Kaon and proton ratios from central Pb+Pb collisions at the CERN SPS

K −/K + and p ¯ / p ratios measured in 158 A·GeV Pb+Pb collisions are shown as a function of transverse momentum P T and centrality in top 8.5% central region. Little centrality dependence of the K −/ K + and p ¯ / p ratios is observed. The transverse mass m T distribution and dN/dy of K +, K −, p and p ¯ around mid-rapidity are obtained. The temperature T ch and the chemical potentials for both light and strange quarks (μ q, μ s) at chemical freeze-out are determined by applying simple thermodynamical model to the present data. The resultant μ q, μ s and T ch are compared with those obtained from similar analysis of SPS S+A and AGS Si+A data. The chemical freeze-out temperature T ch at CERN energies is higher than thermal freeze-out temperature T fo which is extracted from m T distribution of charged hadrons. At AGS energies T ch is close to T fo .