Strong Absorption of Hadrons with Hidden and Open Strangeness in Nuclear Matter

Abstract

We present the first observation of ${K}^{\ensuremath{-}}$ and $\ensuremath{\phi}$ absorption within nuclear matter by means of ${\ensuremath{\pi}}^{\ensuremath{-}}$-induced reactions on C and W targets at an incident beam momentum of $1.7\text{ }\text{ }\mathrm{GeV}/c$ studied with HADES at $\mathrm{SIS}18/\mathrm{GSI}$. The double ratio $({K}^{\ensuremath{-}}/{K}^{+}{)}_{\mathrm{W}}/({K}^{\ensuremath{-}}/{K}^{+}{)}_{\mathrm{C}}$ is found to be $0.319\ifmmode\pm\else\textpm\fi{}0.009(\mathrm{stat}{)}_{\ensuremath{-}0.012}^{+0.014}(\mathrm{syst})$ indicating a larger absorption of ${K}^{\ensuremath{-}}$ in heavier targets as compared to lighter ones. The measured $\ensuremath{\phi}/{K}^{\ensuremath{-}}$ ratios in ${\ensuremath{\pi}}^{\ensuremath{-}}+\mathrm{C}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}+\mathrm{W}$ reactions within the HADES acceptance are found to be equal to $0.55\ifmmode\pm\else\textpm\fi{}0.04(\mathrm{stat}{)}_{\ensuremath{-}0.07}^{+0.06}(\mathrm{syst})$ and to $0.63\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{stat}{)}_{\ensuremath{-}0.11}^{+0.11}(\mathrm{syst})$, respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the $\ensuremath{\phi}$ meson in nuclear medium is strongly coupled to the ${K}^{\ensuremath{-}}$ dynamics. The large difference in the $\ensuremath{\phi}$ production off C and W nuclei is discussed in terms of a strong $\ensuremath{\phi}N$ in-medium coupling. These results are relevant for the description of heavy-ion collisions and the structure of neutron stars.