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

We present the first observation of K- and ϕ absorption within nuclear matter by means of π--induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K-/K+)W/(K-/K+)C is found to be 0.319±0.009(stat)+0.014-0.012(syst) indicating a larger absorption of K- in heavier targets as compared to lighter ones. The measured ϕ/K- ratios in π-+C and π-+W reactions within the HADES acceptance are found to be equal to 0.55±0.04(stat)+0.06-0.07(syst) and to 0.63±0.06(stat)+0.11-0.11(syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the ϕ meson in nuclear medium is strongly coupled to the K- dynamics. The large difference in the ϕ production off C and W nuclei is discussed in terms of a strong ϕN in-medium coupling. These results are relevant for the description of heavy-ion collisions and the structure of neutron stars. [ABSTRACT FROM AUTHOR]