Kaon production in Au+Au collisions at11.6A GeV/c

A systematic study of the spectra and yields of $K^{+}$ and $K^{-}$ is reported by experiment E866 as a function of centrality in Au+Au collisions at $11.6A\hspace{0.5em}\mathrm{GeV}/c.\mathrm{}$ The invariant transverse spectra for both kaon species are well described by exponentials in $m_t,$ with inverse slope parameters that are largest at midrapidity and which increase with centrality. The inverse slopes of the $K^{+}$ spectra are slightly larger than the inverse slopes of the $K^{-}$ spectra. The kaon rapidity density peaks at midrapidity with the $K^{+}$ distribution wider in rapidity than $K^{-}.$ The integrated total yields of $K^{+}$ and $K^{-}$ increase nonlinearly and steadily with the number of projectile participants. The yield per participant for kaons is two to three times larger than the yield from $N-N$ collisions. This enhancement suggests that the majority of kaons in central Au+Au reactions are produced in secondary hadronic collisions. There is no evidence for an onset of additional kaon production from a possible small volume of baryon-rich quark-gluon plasma. The differences between $K^{+}$ and $K^{-}$ rapidity distributions and transverse spectra are consistent with a lower phase space for $K^{-}$ production due to a higher energy threshold. These differences also exclude simple thermal models that assume emission from a common equilibrated system.