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

   https://doi.org/10.31349/SuplRevMexFis.3.040920  

   Lin, Zi-Wei; Mendenhall, Todd (December 2022, Suplemento de la Revista Mexicana de Física)

   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. 

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2. 4D-TExS: A new 4D lattice-QCD equation of state with extended density coverage

   https://doi.org/10.1051/epjconf/202531606002  

   Jahan, Johannes; Abuali, Ahmed; Borsányi, Szabolcs; Kahangirwe, Micheal; Parotto, Paolo; Pásztor, Attila; Ratti, Claudia; Shah, Hitansh; Trabulsi, Seth A (January 2025, EPJ Web of Conferences)

   Cheshkov, C; Guernane, R; Maire, A (Ed.)

   Although calculations of QCD thermodynamics from first-principle lattice simulations are limited to zero net-density due to the fermion sign problem, several methods have been developed to extend the equation of state (EoS) to finite values of theB,Q,Schemical potentials. Taylor expansion aroundµ_i=0 (i = B,Q,S) enables to cover with confidence the region up toµ_i/T< 2.5. Recently, a new method has been developed to compute a 2D EoS in the (T,µ_B) plane. It was constructed through aT-expansion scheme (TExS), based on a resummation of the Taylor expansion, and is trusted up to densities aroundµ_B/T= 3.5. We present here the new 4D-TExS EoS, a generalization of the TExS to all 3 chemical potentials, expected to offer a larger coverage than the 4D Taylor expansion EoS. After explaining the basics of theT-Expansion Scheme and how it is generalized to multiple dimensions, we will present results for thermodynamic observables as functions of temperature and both finite baryon and strangeness chemical potentials. 

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3. New proxies for second-order cumulants of conserved charges in heavy-ion collisions within the EPOS4 framework

   https://doi.org/10.1103/PhysRevC.110.035201  

   Jahan, Johannes; Ratti, Claudia; Stefaniak, Maria; Werner, Klaus (September 2024, Physical Review C)

   Proxies for cumulants of baryon number $B$, electric charge $Q$, and strangeness $S$are usually measured in heavy-ion collisions via moments of net-number distribution of given hadronic species. Since these cumulants of conserved charges are expected to be sensitive to the existence of a critical point in the phase diagram of nuclear matter, it is crucial to ensure that the proxies used as substitutes are as close to them as possible. Hence, we use the 4 framework to generate $\text{Au}+\text{Au}$collisions at several collision energies of the BNL Relativistic Heavy Ion Collider beam energy scan. We compute second-order net cumulants of $\pi$, $K$, and $p$, for which experimental data have been published as well as the corresponding conserved charge cumulants. We then compare them with proxies, defined in previous lattice QCD and hadron resonance gas model studies, which are shown to reproduce more accurately their associated conserved charge cumulants. We investigate the impact of hadronic rescatterings occurring in the late evolution of the system on these quantities, as well as the amount of signal actually originating from the bulk medium which endures a phase transition. 

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4. Shear viscosity at finite baryon densities

   https://doi.org/10.1051/epjconf/202225913006  

   McLaughlin, E; Rose, J; Dore, T; Parotto, P; Ratti, C; Noronha-Hostler, J (January 2022, EPJ Web of Conferences)

   David, G.; Garg, P.; Kalweit, A.; Mukherjee, S.; Ullrich, T.; Xu, Z.; Yoo, I.-K. (Ed.)

   We use the excluded volume Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate η T/w at low temperatures and at finite baryon densities ρ B . This η T/w is then matched to a QCD-based shear viscosity calculation of the QGP for different profiles of η T/w across T,μ B including cross-over and critical point transitions. When compared to ideal hydrodynamic trajectories across T,μ B , we find that the η T/w (T,μ B ) profiles would require initial conditions at much larger baryon density to reach the same freeze-out point. 

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5. QCD equation of state at finite chemical potentials for relativistic nuclear collisions

   https://doi.org/10.1142/S0217751X21300076  

   Monnai, Akihiko; Schenke, Björn; Shen, Chun (March 2021, International Journal of Modern Physics A)

   null (Ed.)

   We review the equation of state of QCD matter at finite densities. We discuss the construction of the equation of state with net baryon number, electric charge, and strangeness using the results of lattice QCD simulations and hadron resonance gas models. Its application to the hydrodynamic analyses of relativistic nuclear collisions suggests that the interplay of multiple conserved charges is important in the quantitative understanding of the dense nuclear matter created at lower beam energies. Several different models of the QCD equation of state are discussed for comparison. 

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