Search

The new state of matter produced at Relativistic Heavy Ion Collider reveals a strongly coupled quark-gluon plasma with an extremely small shear viscosity to entropy density ratio eta/s. We calculate the eta/s of an equilibrated hadron matter characterized by a relativistic hadron resonance gas with a Hagedorn mass spectrum that grows exponentially with the hadron mass. We find with increase in temperature of the system the eta/s value decreases due to rapid increase in the multiplicity of massive resonances. In the vicinity of the critical temperature for deconfinement transition, the minimum value of eta/s in the Hagedorn resonance gas is found to be consistent with the current estimates for a strongly coupled quark-gluon plasma., Comment: 5 pages, RevTex, to appear in PLB

Within a relativistic mean-field model with nonlinear isoscalar–isovector coupling, we explore the possibility of constraining the density dependence of nuclear symmetry energy from a systematic study of the neutron skin thickness of finite nuclei and neutron star properties. We find the present skin data supports a rather stiff symmetry energy at subsaturation densities that corresponds to a soft symmetry energy at supranormal densities. Correlation between the skin of 208Pb and the neutron star masses and radii with kaon condensation has been studied. We find that 208Pb skin estimate suggest star radii that reveals considerable model dependence. Thus precise measurements of neutron star radii in conjunction with skin thickness of heavy nuclei could provide significant constraint on the density dependence of symmetry energy.

Using a multiphase transport model, we study the production of a new strange dibaryon (\Omega\Omega)_{0+} in dense hadronic matter formed in relativistic heavy ion collisions. The (multi-)strange baryons (\Xi and \Omega) are produced by strangeness-exchange reactions between antikaons and hyperons in the pure hadronic phase. The rescattering between the omegas at midrapidity leads to a production probability of \simeq 3x10^{-7} (\Omega\Omega)_{0+} per event at the RHIC energy of \sqrt s=130A GeV. The production probability would be enhanced by two orders of magnitude if (\Omega\Omega)_{0+} and omega reach chemical equilibrium during heavy ion collisions. We further find that the yield of (\Omega\Omega)_{0+} increases continuously from SPS to the highest RHIC energy., Comment: 4 pages, RevTex, 3 figs included

A relativistic transport model is used to study Xi- production in 2-11A GeV Au+Au collisions. Introducing the strangeness-exchange reactions between antikaons and hyperons as the sources for Xi-, we find that the cascade yield in these collisions is in reasonable agreement with the data. Although the Xi- abundance does not reach chemical equilibrium unless the cross section for strangeness-exchange reactions is enhanced by six times, it exhibits the strongest enhancement with increasing centrality of collision and with increasing beam energy., Comment: Title changed, Modified version, 5 pages, RevTex

Multifragmentation of toroidal and bubble nuclei envisaged to be formed in intermediate energy heavy ion collisions is studied in a statistical model with microcanonical simulation. Under given initial conditions, we calculate several observables that may possibly distinguish the exotic shapes from the spherical configuration.

Hadron production and their suppression in Pb + Pb collisions at LHC at a center-of-mass energy of s NN = 2.76 TeV are studied within a multiphase transport (AMPT) model whose initial conditions are obtained from the recently updated HIJING 2.0 model. The centrality dependence of charged hadron multiplicity d N ch / d η at midrapidity was found quite sensitive to the largely uncertain gluon shadowing parameter s g that determines the nuclear modification of the gluon distribution. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller gluon shadowing to be consistent with d N ch / d η data at LHC. With such a constrained parton shadowing, charged hadron and neutral pion production over a wide transverse momenta range are investigated in AMPT. Relative to nucleon–nucleon collisions, the particle yield in central heavy ion collisions is suppressed due to parton energy loss. While the calculated magnitude and pattern of suppression is found consistent with that measured in Au + Au collisions at s NN = 0.2 TeV at RHIC, at the LHC energy the suppression is overpredicted which may imply the medium formed at LHC is less opaque than expected from simple RHIC extrapolations. Reduction of the QCD coupling constant α s by ∼ 30 % in the higher temperature plasma formed at LHC as compared to that at RHIC was found to reproduce the measured suppression at LHC.

Starting with the relativistic Boltzmann equation where the collision term is generalized to include nonlocal effects via gradients of the phase-space distribution function, and using Grad's 14-moment approximation for the distribution function, we derive equations for the relativistic dissipative fluid dynamics. We compare them with the corresponding equations obtained in the standard Israel-Stewart and related approaches. Our method generates all the second-order terms that are allowed by symmetry, some of which have been missed by the traditional approaches based on the 14-moment approximation, and the coefficients of other terms are altered. The first-order or Navier-Stokes equations too get modified. Significance of these findings is demonstrated in the framework of one-dimensional scaling expansion of the matter formed in relativistic heavy-ion collisions., Comment: 5 pages, 3 figures, version to appear in PLB