K(892)⁰ and K(892)⁰ production in central Pb+Pb, Si+Si, C+C and inelastic p+p collisions at 158A GeV

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Production of the K(892)⁰ and K(892)⁰ resonances was studied via their K+ π- and K- π+ decay modes in central Pb+Pb, Si+Si, C+C and inelastic p+p collisions at 158 (√sNN = 17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum and rapidity distributions were measured and total yields were estimated. The yield of K exceeds that of K by about a factor of two in nucleus-nucleus reactions. The total yield ratios < K >/< K+ > and < K >/< K-> are strongly suppressed in central Pb+Pb compared to p+p, C+C and Si+Si collisions in agreement with the expected attenuation of these short-lived resonance states in the hadronic phase of the expanding fireball. The UrQMD model, although incorporating such a scenario, does not provide a quantitative description of the experimental results. The statistical hadron gas model assuming the same freeze-out parameters for stable hadrons and resonances overestimates the < K >/< K > ratios in central Pb+Pb collisions by about a factor of 2.5.