- th / 9 40 60 30 v 1 2 5 Ju n 19 94 SUNY - NTG 94 - 27 K − - proton scattering and the Λ ( 1405 ) in dense matter

The scattering of antikaons with nucleons is studied in the nuclear environment. Describing the Λ(1405) as a K− proton bound state, we find, that due to the Pauli blocking of intermediate states, the mass of the Λ(1405) is shifted upwards in energy, above the K− proton threshold and and its width is somewhat broadened. As a consequence the s-wave K−–nucleon scattering length turns attractive at finite nucleon density (ρ ≥ 0.25ρ0) leading to a mean field potential for the K− of about ∼ −100MeV in nuclear matter at ground state density. Consequences for Heavy Ion collisions and possible experimental checks for the structure of the Λ(1405) are discussed