THE RELATIVISTIC TRANSPORT MODEL DESCRIPTION OF SUBTHRESHOLD KAON PRODUCTION IN HEAVY-ION COLLISIONS

The relativistic transport model, in which the nucleon effective mass is connected to the scalar field while its energy is shifted by the ve ctor potential, is extended to include the kaon degree of freedom. We further take into account the medium modification of the kaon mass due to explicit chiral symmetry breaking. Both the propagation of kaons i n the mean-field potential and the kaon-baryon elastic scattering are explicitly treated in our study. We find that the attractive kaon scal ar mean-field potential in the dense matter leads to an enhanced kaon yield in heavy-ion collisions at energies of about 1 GeV/nucleon that are below the threshold for kaon production from the nucleon-nucleon i nteraction in free space. The final-state kaon-baryon scattering is se en to affect significantly the kaon momentum spectra, leading to an en hanced yield of kaons with large momenta or at large laboratory angles . With a soft nuclear equation of state and including the attractive k aon scalar potential, the calculated kaon energy spectra agree with th e preliminary data on subthreshold kaon production from the heavy-ion synchrotron at GSI.