Kaon spectra from p+Be to Pb+Pb collisions

Abstract

The yields and inverse slopes ofK ^± M_T distributions at central rapidity are presented for pBe, pS, pPb, SS, SPb and PbPb collisions. The ratios ofK ⁻/K⁺ and${{\bar p} \mathord{\left/ {\vphantom {{\bar p} p}} \right. \kern-\nulldelimiterspace} p}$ decrease with system size and centrality. Comparing the slopes of pions, kaons and protons suggests that transverse flow is present in AA collisions but not in pPb collisions. For PbPb collisions the inverse slopes of theK ⁻ andK ⁺ M_T spectra are very close but for pPb the inverse slope ofK ⁺ exceeds that ofK ⁻. These results suggest that thermal equilibrium is reached in central heavy ion collisions but not in pPb collisions.