Thermodynamics of partonic matter in relativistic heavy-ion collisions from a multiphase transport model

2023

EPJ Web Conf.

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At low to moderate collision energies where the parton formation time τF is not small compared to the nuclear crossing time, the finite nuclear thickness significantly affects the energy density ϵ(t) and net conserved-charge densities such as the net-baryon density nB(t) produced in heavy ion collisions. As a result, at low to moderate energies the trajectory in the QCD phase diagram is also affected by the finite nuclear thickness. Here, we first discuss our semi-analytical model and its results on ϵ(f), nR(t), nQ(t), and ns(t) in central Au+Au collisions. We then compare the T(t), μB(t), μQ(t), and μS(t) extracted with the ideal gas equation of state (EoS) with quantum statistics to those extracted with a lattice QCD-based EoS. We also compare the T-μB trajectories with the RHIC chemical freezeout data. Finally, we discuss the effect of transverse flow on the trajectories.

Section: Resultssupporting

confidence: 91%

Calculating QCD Phase Diagram Trajectories of Nuclear Collisions using a Semi-analytical Model

Mendenhall

2023

EPJ Web Conf.

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“…While the T max values are often similar at the same collision energy (except for very low energies), the µ max B value is significantly larger in the quantum ideal gas EOS. This feature is also seen in the trajectories calculated from the AMPT model [5] and can be understood in terms of the Pauli exclusion principle in the quantum EOS.…”

mentioning

confidence: 57%

“…For this purpose, it is important to calculate or estimate the collision trajectory in the QCD phase diagram in the T −µ B plane or the general T −µ B −µ Q −µ S four-dimensional space. So far, this is mostly done by analyzing the time evolution of given volume cells in dynamical models [4,5] such as transport models and hydrodynamical models, which usually takes a lot of effort. A trajectory can also be estimated by using a given equation of state with assumptions such as imposing a constant s/n B (entropy to net-baryon-density ratio) along the trajectory [6].…”

Section: Introductionmentioning

confidence: 99%

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A Semi-analytical Method of Calculating Nuclear Collision Trajectory in the QCD Phase Diagram

Mendenhall

2022

Supl. Rev. Mex. Fis.

The finite nuclear thickness affects the energy density (t) and conserved-charge densities such as the net-baryon density nB(t) produced in heavy ion collisions. While the effect is small at high collision energies where the Bjorken energy density formula for the initial state is valid, the effect is large at low collision energies, where the nuclear crossing time is not small compared to the parton formation time. The temperature T(t) and chemical potentials µ(t) of the dense matter can be extracted from the densities for a given equation of state (EOS). Therefore, including the nuclear thickness is essential for the determination of the T-µB trajectory in the QCD phase diagram for relativistic nuclear collisions at low to moderate energies such as the RHIC-BES energies. In this proceeding, we will first discuss our semi-analytical method that includes the nuclear thickness effect and its results on the densities є(t), nB(t), nQ(t), and nS(t). Then, we will show the extracted T(t), µB(t), µQ(t), and µS(t) for a quark-gluon plasma using the ideal gas EOS with quantum or Boltzmann statistics. Finally, we will show the results on the T-µB trajectories in relation to the possible location of the QCD critical end point. This semi-analytical model provides a convenient tool for exploring the trajectories of nuclear collisions in the QCD phase diagram.

“…In these previous studies, the QGP was simply considered to be an effective onecomponent system, specifically a gluon gas with added N f -flavor quark degrees of freedom [14,15,[18][19][20]. This is due to an oversaturated gluon density inside relativistic heavy ions before collision [18][19][20], forming a so-called "color glass condensate."…”

Section: Introductionmentioning

confidence: 99%

The shear viscosity of parton matter under anisotropic scatterings

MacKay

2022

Eur. Phys. J. C

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The shear viscosity $$\eta $$ η of a quark–gluon plasma in equilibrium can be calculated analytically using multiple methods or numerically using the Green–Kubo relation. It has been realized, which we confirm here, that the Chapman–Enskog method agrees well with the Green–Kubo result for both isotropic and anisotropic two-body scatterings. We then apply the Chapman–Enskog method to study the shear viscosity of the parton matter from a multi-phase transport model. In particular, we study the parton matter in the center cell of central and midcentral Au + Au collisions at 200A GeV and Pb + Pb collisions at 2760A GeV, which is assumed to be a plasma in thermal equilibrium but partial chemical equilibrium. As a result of using a constant Debye mass or cross section $$\sigma $$ σ for parton scatterings, the $$\eta /s$$ η / s ratio increases with time (as the effective temperature decreases), contrary to the trend preferred by Bayesian analysis of the experimental data or pQCD results that use temperature-dependent Debye masses. At $$\sigma =3$$ σ = 3 mb that enables the transport model to approximately reproduce the elliptic flow data of the bulk matter, the average $$\eta /s$$ η / s of the parton matter in partial equilibrium is found to be very small, between one to two times $$1/(4\pi )$$ 1 / ( 4 π ) .