Strange meson production in Al+Al collisions at 1.9 A GeV

The production of K+, K- and \( \phi\) (1020) mesons is studied in Al+Al collisions at a beam energy of 1.9A GeV which is close to or below the production threshold in NN reactions. Inverse slopes, anisotropy parameters, and total emission yields of K± mesons are obtained. A comparison of the ratio of kinetic energy distributions of K- and K+ mesons to the HSD transport model calculations suggests that the inclusion of the in-medium modifications of kaon properties is necessary to reproduce the ratio. The inverse slope and total yield of \( \phi\) mesons are deduced. The contribution to K- production from \( \phi\) meson decays is found to be \( [17 \pm 3(stat)^{+2}_{-7}(syst)]\)%. The results are in line with the previous K± and \( \phi\) data obtained for different colliding systems at similar incident beam energies.