We discuss how the inclusion of Hagedorn states near $T_c$ leads to short chemical equilibration times of proton anti-proton pairs, $K\bar{K}$ pairs, and $Λ\barΛ$ pairs, which indicates that hadrons do not need to be "born" into chemical equilibrium in ultrarelativistic heavy ion collisions. We show that the hadron ratios computed within our model match the experimental results at RHIC very well. Furthermore, estimates for $η/s$ near $T_c$ computed within our resonance gas model are comparable to the string theory viscosity bound $η/s=1/4π$. Our model provides a good description of the recent lattice results for the trace anomaly close to $T_c=196$ MeV.
We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma using the first principles method of QCD effective kinetic theory, accurate at weak coupling. In longitudinally expanding systems--relevant for relativistic nuclear collisions--we find that for realistic couplings chemical equilibration takes place after hydrodynamization, but well before local thermalization. We estimate that hadronic collisions with final state multiplicities ${dN_\text{ch}}/{dη}\gtrsim 10^2$ live long enough to reach approximate chemical equilibrium, which is consistent with the saturation of strangene…
We performed state-of-the-art QCD effective kinetic theory simulations of chemically equilibrating QGP in longitudinally expanding systems. We find that chemical equilibration takes place after hydrodynamization, but well before local thermalization. By relating the transport properties of QGP and the system size we estimate that hadronic collisions with final state multiplicities $dN_\text{ch}/dη> 10^2$ live long enough to reach approximate chemical equilibrium for all collision systems. Therefore we expect the saturation of strangeness enhancement to occur at the same multiplicity in proton-…
I argue that perturbative scattering of quarks and gluons are incompatible with lattice and heavy ion data on QGP properties. The non-perturbative mechanisms for quasiparticle rescattering and quark production are briefly discussed, as well as experiments needed to measure matter anisotropy and quark density at early stages of the collisions.
We study thermalization, hydrodynamization, and chemical equilibration in out-of-equilibrium Quark-Gluon Plasma starting from various initial conditions using QCD effective kinetic theory, valid at weak coupling. In non-expanding systems gauge bosons rapidly lose information of the initial state and achieve kinetic equilibrium among themselves, while fermions approach the equilibrium distribution only at later time. In systems undergoing rapid longitudinal expansion, both gluons and quarks are kept away from equilibrium by the expansion, but the evolution is well described by fluid dynamics ev…
We solve a leading-order QCD kinetic theory with light quarks and gluon degrees of freedom to study the non-equilibrium dynamics of the quark-gluon plasma (QGP). By including both elastic and inelastic scatterings for quarks and gluon, the model is proficient to describe kinetic and chemical equilibration of the QGP, and thus connects the initial (semi-) hard production of partons at early times with the hydrodynamic description of a near-thermalized quark-gluon plasma after the first fm/c of the collision. Within this approach, we investigate the time scales and mechanisms for kinetic and che…
We have estimated centrality variation of chemical freeze-out parameters from yield data at mid-rapidity of $π^\pm$, $K^\pm$ and $p$, $\bar{p}$ for collision energies of RHIC (Relativistic Heavy Ion Collider), Beam Energy Scan (RHIC-BES) program, and LHC (Large Hadron Collider). We have considered a simple hadron resonance gas model and employed a formalism involving conserved charges ($B, Q, S$) of QCD for parameterization. Along with temperature and three chemical potentials ($T,μ_B,μ_Q,μ_S$), a strangeness under-saturation factor ($γ_S$) has been used to incorporate the partial equilibratio…
We employ a non-equilibrium Quantum Chromodynamics (QCD) kinetic description to study the kinetic and chemical equilibration of the Quark-Gluon Plasma (QGP) at weak coupling. Based on our numerical framework, which explicitly includes all leading order processes involving light flavor degrees of freedom, we investigate the thermalization process of homogeneous and isotropic plasmas far-from equilibrium and determine the relevant time scales for kinetic and chemical equilibration. We further simulate the longitudinally expanding pre-equilibrium plasma created in ultrarelativistic heavy-ion coll…
We investigate the medium induced fragmentation of jets in a high-temperature QCD plasma. Based on an effective kinetic theory of QCD, we study the non-equilibrium evolution of the jet shower and the chemical equilibration of jet fragments in the medium. By including radiative emissions as well as elastic interactions, our approach extends all the way from the jet energy scale to the temperature of the medium and includes important effects such as the recoil of the medium. We present results for the in-medium fragmentation, including chemical and kinetic equilibration of the soft fragments and…
We investigate the density fluctuations induced by hadronic interactions at low temperatures and large chemical potentials after the hadronization of quark-gluon plasma~(QGP). We analyze the structures of net-baryon number kurtosis and skewness and elaborate on their relations with the nuclear liquid-gas~(LG) phase transition and hadronic interactions above the critical temperature. Combining with the relevant experimental projects at RHIC/NICA/FAIR/J-PARC/HIAF with collision energies from $200\,$GeV to $1.8\,$GeV, we propose a double-peak structure of kurtosis (skewness) as a function of coll…
Heavy baryonic resonances, multistrange hadrons, and equilibration at energies available at the GSI Schwerionensynchrotron, SIS18
利用UrQMD输运模型研究了靶束能量为$E_{\mathrm{lab}}= 1.76$ A GeV的核碰撞中粒子产生的细节和时间依赖性。我们发现，以前提出的多奇异强子产生机制$ϕ$和$Ξ$是可能的，这是由于入射核与已经产生的核共振的次级相互作用，而核的费米动量只起次要作用.我们还展示了这些粒子多重性的中心依赖性如何被用来确认所提出的机制，因为它强烈依赖于反应中参与者的数量。此外，我们调查的时间依赖性的粒子生产在碰撞中的Ca+Ca在这个光束的能量，为了了解测量的粒子产量的表观化学平衡的起源。我们发现，确实轻强子产额似乎已经在平衡从碰撞的早期阶段，而事实上没有本地平衡，通过多碰撞过程，发生。表观平衡仅通过根据可用相空间的共振衰减来达到。
A Calculation of Baryon Diffusion Constant in Hot and Dense Hadronic Matter Based on an Event Generator URASiMA
利用事件发生器URASiMA（Ultra-Relativistic AA Collision Simulator based on Multiple Scattering Algorithm）计算了稠密热强子物质的物理量和输运系数。在能量密度和重子数密度守恒的条件下，通过对URASiMA的模拟施加周期性边界条件，生成了具有固定温度和化学势的平衡态统计系综.分别通过能量分布中斜率参数的共同值和所含粒子数的饱和度来确定热平衡和化学平衡的实现。利用所产生的系综，我们研究了稠密热强子物质的重子扩散常数对温度和化学势的依赖关系。
