An expanding spherical fireball model for light hadron production at RHIC ($\sqrt{s_{\rm NN}}=7.7$--$39$ GeV)

Abstract

We investigate the transverse momentum ($p_T$) spectra and rapidity distributions of the light hadrons $π^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ produced in Au+Au collisions at RHIC for $\sqrt{s_{\rm NN}} = 7.7$--39 GeV and different collision centralities. The produced medium is modeled as an expanding spherical fireball, with the radial expansion velocity determined from the rate of increase of the fireball radius. The particle spectra are calculated using the Cooper--Frye freeze-out prescription with a local equilibrium distribution function and a blast-wave-like flow profile. The model parameters are fixed from the midrapidity $p_T$ spectra of pions at kinetic freeze-out for different centralities. The same parameters are then used for the other hadron species, with the kinetic freeze-out chemical potential as the only additional free parameter. The model provides a good description of the STAR collaboration data for the $p_{T}$ spectra of light hadrons and predicts Gaussian-like rapidity distributions over the considered energy range across different centralities.