Particle Ratios in Heavy-Ion Collisions

Abstract

In framework of statistical models, different particle ratios at energies ranging from $3.5$ to $200$GeV are calculated. Assuming that the particle production takes place along the freeze-out curve, we study the sharp peak in $K^{+}/{\pi }^{+}$ ratio observed at SPS energy. We study the responsibility of non-equilibrium quark occupancy of phase space ${\gamma }_i$ for particle production. Allowing ${\gamma }_i$ to take values other than that of equilibrium, we got a very well description for $K^{+}/{\pi }^{+}$ ratio at all energies. Using the resulting parameter set, we analyzed the $K^{-}/{\pi }^{-}$, $\Lambda /{\pi }^{+}$ and \hbox{$\Lambda /<\pi >$} ratios. We found that the corresponding peaks all are located at the same value of energy, ${\sqrt{s_{NN}}}^{(c)}\simeq 7.5$GeV. At this energy, the entropy per particle is singular. The saddle-point in entropy per particle likely refers to critical phenomenon and change in the phase space.

Comments: 10 pages, 5 figures and 1 table to be appear in Prog. Theor. Phys