Medium effects in K⁺ nuclear interactions

Total (σ_Υ) and reaction (σ_R) cross sections are derived self-consistently from the attenuation cross sections measured in transmission experiments at the AGS for K⁺ on ⁶Li, C, Si and Ca in the momentum range of 500-700 MeV/c by using a V_opt = t_eff(ρ)ρ optical potential. Self-consistency requires, for the KN in-medium t matrix, that Imt t_eff(ρ) increases linearly with the average nuclear density in excess of a threshold value of 0.088 ± 0.004 fm^-3. The density dependence of Re t_eff(ρ) is studied phenomenologically, and also applying a relativistic mean field approach, by fitting to the σ_T and σ_R values. The real part of the optical potential is found to be systematically less repulsive with increasing energy than expected from the free-space repulsive KN interaction. When the elastic scattering data for ⁶Li and C at 715 MeV/c are included in the analysis, a tendency of Re V_opt to generate an attractive pocket at the nuclear surface is observed.