Production of Resonances in Partial Chemical Equilibrium

Abstract

Within the model of partial chemical equilibrium (PCE) we calculate the multiplicity ratios of selected unstable resonances to given stable species. We focus on those ratios that have been measured either in Pb+Pb collisions at the LHC or in Au+Au collisions at the top RHIC energy. The model provides an interpretation how in an expanding hadronic fireball with decreasing temperature the final numbers of stable hadrons after decays of all resonances remain unchanged. Each stable species acquires its own chemical potential and the resonances are kept in equilibrium with them. Multiplicities of unstable resonances provide a test of this scenario. We observe that the ratios of $K^{*}/K$ and $\rho^0/\pi$ fit reasonably well into the picture of single kinetic freeze-out of the single-particle spectra, but the $\phi$-meson and hyperon resonances are not reproduced by this model.