Investigation of the subthreshold production of $K^-$ mesons in proton-nucleus collisions

The differential cross sections for the proton-induced production of K ⁻ mesons on Be, Al, and Cu nuclei in the subthreshold energy region have been measured. Folding-model calculation including three channels of their production satisfactorily reproduces the experimental data. It has been shown that the main contribution to the production of hard K ⁻ mesons comes from the nonresonant direct process. Evidence for the existence of an attractive optical potential with a magnitude of about 140 MeV for K ⁻ at normal nuclear density has been obtained.