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

TL;DR

This study investigates strange meson production in Al+Al collisions at 1.9A GeV, highlighting the importance of in-medium modifications and quantifying contributions from phi decays.

Contribution

It provides new measurements of K+, K-, and phi mesons at sub-threshold energies and compares results with transport models to understand in-medium effects.

Findings

In-medium modifications are necessary to match K- and K+ energy distribution ratios.

Phi mesons contribute approximately 17% to K- production.

Results align with previous data at similar energies and systems.

Abstract

The production of K$^+$, K$^-$ and $\varphi$(1020) mesons is studied in Al+Al collisions at a beam energy of 1.9A GeV which is close or below the production threshold in NN reactions. Inverse slopes, anisotropy parameters, and total emission yields of K$^{\pm}$ 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 previous K$^{\pm}$ and $\phi$ data obtained for different colliding systems at similar incident beam energies.