Centrality dependence of pseudo-rapidity distribution in nucleus–nucleus collisions at (4.1–4.5) AGeV/c

A detailed study of the centrality dependence of pseudo-rapidity distribution has been carried out for [Formula: see text]O-emulsion interactions at 4.5[Formula: see text]AGeV/c and [Formula: see text]Ne-emulsion interactions at 4.1[Formula: see text]AGeV/c using nuclear emulsion track detector. Depending on the values of the total charges or sum of the charges of noninteracting projectile fragments, event samples were classified into four centrality classes. Maximum pseudo-rapidity density, average pseudo-rapidity values, moments of pseudo-rapidity distribution along with skewness and kurtosis of the distributions have been investigated for different centrality classes.

Adiabatic expansion of nuclear matter gas to describe violation of Feynman scaling law in multiple particle production

The main features of the rapidity density distribution of the produced hadrons in multiple particle production in nucleon collisions are; (a) the distribution in the forward region (ȳ ≥ 0) has a shape similar to the Fermi distribution, (b) the distribution in the most forward region reaches almost the maximum rapidity ymax = ln(√s/M) (M : nucleon mass), and (c) the shrinkage of the distribution from the maximum rapidity increases with the incident energy (i.e. violation of Feynman scaling law). These features are possible to be described by the assumptions that; (1) a fireball of the gas (made of nuclear matter, with the temperature Ti and with the shape of the incident nucleon with Lorentz contraction) is produced in the collision, (2) the fireball makes the adiabatic expansion, and (3) the constituent particles of the gas obey the Maxwell-Boltzmann distribution of the temperature Tf in the final state.

New Exact Solutions of Relativistic Hydrodynamics for Longitudinally Expanding Fireballs

We present new, exact, finite solutions of relativistic hydrodynamics for longitudinally expanding fireballs for arbitrary constant value of the speed of sound. These new solutions generalize earlier, longitudinally finite, exact solutions, from an unrealistic to a reasonable equation of state, characterized by a temperature independent (average) value of the speed of sound. Observables such as the rapidity density and the pseudorapidity density are evaluated analytically, resulting in simple and easy to fit formulae that can be matched to the high energy proton–proton and heavy ion collision data at RHIC and LHC. In the longitudinally boost-invariant limit, these new solutions approach the Hwa–Bjorken solution and the corresponding rapidity distributions approach a rapidity plateaux.

DESCRIPTION OF (PSEUDO-)RAPIDITY DENSITY AND TRANSVERSE MOMENTUM DISTRIBUTIONS IN A WIDE ENERGY RANGE $(\sqrt{s} = 22.4\hbox{--}7000~{\rm GeV})$

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 [Formula: see text], due to lack of experimental data at the most-forward rapidity region. The pseudo-rapidity density distribution at LHC energy [Formula: see text] expected by the present formulation is compared with those by the other models.