arXiv subjects

Huan Zhong Huang

Publications and source records attributed to Huan Zhong Huang.

At least 19 recordsLinked to original sources

arXiv2026

Probing Jet-Medium Interactions in Heavy-Ion Collisions Using Energy-Energy Correlators

Energy-energy correlators (EECs) provide a sensitive probe of both perturbative and nonperturbative dynamics in relativistic heavy-ion collisions. Jet-medium interactions enhance particle multiplicity within the jet cone, which must be properly accounted for when extracting the EEC of jet shower hadrons in experiments. To address this issue, we develop an augmentation method that exploits momentum conservation between the near-side and away-side regions, using $γ$-jet events with 0-10\% centrality in Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV simulated with the CoLBT-hydro model. This approach yields an experimentally reconstructed EEC that shows improved agreement with the EEC of hadrons originating primarily from jet parton splittings. Comparing EECs of jets from Pb+Pb and p+p collisions with different matching conditions can be sensitive to jet medium interaction dynamics, and provide a novel means to test the scenario of jet energy loss in the QGP, followed by fragmentations outside the QGP.

nucl-th↗

arXiv2025

Contrasting Features of Parton Energy Loss in Heavy-ion Collisions at RHIC and the LHC

Energetic quarks and gluons lose energy as they traverse the hot and dense medium created in high-energy heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). The nuclear modification factor ($R_{AA}$) of leading particles quantifies parton energy loss in such collisions, with the particle spectrum in $p+p$ collisions as a reference. Previous $R_{AA}$ measurements at RHIC energies have revealed an approximately constant trend at high transverse momenta ($p_{T}$), implying a scenario where parton energy loss, $Δp_{T}$, scales proportionally with $p_{T}$, a feature naively expected from energy loss dynamics in elastic collisions. In this study, we investigate the LHC $R_{AA}$ measurements which exhibit a pronounced $p_{T}$ dependence of $R_{AA}$ for various particle species, and our analysis attributes this behavior to $Δp_T$ being approximately proportional to $\sqrt{p_{T}}$. These distinct features are consistent with model calculations of dominant radiative energy loss dynamics at the LHC, in contrast to the dominance of collisional energy loss at RHIC. Additionally, the linear increase of fractional energy loss with medium density at different $p_{T}$ magnitudes affirms the previous empirical observation that the magnitude of the energy loss depends mostly on the initial entropy density, with no significant path-length dependence. Implications on the dynamical scenarios of parton energy loss and future experimental investigations will also be discussed.

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arXiv2024

Mini-jet Clustering Algorithm Using Transverse-momentum Seeds in High-energy Nuclear Collisions

We propose an algorithm to detect mini-jet clusters in high-energy nuclear collisions, by selecting a high-transverse-momentum ($p_T$) particle as a seed and assigning a clustering radius ($R$) in the pseudorapidity and azimuthal-angle space. Our PYTHIA simulations for $p$+$p$ collisions show that a scheme with a seeding $p_T$ of around 0.5 GeV/$c$ and $R$ of approximately 0.6 satisfactorily identifies mini-jet clusters. The correlation between clusters obtained in PYTHIA calculations using the algorithm exhibits the proper behavior of hard-scattering-like processes, suggesting its usefulness in isolating mini-jet-like clusters from non-hard-scattering soft processes when applied to actual nuclear-collision data, thereby allowing a closer examination of both the mini-jet and the soft mechanisms.

physics.data-an↗

arXiv2024

Dense Nuclear Matter Equation of State from Heavy-Ion Collisions

The nuclear equation of state (EOS) is at the center of numerous theoretical and experimental efforts in nuclear physics. With advances in microscopic theories for nuclear interactions, the availability of experiments probing nuclear matter under conditions not reached before, endeavors to develop sophisticated and reliable transport simulations to interpret these experiments, and the advent of multi-messenger astronomy, the next decade will bring new opportunities for determining the nuclear matter EOS, elucidating its dependence on density, temperature, and isospin asymmetry. Among controlled terrestrial experiments, collisions of heavy nuclei at intermediate beam energies (from a few tens of MeV/nucleon to about 25 GeV/nucleon in the fixed-target frame) probe the widest ranges of baryon density and temperature, enabling studies of nuclear matter from a few tenths to about 5 times the nuclear saturation density and for temperatures from a few to well above a hundred MeV, respectively. Collisions of neutron-rich isotopes further bring the opportunity to probe effects due to the isospin asymmetry. However, capitalizing on the enormous scientific effort aimed at uncovering the dense nuclear matter EOS, both at RHIC and at FRIB as well as at other international facilities, depends on the continued development of state-of-the-art hadronic transport simulations. This white paper highlights the essential role that heavy-ion collision experiments and hadronic transport simulations play in understanding strong interactions in dense nuclear matter, with an emphasis on how these efforts can be used together with microscopic approaches and neutron star studies to uncover the nuclear EOS.

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arXiv2023

Event Shape Selection Method in Search of the Chiral Magnetic Effect in Heavy-ion Collisions

The search for the chiral magnetic effect (CME) in heavy-ion collisions has been impeded by the significant background arising from the anisotropic particle emission pattern, particularly elliptic flow. To alleviate this background, the event shape selection (ESS) technique categorizes collision events according to their shapes and projects the CME observables to a class of events with minimal flow. In this study, we explore two event shape variables to classify events and two elliptic flow variables to regulate the background. Each type of variable can be calculated from either single particles or particle pairs, resulting in four combinations of event shape and elliptic flow variables. By employing a toy model and the realistic event generator, event-by-event anomalous-viscous fluid dynamics (EBE-AVFD), we discover that the elliptic flow of resonances exhibits correlations with both the background and the potential CME signal, making the resonance flow unsuitable for background control. Through the EBE-AVFD simulations of Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV with various input scenarios, we ascertain that the optimal ESS strategy for background control entails utilizing the single-particle elliptic flow in conjunction with the event shape variable based on particle pairs.

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arXiv2023

Study of Baryon Number Transport Dynamics and Strangeness Conservation Effects Using $Ω$-hadron Correlations

In nuclear collisions at RHIC energies, an excess of $Ω$ hyperons over $\barΩ$ is observed, indicating that $Ω$ carries a net baryon number despite $s$ and $\bar{s}$ quarks being produced in pairs. The baryon number in $Ω$ could have been transported from the incident nuclei and/or produced in baryon-pair production of $Ω$ with other types of anti-hyperons, such as $\barΞ$. To investigate these two scenarios, we propose to measure correlations between $Ω$ and $K$, as well as between $Ω$ and anti-hyperons. We will use two versions, the default and string-melting, of a multiphase transport (AMPT) model to illustrate the method to measure the correlation and to demonstrate the general shape of the correlation. We will present the $Ω$-hadron correlations from simulated $\mathrm{Au}$+$\mathrm{Au}$ collisions at $\sqrt{s_{NN}} = 7.7$ and $14.6 \ \mathrm{GeV}$, and discuss the dependence on collision energy and on the hadronization scheme in these two AMPT versions. These correlations can be used to explore the mechanism of baryon number transport and the effects of baryon number and strangeness conservation in nuclear collisions.

hep-ph↗

arXiv2023

Fourier coefficients of noninterdependent collective motions in heavy-ion collisions

We present a scenario in heavy-ion collisions where different modes of collective motions are noninterdependent, driven by factorized actions in the created nuclear medium. Such physics mechanisms could each dominate at a distinct evolution stage, or coexist simultaneously. If the probability of particle emission is modulated by each nondependent collective motion with a single-harmonic Fourier expansion, the particle azimuthal distribution should be the product of all these expansions. Consequently, nonleading cross terms between collectivity modes appear, and their contributions to experimental observables could be significant. In particular, we argue that the chiral magnetic effect (CME) and elliptic flow can develop separately, with their convolution affecting the observable that is sensitive to the shear-induced CME. We will use the event-by-event anomalous-viscous fluid dynamics model to illustrate the effects of this scenario. Besides giving insights into searches for the CME, we also propose feasible experimental tests based on conventional flow harmonics, and demonstrate the emergence of nonleading cross terms with a multiphase transport model.

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arXiv2023

Dynamic Calculations of Magnetic Field and Implications on Spin Polarization and Spin Alignment in Heavy Ion Collisions

Magnetic field plays a crucial role in various novel phenomena in heavy-ion collisions. We solve the Maxwell equations numerically in a medium with time-dependent electric conductivity by using the Finite-Difference Time-Domain (FDTD) algorithm. We investigate the time evolution of magnetic fields in two scenarios with different electric conductivities at collision energies ranging from $\sqrt{s_\text{NN}}=$ 7.7 to 200 GeV. Our results suggest that the magnetic field may not persist long enough to induce a significant splitting between the global spin polarizations of $Λ$ and $\barΛ$ at freeze-out stage. However, our results do not rule out the possibility of the magnetic field influencing the spin (anti-)alignment of vector mesons.

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arXiv2023

Collective Excitation in High-Energy Nuclear Collisions -- In Memory of Professor Lianshou Liu

We celebrate the legacies of our friend and mentor Professor Lianshou Liu who was one of the pioneers for the phenomenology of multi-particle interactions and initiated the physics of relativistic heavy-ion collisions in China. In this article, we discuss some of the recent exciting experimental observations on the collective phenomena including collectivity, chirality, criticality, strangeness production, and thermal equilibrium in high-energy nuclear collisions. Future directions, especially the physics at high baryon density, will be discussed with a focus on the first-order phase boundary and hyperon-nucleon interactions.

nucl-ex↗

arXiv2022

Baryon Number Transport, Strangeness Conservation and $Ω$-hadron Correlations

Although strange quarks are produced in $s\bar{s}$ pairs, the ratio of $Ω^{-}$ to ${\barΩ}^{+}$ is greater than one in heavy-ion collisions at lower RHIC energies. Thus the produced $Ω$ hyperons must carry net baryon quantum numbers from the colliding nuclei. We present results of $K$-$Ω$ correlations from AMPT model simulations of Au+Au collisions at $\sqrt{s_{NN}}$ = 14.6 GeV, to probe dynamics for baryon number transport to mid-rapidities at this beam energy. We use both the default and string-melting versions to illustrate how hadronization schemes of quark coalescence and string fragmentations could leave imprints on such correlations. Implications on the measurements of these correlations with the STAR experiment at RHIC will also be discussed.

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arXiv2022

Flow-plane decorrelations in heavy-ion collisions with multiple-plane cumulants

The azimuthal correlations between local flow planes at different (pseudo)rapidities ($η$) may reveal important details of the initial nuclear matter density distributions in heavy-ion collisions. Extensive experimental measurements of a factorization ratio ($r_2$) and its derivative ($F_2$) have shown evidence of the longitudinal flow-plane decorrelation. However, nonflow effects also affect this observable and prevent a quantitative understanding of the phenomenon. In this paper, to distinguish decorrelation and nonflow effects, we propose a new cumulant observable, $T_2$, which largely suppresses nonflow. The technique sensitivity to different initial-state scenarios and nonflow effects are tested with a simple Monte Carlo model, and in the end, the method is applied to events simulated by a multiphase transport model (AMPT) for Au+Au collisions at $\sqrt{s_{\rm NN}} =200$ GeV. We also emphasize that a distinct decorrelation signal requires not only the right sign of an observable, but also its proper dependence on the $η$-window of the reference flow plane, to be consistent with the pertinent decorrelation picture.

nucl-ex↗

arXiv2022

Global spin polarization of multistrange hyperons and feed-down effect in heavy-ion collisions

Global spin polarization of hyperons is an important observable to probe the vorticity of the quark-gluon plasma produced in heavy-ion collisions. We calculate the global polarizations of $Λ$, $Ξ^-$, and $Ω^-$ in Au+Au collisions at energies $\sqrt{s_\text{NN}}=$ 7.7--200 GeV based on a multiphase transport model. Our calculations suggest that their primary global polarizations fulfill $P_{Ω^-}\simeq 5/3P_{Ξ^-}\simeq 5/3P_Λ$. We also estimate the feed-down effect of particle decay on the global polarization. With the feed-down effect taken into account, the global polarizations of $Λ$ and $Ξ^-$ are clearly separated, and the final global polarizations are in the ordering: $P_{Ω^-}>P_{Ξ^-}>P_Λ$. Such a relation can be tested in experiments, which will provide us more information about the global polarization mechanism.

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arXiv2021

Utilization of Event Shape in Search of the Chiral Magnetic Effect in Heavy-ion Collisions

The search for the chiral magnetic effect (CME) has been a subject of great interest in the field of high-energy heavy-ion collision physics, and various observables have been proposed to probe the CME. Experimental observables are often contaminated with background contributions arising from collective motions (specifically elliptic flow) of the collision system. We present a method study of event-shape engineering (ESE) that projects the CME-sensitive $γ_{112}$ correlator and its variations ($γ_{132}$ and $γ_{123}$) to a class of events with minimal flow. We discuss the realization of the zero-flow mode, the sensitivity on the CME signal, and the corresponding statistical significance for Au+Au, Ru+Ru, and Zr+Zr collisions at $\sqrt{s_{\rm NN}} = 200$ GeV with a multiphase transport (AMPT) model, as well as a new event generator, Event-By-Event Anomalous-Viscous Fluid Dynamics (EBE-AVFD).

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arXiv2021

Global hyperon polarization and effects of decay feeddown

We study the global polarizations of $Λ$, $Ξ^-$, and $Ω^-$ hyperons in noncentral Au+Au collisions at $\sqrt{s_\mathrm{NN}}=$ 7.7-200 GeV. We highlight the importance of effect of decay feeddown to the measured global polarization. With the decay contributions taken into account, the global polarization ordering $P_{Ω^-} > P_{Ξ^-} > P_Λ$ can be naturally explained, which is consistent with the observation recently reported from the STAR experiment from Au+Au collisions at 200 GeV. We also extend our calculations to predict expectations from the RHIC-BES II data.

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arXiv2021

Local spin alignment of vector mesons in relativistic heavy-ion collisions

We investigate the spin alignment of vector mesons arising from locally polarized quarks and anti-quarks (local spin alignment) in heavy-ion collisions. We find that $ρ_{00}\neq 1/3$ does not necessarily signal the global polarization of quarks and anti-quarks along the orbital angular momentum of the system, but may also originate from their local spin polarization. Such local spin polarization could be induced by local vorticity arising from the anisotropic expansion of the fireball. We further propose experimental observables that can distinguish between the local and the global spin alignments. Measurements of these observables in heavy-ion collisions can probe the vorticity pattern and shed light on the puzzles of $ϕ$ and $K^{*0}$ spin alignments.

nucl-th↗

arXiv2020

Evidence of Coalescence Sum Rule in Elliptic Flow of Identified Particles in High-energy Heavy-ion Collisions

The major goal of high-energy heavy-ion collisions is to study the properties of the deconfined quark gluon plasma (QGP), such as partonic collectivity. The collective motion of constituent quarks can be derived from the anisotropic flow measurements of identified hadrons within the coalescence framework. Based on published results of elliptic flow ($v_2$), we shall test the coalescence sum rule using $K^{\pm}$, $p$, ${\bar p}$, $Λ$ and ${\bar Λ}$, and further extract $v_2$ values for produced $u$($d$, $\bar u$, $\bar d$), $s$ and $\bar s$ quarks, as well as transported $u(d)$ quarks in 10-40\% Au+Au collisions at $\sqrt{s_{\rm NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39 and 62.4 GeV. We also attempt to link the $v_2$ difference between $π^-$ and $π^+$ to the different numbers of $u$ and $d$ quarks in the initial gold ions, and to relate the $v_2$ measurements of multi-strange hadrons to the formation times of $ϕ$, $Ω^\pm$ and $Ξ^+$.

nucl-ex↗

arXiv2020

On the clustering properties of produced particles in high-energy $pp$ collisions

Minijets provide useful information on parton interactions in the low transverse-momentum (low-$p_T$) region. Because minijets produce clusters, we study the clustering properties of produced particles in high-energy $pp$ collisions as a first step to identify minijets. We develop an algorithm to find clusters by using the k-means clustering method, in conjunction with a k-number (cluster number) selection principle in the space of pseudorapidity and azimuthal angles. We test the clustering algorithm using events generated by PYTHIA 8.1, for $pp$ collision at $\sqrt{s}=200$ GeV. We find that clustering of low-$p_T$ hadrons occurs in high multiplicity events. However similar clustering properties are also present for particles produced randomly in a finite pseudorapidity and azimuthal angle space. To distinguish the dynamics from random generations of events, it is necessary to examine the correlation between particles and between clusters. We find that the correlations between clusters may provide a useful tool to distinguish the underlying dynamics of the reaction mechanism.

hep-ph↗

arXiv2019

Background evaluations for the chiral magnetic effect with normalized correlators using a multiphase transport model

The chiral magnetic effect (CME) induces an electric charge separation in a chiral medium along the magnetic field that is mostly produced by spectator protons in heavy-ion collisions. The experimental searches for the CME, based on the charge-dependent angular correlations ($γ$), however, have remained inconclusive, because the non-CME background contributions are not well understood. Experimentally, the $γ$ correlators have been measured with respect to the second-order ($Ψ_{2}$) and the third-order ($Ψ_{3}$) symmetry planes, defined as $γ_{112}$ and $γ_{123}$, respectively. The expectation was that with a proper normalization, $γ_{123}$ would provide a data-driven estimate for the background contributions in $γ_{112}$. In this work, we calculate different harmonics of the $γ$ correlators using a charge-conserving version of a multiphase transport (AMPT) model to examine the validity of the said assumption. We find that the pure-background AMPT simulations do not yield an equality in the normalized $γ_{112}$ and $γ_{123}$, quantified by $κ_{112}$ and $κ_{123}$, respectively. Furthermore, we test another correlator, $γ_{132}$, within AMPT, and discuss the relation between different $γ$ correlators.

hep-ph↗