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تسجيل مستخدم جديدBulk Properties of the Medium Produced in Relativistic Heavy-Ion Collisions from the Beam Energy Scan Program
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We present measurements of bulk properties of the matter produced in Au+Au collisions at $sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, and 39 GeV using identified hadrons ($pi^pm$, $K^pm$, $p$ and $bar{p}$) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity ($|y|<$0.1) results for multiplicity densities $dN/dy$, average transverse momenta $langle p_T rangle$ and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic measurements of bulk properties of matter formed in heavy-ion collisions over a broad range of energy (or baryon chemical potential) at RHIC.
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The baryon and energy densities attained in fragmentation regions in central Au+Au collisions in the energy range of the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) are estimated within the model of the three-fluid dy
namics. It is shown that a considerable part of the baryon charge is stopped in the central fireball. Even at 39 GeV, approximately 70% of the total baryon charge turns out to be stopped. The fraction of this stopped baryon charge decreases with collision energy rise, from 100% at 7.7 GeV to $sim$40% at 62 GeV. The highest initial baryon densities of the thermalized matter, $n_B/n_0 approx$ 10, are reached in the central region of colliding nuclei at $sqrt{s_{NN}}=$ 20--40 GeV. These highest densities develop up to quite moderate freeze-out baryon densities at the midrapidity because the matter of the central fireball is pushed out to fragmentation regions by one-dimensional expansion. Therefore, consequences of these high initial baryon densities can be observed only in the fragmentation regions of colliding nuclei in AFTER@LHC experiments in the fixed-target mode.
Results from the Beam Energy Scan (BES) program conducted recently by STAR experiment at RHIC are presented. The data from Phase-I of the BES program collected in Au+Au collisions at center-of-mass energies (sqrt{s_{NN}}) of 7.7, 11.5, 19.6, 27, and
39 GeV cover a wide range of baryon chemical potential ?mu_B (100-400 MeV) in the QCD phase diagram. Several STAR results from the BES Phase-I related to turn-off of strongly inter- acting quark-gluon plasma (sQGP) signatures and signals of QCD phase boundary are reported. In addition to this, an outlook is presented for the future BES Phase-II program and a possible fixed target program at STAR.
Results from the Beam Energy Scan (BES) program conducted by STAR experiment at RHIC are presented. The data from Phase-I of the BES program collected in Au+Au collisions at center-of-mass energies ($sqrt{s_{NN}}$) of 7.7, 11.5, 19.6, 27, and 39 GeV
cover a wide range of baryon chemical potential $mu_{B}$ (100--400 MeV) in the QCD phase diagram. Several STAR results from the BES Phase-I related to turn-off of strongly interacting quark--gluon plasma (sQGP) signatures and signals of QCD phase boundary are reported. In addition to this, an outlook is presented for the future BES Phase-II program and a possible fixed target program at STAR.
In this paper, we investigate the kinetic freeze-out properties in relativistic heavy ion collisions at different collision energies. We present a study of standard Boltzmann-Gibbs Blast-Wave (BGBW) fits and Tsallis Blast-Wave (TBW) fits performed on
the transverse momentum spectra of identified hadrons produced in Au + Au collisions at collision energies of $sqrt{s_{rm{NN}}}=$ 7.7 - 200 GeV at the Relativistic Heavy Ion Collider (RHIC), and in Pb + Pb collisions at collision energies of $sqrt{s_{rm{NN}}}=$ 2.76 and 5.02 TeV at the Large Hadron Collider (LHC). The behavior of strange and multi-strange particles is also investigated. We found that the TBW model describes data better than the BGBW one overall, and the contrast is more prominent as the collision energy increases as the degree of non-equilibrium of the produced system is found to increase. From TBW fits, the kinetic freeze-out temperature at the same centrality shows a weak dependence of collision energy between 7.7 and 39 GeV, while it decreases as collision energy continues to increase up to 5.02 TeV. The radial flow is found to be consistent with zero in peripheral collisions at RHIC energies but sizable at LHC energies and central collisions at all RHIC energies. We also observed that the strange hadrons, with higher temperature and similar radial flow, approach equilibrium more quickly from peripheral to central collisions than light hadrons. The dependence of temperature and flow velocity on non-equilibrium parameter ($q-1$) is characterized by two second-order polynomials. Both $a$ and $dxi$ from the polynomials fit, related to the influence of the system bulk viscosity, increase toward lower RHIC energies.
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nature of deconfinement phase transition. There has been much speculation that the non-monotonic behavior of $kappasigma^{2}$ of the produced protons around $sqrt{s_{rm NN}}$ = 19.6 GeV in the STAR results may be due to the existence of QCD critical point. However, the experimentally measured proton distributions contain protons from heavy resonance decays, from baryon stopping and from direct production processes. These proton distributions are used to estimate the net-proton number fluctuation. Because it is difficult to disentangle the protons from the above-mentioned sources, it is better to devise a method which will account for the directly produced baryons (protons) to study the dynamical fluctuation at different center-of-mass energies. This is because, it is assumed that any associated criticality in the system could affect the particle production mechanism and hence the dynamical fluctuation in various conserved numbers. In the present work, we demonstrate a method to estimate the number of stopped protons at RHIC BES energies for central $0-5%$ auau collisions within STAR acceptance and discuss its implications on the net-proton fluctuation results.
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