Evidence of kaon nuclear and Coulomb potential effects on soft K + production from nuclei

The ratio of forward K+ production on copper, silver and gold targets to that on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as a function of the kaon momentum pK using the ANKE spectrometer at COSYJülich. The strong suppression in the ratios observed for pK < 200–250 MeV/c may be ascribed to a combination of Coulomb and nuclear repulsion in the K+A system. This opens a new way to investigate the interaction of K+-mesons in the nuclear medium. Our data are consistent with a K+A nuclear potential of V 0 K ≈ 20MeV at low kaon momenta and normal nuclear density. Given the sensitivity of the data to the kaon potential, the current experimental precision might allow one to determine V 0 K to better than 3MeV.