Kaon and Phi Production in Pion-Nucleus Reactions at 1.7 GeV/c*

The production and properties of K+, K− and ϕ in nuclear reactions π− + A (A = C,W) at a beam momentum of 1:7 GeV/c has been studied with the HADES setup at SIS18/GSI. Of particular interest is the K− absorption in nuclear matter which should be driven by strangeness exchange processes on one (K−N → Yπ) or more nucleons (K−NN → YNπ). In this context, also the ϕ has to be taken into account, since ϕ decays into K+K− pairs may substantially affect the measured K− abundance. A solid reference is needed to evaluate the K− absorption with in the nucleus and in this work we discuss the determination of this reference. A double ratio of K−=K+(W)=K−=K+(C) is measured within the acceptance and compared to the reference