International Conference on Exotic Atoms and Related Topics - EXA2017

The production and properties of open and hidden strange hadrons ($K^+$, $K^-$ and $\phi$) in cold nuclear matter generated in pion-nucleus reactions ($\pi^- + A$, $A = C, W$) at $p_{\pi^-}= 1.7$~GeV/c has been investigated with the HADES setup (SIS18/GSI).\\ Exploring the modification of the (anti-)kaon spectral function in nuclear matter which should be already apparent at finite baryon densities is of particular interest. While, for the kaon ($K^+, K^0$) the repulsive $KN$-potential has been studied to some extent having a moderate strength ($20-40$~MeV), the existing data on in-medium effects of the antikaon produced off nuclear targets are very scare. Moreover, the $K^-$ can be absorbed in nuclear medium which should be driven by strangeness exchange processes on one ($K^- N\rightarrow Y\pi$) or more nucleons ($K^- NN\rightarrow YN\pi$). On the contrary, $K^+$ is not affected by strong absorption processes and can be treated as a quasi particle within nuclear matter, providing stringent constraints on the production mechanism of strange hadrons. In this context, also the $\phi$ production and absorption ($\phi\rightarrow K^+ K^-$, $BR \sim 48.9$\%) off light and heavy nuclear targets is studied.\\ In this talk, we are presenting evidence of the $K^-$ absorption on the basis of the $K^-/K^+$ ratios in both nuclear environments (C, W). In addition, the $\phi$ absorption in a nuclear medium is discussed by comparing the production off carbon and tungsten as well as the $K^-$ production in terms of the $\phi$ feed-down. \newline \newline * supported by the DFG cluster of excellence "Origin and Structure of the Universe" and SFB 1258