Phi meson production in heavy-ion collisions at SIS energies

Phi meson production in heavy-ion collisions at SIS/GSI energies (∝2 GeV/nucleon) is studied in the relativistic transport model. We include contributions from baryon-baryon, pion-baryon, and kaon-antikaon collisions. The cross sections for the first two processes are obtained in a one-boson-exchange model, while that for the last process is taken to be of Breit-Wigner form through the phi meson resonance. The dominant contribution to phi meson production in heavy-ion collisions at these energies is found to come from secondary pion-nucleon collisions. Effects due to medium modifications of kaon masses, which are needed to account for the observed enhancement of antikaon yield, are also studied and are found to reduce the phi meson yield by about a factor of two, mainly because of an increased phi decay width as a result of dropping kaon-antikaon masses. In this case, the φ/K- ratio is about 4%, which is a factor of 2-3 below preliminary experimental data from the FOPI collaboration at GSI. Including also the reduction of the phi meson mass in medium increases this ratio to about 8%, which is then in reasonable agreement with the data. (orig.)