HADES Collaboration

The production of strange mesons in pion-nucleus reactions allows for a quantitative investigation of in-medium effects such as re-scattering or absorption processes at well-defined nuclear density. Overall, $10 \times 10^7$ and $13 \times 10^7$ events have been collected with the HADES detector at the GSI pion beam facility in $\pi^-+C$ and $\pi^-+W$ collisions at $p_{\pi^-}= 1.7$ GeV/$c$. We present our results on the open and hidden strange meson ($K^{\pm}$ and $\phi$) production in cold nuclear matter. Special emphasis will be put on the study of $K^-$ absorption driven by strangeness exchange processes on one ($K^- N\rightarrow Y\pi$) or more nucleons ($K^- NN\rightarrow YN$). The data supports $K^-$ absorption in the heavier system (W) by comparing the $K^-/K^+$ ratios measured in collisions with heavy targets (W) and lighter ones (C). In addition, the $\phi$ absorption in nuclear medium will be addressed by comparing the production in both nuclear environments as well as the $\phi$ feed-down to the $K^-$ production.

Work supported by the DFG cluster of excellence "Origin and Structure of the Universe" and SFB 1258.