We have attempted to describe the rapidity and transverse momentum spectra, simultaneously, of the hadrons produced in the Ultra-relativistic Nuclear Collisions. This we have tried to achieve in a single statistical thermal freeze-out model using single set of parameters. We assume the formation of a hadronic gas in thermo-chemical equilibrium at the freeze-out. The model incorporates a longitudinal as well as a transverse hydrodynamic flow. We have also found that the role of heavier hadronic resonance decay is important in explaining the particle spectra.

We attempt to describe the rapidity and transverse momentum spectra of strange as well as non-strange hadrons e.g.-and their ratios in the ultra-relativistic collisions of gold nuclei at √ s = 200 GeV. This is done by using a statistical thermal freeze-out model which incorporates the rapidity (collision) axis as well as transverse direction boosts developed within an expanding hot and dense hadronic fluid (fireball) till the final freeze-out. We determine the thermo-chemical freeze-out conditions particularly in terms of the temperature, baryon chemical potential and collective flow effect parameters for different particle species. The parameters indicate occurrence of freeze-out of the singly and doubly strange hyperon species at somewhat earlier times during the evolution of the fireball. The experimental data of the transverse momentum and rapidity distribution are well reproduced. The contribution of heavier hadronic resonance decay is taken into account.

The transverse momentum spectra of identified particles at midrapidity in Pb + Pb

Midrapidity results on multiplicity density [Formula: see text] and transverse momentum distributions [Formula: see text] of pions, kaons and protons in Au + Au collisions at [Formula: see text] are reproduced by using our earlier proposed Unified Statistical Thermal Freeze-out Model (USTFM). The calculated results are found to be in fairly good agreement with the experimental data points taken from STAR experiment. Freeze-out conditions in terms of a transverse flow velocity parameter and the thermal freeze-out temperature are extracted from the fits of transverse momentum spectra of the particles at different collision centralities. A large value of midrapidity chemical potential reveals the effects of almost complete stopping in the center-of-mass frame of the system produced. The resonance decay contributions are found to have a negligible effect on the transverse momentum spectra of the particles while these are found to be significant for determining the shape of the rapidity spectra.

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