A new equation of state for a hot and dense hadron gas (HG) is obtained where the finite hard-core size of baryons has been incorporated in a thermodynamically consistent formulation of excluded volume correction. Our model differs from other existing approaches on the following points. We assign a hard-core volume only to each baryon and mesons though possess a small volume but they can fuse and interpenetrate into one another. Use of the full quantum statistics is made in obtaining the grand canonical partition function where excluded-volume correction has been incorporated by explicitly integrating over volume. We thus find that the new model works even for the cases of extreme temperatures and/or densities where most of other approaches fail.The model does not violate causality even at extreme densities. The temperature and density dependence of various thermodynamical quantities, e.g. pressure, baryon density, entropy and energy density compare well with the results of other microscopic HG models. After suitable parametrization of the centre-of-mass energy in terms of temperature and baryon chemical potential, we explore some new freeze-out criteria which exhibit full independence of the collision energy and of the structures of the colliding nuclei. We further demonstrate the suitability of our model in explaining various experimental results of the multiplicity-ratios of various particles and their antiparticles. Finally, we use our excluded-volume model to obtain the transport behaviour of the hot and/or dense HG such as shear viscosity to entropy ratio, speed of sound etc. and compare the results with earlier calculations.
Recent theoretical investigations have unveiled a rich structure in the quantum chromodynamics (QCD) phase diagram which consists of quark gluon plasma (QGP) and the hadronic phases but also supports the existence of a cross-over transition ending at a critical end point (CEP). We find a too large variation in determination of the coordinates of the CEP in the temperature (T), baryon chemical potential (µ B ) plane and, therefore, its identification in the current heavy-ion experiments becomes debatable. Here we use an equation of state (EOS) for a deconfined QGP using a thermodynamically consistent quasiparticle model involving quarks and gluons having thermal masses. We further use a thermodynamically consistent excluded volume model for the hadron gas (HG) which was recently proposed by us. Using these equations of state, a first order deconfining phase transition is constructed using Gibbs' criteria. This leads to an interesting finding that the phase transition line ends at a critical point (CEP) beyond which a cross-over region exists. Using our thermal HG model, we obtain a chemical freeze out curve and we find that the CEP lies in close proximity to this curve as proposed by some authors. The coordinates of CEP are found to lie within the reach of RHIC experiment.
We analyse the transverse momentum (pT)-spectra as a function of charged-particle multiplicity at midrapidity (|y| < 0.5) for various identified particles such as π ± , K ± , K 0 S , p + p, φ, K * 0 + K * 0 , and Λ +Λ in proton-proton collisions at √ s = 7 TeV using Boltzmann-Gibbs Blast Wave (BGBW) model and thermodynamically consistent Tsallis distribution function. We obtain the multiplicity dependent kinetic freeze-out temperature (T kin ) and radial flow (β) of various particles after fitting the pT-distribution with BGBW model. Here, T kin exhibits mild dependence on multiplicity class while β shows almost independent behaviour. The information regarding Tsallis temperature and the non-extensivity parameter (q) are drawn by fitting the pT-spectra with Tsallis distribution function. The extracted parameters of these particles are studied as a function of charged particle multiplicity density (dN ch /dη). In addition to this, we also study these parameters as a function of particle mass to observe any possible mass ordering. All the identified hadrons show a mass ordering in temperature, non-extensive parameter and also a strong dependence on multiplicity classes, except the lighter particles. It is observed that as the particle multiplicity increases, the q-parameter approaches to Boltzmann-Gibbs value, hence a conclusion can be drawn that system tends to thermal equilibrium. The observations are consistent with a differential freeze-out scenario of the produced particles.
Location of critical point and mapping the QCD phase boundary still exists as one of the most interesting and studied problems of heavy-ion physics. A new equation of state(EOS) for a gas of extended baryons and pointlike mesons is presented here which accounts for the repulsive hardcore interactions arising due to the geometrical size of the baryons. A first order deconfining phase transition is obtained using Gibbs' equilibrium criteria and a bag model EOS for the weakly interacting quark matter. It is interesting to find that the phase transition line ends at a critical point beyond which a cross-over region exists between hot-dense meson gas and quark-antiquark gluon matter. Our curve resembles in shape closely with the predicitions of the available lattice gauge calculations and also reproduces the conjectured phase boundary.
We take the experimental data for transverse momentum spectra of identified charged hadrons in different centrality classes for nucleus-nucleus (A+A) collisions at various Relativistic Heavy-Ion Collider (RHIC) energies measured by the STAR collaboration. We analyse these data in the framework of color string percolation model (CSPM) in order to extract various percolation parameters at different centralities at RHIC energies to study the effect of collision geometry and collision energy. We use these parameters to study the centrality dependent behaviour of initial temperature of the percolation cluster, energy density, average transverse momentum, shear viscosity to entropy density ratio (η/s) and trace anomaly for different energies at RHIC from √ sNN = 19.6 to 200 GeV. These observables are found to strongly depend on centrality at various collision energies. The critical percolation density, which is related to the deconfinement phase transition is achieved in the most central nucleus-nucleus collisions, while it fails in the peripheral collisions. A universal scaling is observed in color suppression factor and initial temperatures when studied as a function of charged particle pseudorapidity distribution scaled by nuclear overlap area at RHIC energies. The minimum of η/s is observed in the most central collisions at √ sNN = 130 and 200 GeV.PACS numbers: 25.75.Gz,25.75.Nq,12.38.Mh * Corresponding Author Email: Raghunath.Sahoo@cern.ch average transverse momentum, shear viscosity to entropy density ratio, and trace anomaly at RHIC energies. The paper runs as follows. First, we present the formulation and methodology in section II. In section III, we present the results and discussions. Finally, the findings of this work are summarized in section IV.
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