along beam direction in p+Pb collisions at $\sqrt{s_{NN}}=8.16$ TeV using hydrodynamic approaches

We have implemented the 3+1 dimensional CLVisc hydrodynamics model with TRENTO-3D initial conditions to investigate the spin polarization of $Λ$ hyperons along the beam direction in p+Pb collisions at $\sqrt{s_{NN}} = 8.16$ TeV. Following our previous theoretical framework based on quantum kinetic theory, we consider three different scenarios: $Λ$ equilibrium, $s$ quark equilibrium, and iso-thermal equilibrium scenarios. We have computed the second Fourier sine coefficients of spin polarization along the beam direction, denoted as $\left\langle P_{z} \sin 2(ϕ_{p} - Ψ_{2}) \right\rangle$, with $ϕ_{p} - Ψ_{2}$ being the azimuthal angle relative to the second-order event plane $Ψ_{2}$, as functions of multiplicity, transverse momentum and pseudo-rapidity in the three scenarios. Additionally, we have also computed the spin polarization along the beam direction, $P_{z}$, as a function of the azimuthal angle. We find that the spin polarization induced by thermal vorticity always provides an opposite contribution compared to the shear-induced polarization in p+Pb collisions. The total spin polarization computed by the current hydrodynamic model disagrees with the data measured by LHC-CMS experiments. Our findings imply that other non-flow effects may play a crucial role in p+Pb collisions.

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arXiv2024

Reexamining charm versus bottom quark energy loss inside a color-deconfined medium

The general intuition that heavier partons suffer weaker energy loss inside a quark-gluon plasma (QGP) medium is critically re-examined. Within a linear Boltzmann transport model that includes both Yukawa and string types of interactions between heavy quarks and the QGP, we find that while the radiative energy loss is suppressed by the parton mass, heavier partons can experience stronger string potential scatterings with the medium. Their competition may result in less energy loss of bottom quarks than charm quarks at low transverse momentum ($p_\mathrm{T}$) but an inverse order at high $p_\mathrm{T}$. Our model calculation shows a weaker nuclear modification on bottom particles than charm particles at low $p_\mathrm{T}$, as observed by both RHIC and LHC experiments, but predicts an opposite hierarchy at high $p_\mathrm{T}$. A larger momentum space transport coefficient ($\hat{q}$) and a smaller spatial diffusion coefficient ($D_\mathrm{s}$) are found for bottom quarks than for charm quarks.

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arXiv2024

System size and shape dependences of collective flow fluctuations in relativistic nuclear collisions

Quantum fluctuations plays an essential role in forming the collective flow of hadrons observed in relativistic heavy-ion collisions. Event-by-event fluctuations of the collective flow can arise from various sources, such as the fluctuations in the initial geometry, hydrodynamic expansion, hadronization, and hadronic evolution of the nuclear matter, while the exact contribution from each source is still an open question. Using a (3+1)-dimensional relativistic hydrodynamic model coupled to a Monte-Carlo Glauber initial condition, Cooper-Frye particlization and a hadronic transport model, we explore the system size and shape dependences of the collective flow fluctuations in Au+Au, Cu+Au, and O+O collisions at $\sqrt{s_\mathrm{NN}}=200$~GeV. The particle yields, mean transverse momenta, 2-particle and 4-particle cumulant elliptic flows ($v_2\{2\}$ and $v_2\{4\}$) from our calculation agree with the currently existing data from RHIC. Different centrality dependences of the flow fluctuations, quantified by the $v_2\{4\}/v_2\{2\}$ ratio, are found for different collision systems due to their different sizes and shapes. By comparing $v_2\{4\}/v_2\{2\}$ between different hadron species, and comparing $v_2\{4\}/v_2\{2\}$ to the initial state geometric fluctuations quantified by the cumulant eccentricity ratio $\varepsilon_2\{4\}/\varepsilon_2\{2\}$, we find that while the initial state fluctuations are the main source of the $v_2$ fluctuations in large collision systems, other sources like nonlinear hydrodynamic response, hadronization, and hadronic afterburner can significantly affect the $v_2$ fluctuations in small systems.

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arXiv2024

Study of bottom quark dynamics via non-prompt $D^0$ and $J/ψ$ in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV

We study bottom quark energy loss via the nuclear modification factor ($R_\mathrm{AA}$) and elliptic flow ($v_2$) of non-prompt $D^0$ and $J/ψ$ in relativistic heavy-ion collisions at the LHC. The space-time profile of quark-gluon plasma is obtained from the CLVisc hydrodynamics simulation, the dynamical evolution of heavy quarks inside the color deconfined QCD medium is simulated using a linear Boltzmann transport model that combines Yukawa and string potentials of heavy-quark-medium interactions, the hadronization of heavy quarks is performed using a hybrid coalescence-fragmentation model, and the decay of $B$ mesons is simulated via PYTHIA. Using this numerical framework, we calculate the transverse momentum ($p_\mathrm{T}$) dependent $R_\mathrm{AA}$ and $v_2$ of direct $D$ mesons, $B$ mesons, and non-prompt $D^0$ and $J/ψ$ from $B$ meson decay in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV. We find the mass hierarchy of the nuclear modification of prompt $D$ and $B$ mesons depends on their $p_\mathrm{T}$. Both $R_\mathrm{AA}$ and $v_2$ of heavy flavor particles show strong $p_\mathrm{T}$ and centrality dependences due to the interplay between parton energy loss, medium geometry and flow, and hadronization of heavy quarks. Non-prompt $D^0$ and $J/ψ$ share similar patterns of $R_\mathrm{AA}$ and $v_2$ to $B$ mesons except for a $p_\mathrm{T}$ shift during the decay processes. Therefore, future more precise measurements on non-prompt $D^0$ and $J/ψ$ can help further pin down the bottom quark dynamics inside the quark-gluon plasma.

hep-ph↗

arXiv2024

Flavor hierarchy of parton energy loss in quark-gluon plasma from a Bayesian analysis

The quenching of light and heavy flavor hadrons in relativistic heavy-ion collisions probes the color and flavor dependences of parton energy loss through a color-deconfined quark-gluon plasma (QGP), and thus reveals the properties of QCD matter at extremely high density and temperature. By combining a next-to-leading order perturbative QCD calculation of parton production, a general ansatz of parton energy loss functions and parton fragmentation functions, we calculate the nuclear modification of various hadron species -- charged hadrons, $D$ mesons and $B$-decayed $J/ψ$ -- over a wide transverse momentum regime. Comparing our calculations to the experimental data using the Bayesian statistical analysis, we perform a first simultaneous extraction of the energy loss functions of gluons ($g$), light quarks ($q$), charm quarks ($c$) and bottom quarks ($b$) inside the QGP. We find that the average parton energy loss at high energies follows the expected hierarchy of $\langle ΔE_g \rangle > \langle ΔE_q \rangle \sim \langle ΔE_c \rangle > \langle ΔE_b \rangle$, while the parton energy loss distribution can further test the QCD calculations of parton interaction with the dense nuclear matter. We also find that the reduction of experimental uncertainties can significantly improve the precision of the extracted parton energy loss functions inside the QGP.

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arXiv2024

Quenching and flow of charm and bottom quarks via semi-leptonic decay of $D$ and $B$ mesons in Pb+Pb collisions at the LHC

Heavy flavor particles provide important probes of the microscopic structure and thermodynamic properties of the quark-gluon plasma (QGP) produced in high-energy nucleus-nucleus collisions. We study the energy loss and flow of charm and bottom quarks inside the QGP via the nuclear modification factor ($R_\mathrm{AA}$) and elliptic flow coefficient ($v_2$) of their decayed leptons in heavy-ion collisions at the LHC. The dynamical evolution of the QGP is performed using the (3+1)-dimensional viscous hydrodynamics model CLVisc; the evolution of heavy quarks inside the QGP is simulated with our improved Langevin model that takes into account both collisional and radiative energy loss of heavy quarks; the hadronization of heavy quarks is simulated via our hybrid coalescence-fragmentation model; and the semi-leptonic decay of $D$ and $B$ mesons is simulated via PYTHIA. By using the same spatial diffusion coefficient for charm and bottom quarks, we obtain smaller $R_\mathrm{AA}$ and larger $v_2$ of charm decayed leptons than bottom decayed leptons, indicating stronger energy loss of charm quarks than bottom quarks inside the QGP within our current model setup.

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arXiv2024

Charmed hadron chemistry and flow in heavy and light ion collisions at the LHC

We study the charmed meson and baryon production and elliptic flow in ultra-relativistic nucleus-nucleus collisions at the LHC energies. The space-time evolution of quark-gluon plasma (QGP) produced in these energetic collisions is obtained via the (3+1)-dimensional CLVisc hydrodynamics model, the heavy quark dynamics inside the QGP is simulated using an improved Langevin model that incorporates both elastic and inelastic parton energy loss processes, and the heavy quark hadronization is simulated utilizing a comprehensive coalescence-fragmentation model. Using our combined approach, we first calculate charmed hadron ratios, $Λ_c/D^0$ and $D_s/D^0$, as well as their elliptic flow ($v_2$) as a function of transverse momentum ($p_T$) for different centralities in Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$~TeV. Due to strangeness enhancement and parton coalescence effects, $D_s/D^0$ and $Λ_c/D^0$ ratios increase from peripheral to central collisions, and such centrality dependence for $Λ_c/D^0$ is stronger than $D_s/D^0$. We further predict the $p_T$ and centrality dependences of charmed hadron chemistry and $v_2$ in smaller Xe+Xe, Ar+Ar and O+O collisions at the LHC energies. Strong centrality and system size dependences for $Λ_c/D^0$ and $D_s/D^0$ ratios are observed across four collision systems. As for charmed hadron flow, both system size and collision geometry are important to understand the centrality dependence of $v_2$ in different collision systems. Our study provides a significant reference for studying heavy quark evolution and hadronizaiton in large and small systems in relativistic nuclear collisions.

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arXiv2024

Anisotropic flow, flow fluctuation and flow decorrelation in relativistic heavy-ion collisions: the roles of sub-nucleon structure and shear viscosity

We study the transverse momentum ($p_T$) differential anisotropic flow and flow fluctuation in Pb+Pb collisions at $\sqrt{s_{NN}}$=5.02 TeV at the LHC. A (3+1)-dimensional CLVisc hydrodynamics framework with fluctuating TRENTO (or AMPT) initial conditions is utilized to simulate the space-time evolution of the quark-gluon plasma (QGP) medium. The effects of shear viscosity and the sub-nucleon structure on anisotropic flow and flow fluctuation are analyzed. Our result shows that shear viscosity tends to suppress both flow coefficients (${v_2\{2}\}$, ${v_2\{4\}}$, ${\langle v_2\rangle}$) and flow fluctuation (${σ_{v_2}}$) due to its smearing effect on local density fluctuation. The flow coefficients appear to be insensitive to the sub-nucleon structure, whereas for flow fluctuation ${σ_{v_2}}$, it tends to be suppressed by the sub-nucleon structure in central collisions but enhanced in peripheral collisions. After taking into account the sub-nucleon structure effect, our numerical result can quantitatively describe the relative flow fluctuations (${v_2\{4\}/v_2\{2\}}$, $F({v_2})$) measured by the ALICE Collaboration at the LHC. We further investigate the effects of shear viscosity, sub-nucleon structure and initial condition model on the flow angle and flow magnitude decorrelations (${A_2^f}$, ${M_2^f}$) using the four-particle correlation method. We find that the flow decorrelation effect is typically stronger in central collisions than in peripheral collisions. The flow angle decorrelation is found to be insensitive to the shear viscosity and sub-nucleon structure, whereas the flow magnitude decorrelation shows quite different behavior when using TRENTO or AMPT initial condition model. Our study sheds light on the anisotropic flow, transport properties and initial structure of the QGP created in high-energy nuclear collisions.

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arXiv2023

Global and local polarization of $Λ$ hyperons across RHIC-BES energies

We report our recent study on the global and local polarization of $Λ$ hyperons in Au+Au collisions at RHIC-BES energies within the (3+1)-dimensional CLVisc hydrodynamics framework. We present our numerical results for the global polarization as the function of collision energies and the local polarization along the beam direction as functions of azimuthal angle in $20-50$% centrality at $\sqrt{s_{NN}}$=7.7 GeV Au+Au collision energy. We have discussed the effects of initial conditions, Spin Hall effect and baryon diffusion.

nucl-th↗

arXiv2023

Constraining the equation of state with heavy quarks in the quasi-particle model of QCD matter

In a quasi-particle model of QCD matter at finite temperature with thermal masses for quarks and gluons from hard thermal loops, the equation of state (EOS) can be described by an effective temperature dependence of the strong coupling $g(T)$. Assuming the same effective coupling between the exchanged gluon and thermal partons, the EOS can also be related to parton energy loss.} Based on the quasi-particle linear Boltzmann transport (QLBT) model coupled to a (3+1)-dimensional viscous hydrodynamic model of the quark-gluon plasma (QGP) evolution and a hybrid fragmentation-coalescence model for heavy quark hadronization, we perform a Bayesian analysis of the experimental data on $D$ meson suppression $R_{\rm AA}$ and anisotropy $v_2$ at RHIC and the LHC. We achieve a simultaneous constraint on the QGP EOS and the heavy quark transport coefficient, both consistent with the lattice QCD results.

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arXiv2023

Unraveling Gluon Jet Quenching through $J/ψ$ Production in Heavy-Ion Collisions

Jet quenching has long been regarded as one of the key signatures for the formation of quark-gluon plasma in heavy-ion collisions. Despite significant efforts, the separate identification of quark and gluon jet quenching has remained as a challenge. Here we show that $J/ψ$ in high transverse momentum ($p_\text{T}$) region provides a uniquely sensitive probe of in-medium gluon energy loss since its production at high $p_\text{T}$ is particularly dominated by gluon fragmentation. Such gluon-dominance is first demonstrated for the baseline of proton-proton collisions within the framework of leading power NRQCD factorization formalism. We then use the linear Boltzmann transport model combined with hydrodynamics for the simulation of jet-medium interaction in nucleus-nucleus collisions. The satisfactory description of experimental data on both nuclear modification factor $R_{\text{AA}}$ and elliptic flow $v_2$ reveals, for the first time, that the gluon jet quenching is the driving force for high $p_\text{T}$ $J/ψ$ suppression. This novel finding is further confirmed by the data-driven Bayesian analyses of relevant experimental measurements, from which we also obtain the first quantitative extraction of the gluon energy loss distribution in the quark-gluon plasma.

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arXiv2023

Medium Response and Jet-Hadron Correlations in Relativistic Heavy-Ion Collisions

High-energy heavy-ion collisions at the Relativistic Heavy-Ion Collider and the Large Hadron Collider have evolved from qualitative understanding into precise extraction of the properties of the Quantum Chromodynamics medium at extremely high temperature. Jet quenching has offered unique insights into the transport properties of the Quark-Gluon Plasma (QGP) created in these energetic collisions. Apart from medium modification of jets, jet-induced medium excitation constitutes another crucial aspect of jet-QGP interaction, and is indispensable in understanding the soft components of jets. We review recent theoretical and phenomenological developments on medium response to jet energy loss, including an overview of both weakly and strongly coupled approaches for describing the thermalization and propagation of energy deposition from jets, effects of medium response on jet observables, and exploration of its unique signatures in jet-hadron correlations. Jet-induced medium excitation is shown to be an essential component in probing the in-medium dynamics of jets and a critical step towards precise extraction of the QGP properties.

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arXiv2023

Probing vortical structures in heavy-ion collisions at RHIC-BES energies through helicity polarization

We investigate the hydrodynamic helicity polarization of $Λ$ hyperons, defined as the projection of the spin polarization vector along the directions of particle momenta, at RHIC-BES energies by utilizing the relativistic (3+1)D CLVisc hydrodynamics framework with SMASH initial conditions. As opposed to local spin polarization at high energy collisions, our hydrodynamic simulations demonstrate that the helicity polarization induced by the kinetic vorticity dominates over other contributions at intermediate and low collision energies. Our findings provide an opportunity to probe the fine structure of local kinetic vorticity as a function of azimuthal angle at intermediate and low collision energies by mapping our predictions to the future measurements in experiments.

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arXiv2022

Enhancement of baryon-to-meson ratios around jets as a signature of medium response

We present a unique signal of jet-induced medium excitations: the enhancement of baryon-to-meson ratios around the quenched jets.To illustrate this, we study jet-particle correlations and the distributions of jet-induced identified particles with respect to the jet direction in Pb+Pb collisions at the LHC via a multi-phase transport model.We find a strong enhancement of baryon-to-meson ratios for associated particles at intermediate transverse momentum around the triggered jets in Pb+Pb collisions relative to p+p collisions, due to the coalescence of jet-excited medium partons.Since the lost energy from jets can diffuse to large angles, such baryon-to-meson-ratio enhancement is more pronounced for larger relative distance from the jet axis.We argue that the experimental confirmation of the enhancement of jet-induced baryon-to-meson ratios around the jets will provide an unambiguous evidence for the medium response to jet quenching in heavy-ion collisions.

hep-ph↗

arXiv2022

Deep-learning quasi-particle masses from QCD equation of state

The interactions of quarks and gluons are strong at non-perturbative region. The equation of state (EoS) of a strongly-interacting quantum chromodynamics (QCD) medium can only be studied using the first-principle lattice QCD calculations. However, the complicated QCD EoS can be reproduced using simple statistical formula by treating the medium as a free parton gas whose fundamental degree of freedoms are dressed quarks and gluons called quasi-particles, with temperature-dependent masses. We use deep neural network and auto differentiation to solve this variational problem in which the masses of quasi gluons, up/down and strange quarks are three unknown functions, whose forms are represented by deep neural network. We reproduce the QCD EoS using these machine learned quasi-particle masses, and calculate the shear viscosity over entropy density ($η/s$) as a function of temperature of the hot QCD matter.

hep-ph↗

arXiv2022

Local and global polarization of $Λ$ hyperons across RHIC-BES energies: the roles of spin hall effect, initial condition and baryon diffusion

We perform a systematic study on the local and global spin polarization of $Λ$ and $\overlineΛ$ hyperons in relativistic heavy-ion collisions at beam energy scan energies via the (3+1)-dimensional CLVisc hydrodynamics model with AMPT and SMASH initial conditions. Following the quantum kinetic theory, we decompose the polarization vector as the parts induced by thermal vorticity, shear tensor and the spin Hall effect (SHE). We find that the polarization induced by SHE and the total polarization strongly depends on the initial conditions. At $7.7$GeV, SHE gives a sizeable contribution and even flips the sign of the local polarization along the beam direction for AMPT initial condition, which is not observed for SMASH initial condition. Meanwhile, the local polarization along the out-of-plane direction induced by SHE with AMPT initial condition does not always increase with decreasing collision energies. Next, we find that the polarization along the beam direction is sensitive to the baryon diffusion coefficient, but the local polarization along the out-of-plane direction is not. Our results for the global polarization of $Λ$ and $\overlineΛ$ agree well with the STAR data. Interestingly, the global polarization of $\overlineΛ$ is not always larger than that of $Λ$ due to various competing effects. Our findings are helpful for understanding the polarization phenomenon and the detailed structure of quark-gluon plasma in relativistic heavy-ion collisions.

hep-ph↗

arXiv2022

(3+1)-D viscous hydrodynamics CLVisc at finite net baryon density: identified particle spectra, anisotropic flows and flow fluctuations across BES energies

To study the bulk properties of the quark-gluon-plasma (QGP) produced at the beam energy scan (BES) energies at the Relativistic Heavy Ion Collider (RHIC), we extend the (3+1)-dimensional viscous hydrodynamics CLVisc to include net baryon number conservation and Israel-Stewart-like equation for baryon diffusion with the NEOS-BQS equation of state, fluctuating initial conditions from Monte-Carlo Glauber model, and the afterburner SMASH. This integrated framework is shown to provide a good description of identified particle spectra, mean transverse momenta and anisotropic flows for different centralities and over a wide range of collision energies (7.7-62.4 GeV). It is found that the mean momenta of identified particles and anisotropic flows increases mildly with the collision energy due to larger radial flow. We further compute the multiple-particle cumulant ratio $v_2\{4\}/v_2\{2\}$ of elliptic flow across BES energies, and find that the relative fluctuations of elliptic flow are insensitive to the collision energy, consistent with the preliminary STAR data. Our model provides a benchmark for understanding the RHIC-BES data and studying the critical properties and phase structure of hot and dense QCD matter.

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