Narrow Results

The distribution of nucleons participating in elliptical flow is studied for the reactions of ${}_{79}^{197}\mathrm{\text{Au}}+{}_{79}^{197}\mathrm{\text{Au}}$, ${}_{60}^{150}\mathrm{\text{Nd}}+{}_{60}^{150}\mathrm{\text{Nd}}$, ${}_{50}^{124}\mathrm{\text{Sn}}+{}_{50}^{124}\mathrm{\text{Sn}}$, ${}_{44}^{96}\mathrm{\text{Ru}}+{}_{44}^{96}\mathrm{\text{Ru}}$, ${}_{36}^{78}\mathrm{\text{Kr}}+{}_{36}^{78}\mathrm{\text{Kr}}$, ${}_{20}^{48}\mathrm{\text{Ca}}+{}_{20}^{48}\mathrm{\text{Ca}}$ and ${}_{20}^{40}\mathrm{\text{Ca}}+{}_{20}^{40}\mathrm{\text{Ca}}$ using isospin-dependent quantum molecular dynamics (IQMD) model for various centrality ranges and over the wide range of intermediate energy. Our findings reveal that the sigma (width) of rapidity distribution obtained varies with mass of colliding system at a given energy. The peak of rapidity distribution decreases with decrease in the mass of colliding nuclei. Transition energy as well as width of rapidity distribution depends on the mass of fragment for a given centrality. Influence of isospin dependent symmetry energy and nucleon–nucleon cross-section can be studied using rapidity distribution. Second transition energy depends on the mass of the fragment. Rotational phenomenon of nucleons can be observed for nucleons participating in elliptical flow.

We consider a possible mechanism of thermalization of nucleons in relativistic heavy-ion collisions. Our model belongs, to a certain degree, to the transport ones; we investigate the evolution of the system created in nucleus–nucleus collision, but we parametrize this development by the number of collisions of every particle during evolution rather than by the time variable. We based on the assumption that the nucleon momentum transfer after several nucleon–nucleon (–hadron) elastic and inelastic collisions becomes a random quantity driven by a proper distribution. This randomization results in a smearing of the nucleon momenta about their initial values and, as a consequence, in their partial isotropization and thermalization. The trial evaluation is made in the framework of a toy model. We show that the proposed scheme can be used for extraction of the physical information from experimental data on nucleon rapidity distribution.

Net proton rapidity distributions are calculated, reproduce very well data obtained at AGS, SPS, RHIC and predict results for the LHC experiment.¹ Presence of non-ideal plasma effects due to strongly coupled plasma in the early stage of relativistic heavy-ion collisions is investigated in the framework of non-conventional statistical mechanics.

The rapidity density and transverse momentum distributions of produced particles in multiple particle production are formulated assuming that the produced particles are emitted isotropically from several emitting centers. The energy distribution of produced particles in the rest frames of respective emitting centers is that of the Tsallis statistics. The distribution of emitting centers is flat with slanting cuts at both shoulders on the rapidity axis in the center of mass system. The formulation includes six adjustable parameters, among which four are energy dependent and more important and are determined so that the transverse momentum and the (pseudo-)rapidity density distributions fit to the data at various energies. The energy dependences of the four parameters, determined empirically, reproduce quite well the energy dependence of the average transverse momentum, that of the pseudo-rapidity density at η* = 0 and that of the charged multiplicity. The energy dependence of the inelasticity is either increasing or decreasing from the assumed value of K = 0.5 at , due to lack of experimental data at the most-forward rapidity region. The pseudo-rapidity density distribution at LHC energy expected by the present formulation is compared with those by the other models.

We discuss a recently found family of exact and analytic, finite and accelerating, $(1+1)$-dimensional solutions of perfect fluid relativistic hydrodynamics to describe the pseudorapidity densities and longitudinal HBT-radii and to estimate the lifetime parameter and the initial energy density of the expanding fireball in Au+Au collisions at RHIC with $\sqrt{s_{NN}}=130$ GeV and 200 GeV colliding energies. From these exact solutions of relativistic hydrodynamics, we derive a simple and powerful formula to describe the pseudorapidity density distributions in high-energy proton–proton and heavy-ion collisions, and derive the scaling of the longitudinal HBT radius parameter as a function of the pseudorapidity density. We improve upon several oversimplifications in Bjorken’s famous initial energy density estimate, and apply our results to estimate the initial energy densities of high-energy reactions with data-driven pseudorapidity distributions. When compared to similar estimates at the LHC energies, our results indicate a surprising and nonmonotonic dependence of the initial energy density on the energy of heavy-ion collisions.

The rapidity distributions of $J/\psi$ mesons produced in proton-lead ($p$-Pb) collisions at center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=5$TeV are studied by using a multisource thermal model and compared with the experimental data of the LHCb and ALICE Collaborations. Correspondingly, the pseudorapidity distributions are accurately obtained from the parameters extracted from the rapidity distributions. At the same time, the transverse momentum distributions in the same experiments are described by the simplest Erlang distribution which is the folding result of two exponential distributions which are contributed by the target and projectile partons, respectively.