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 PT and centrality in top 8.5% central region. Little centrality dependence of the K-/K+ and p/p ratios is observed. The transverse mass mT distribution and dN/dy of K+, K-, p and p around mid-rapidity are obtained. The temperature Tch and the chemical potentials for both light and strange quarks (μq, μs) at chemical freeze-out are determined by applying a simple thermodynamical model to the present data. The resultant μq, μs and Tch are compared with those obtained from similar analysis of SPS S+A and AGS Si+A data. The chemical freeze-out temperature Tch at CERN energies is higher than thermal freeze-out temperature Tfo which is extracted from mT distribution of charged hadrons. At AGS energies Tch is close to Tfo. (orig.)