K+ Production in the System Ni+Ni at an Incident Energy of 1.93 AGeV

Abstract

The investigation of K+ production in heavy ion collisions is interesting for several reasons. Relativistic transport model calculations for nucleus nucleus collisions indicate, that the yield and spectra of kaons are very sensitive to the nuclear equation of state (EOS)[1]. Because of the relative weak K+-nucleon interaction (≈ 10 mb), the measurement of K+ mesons from heavy-ion collisions has thus been considered a promising way to probe not only the dense matter formed in the initial stage of the collision, when kaons are most likely to be produced [2, 3], but also the kaon properties in dense nuclear matter. Kaons might be subject to medium modifications. According to RBUU calculations of G. Q. Li and C. M. Ko [4] the maximum density reached in a Ni+Ni collision at 1.93 AGeV beam energy is about 3. Furthermore, the K+ mass grows less than 10%, the K− mass is reduced by 50% in this density range. This change is driven by the kaon potential in nuclear matter which is density dependent and has its origin in explicit chiral symmetry breaking. Kaon directed sideward flow has been proposed as an additional and even more sensitive probe than the yield for determining the in medium kaon potential [5, 4]. In addition, the yield is influenced by multistep processes, the ratio K+/π+ might be a sensitiv probe for resonance contributions to kaon production [6]. These probes (among others) remain to be very interesting as one proceeds to higher energies (AGS, SPS, RHIC, LHC) as new physics questions become relevant, for example verifying the phase transition of hadronic matter to the quark gluon plasma [7].