Antikaon production and medium effects in proton-nucleus reactions at subthreshold beam energies

Abstract

Inclusive K −-meson production in proton-nucleus collisions in the subthreshold-energy regime is analyzed within an appropriate folding model for incoherent primary proton-nucleon and secondary pion-nucleon production processes, which takes properly into account the struck-target-nucleon momentum and removal-energy distribution (nucleon spectral function), novel elementary cross sections for proton-nucleon reaction channels close to threshold, as well as nuclear mean-field potential effects on the one-step and two-step antikaon-creation processes. A detailed comparison of the model calculations of the K − differential cross sections for the reactions p+9Be and p+63Cu at subthreshold energies with the first experimental data obtained at the ITEP proton synchrotron is given. It displays both the relative role of the primary and secondary production channels at incident energies considered and the contributions to K − production that come from the use of the single-particle part and high-momentum-energy part of the nucleon spectral function. It is found that the pion-nucleon production channel does not dominate in the subthreshold “hard” antikaon production in p 9Be and p 63Cu collisions and that the main contributions to the antikaon yields here come from the direct K −-production mechanism. The influence of the nucleon, kaon, and antikaon mean-field potentials on the K − yield is explored. It is shown that the effect of the nucleon mean field is of importance in explaining the considered experimental data on “hard” antikaon production, whereas the K + andK − optical potentials play a minor role. The sensitivity of subthreshold “soft” antikaon production in p 9Be reactions to the nucleon, kaon, and antikaon mean fields is studied. It is demonstrated that, contrary to the case of “hard” antikaon production, the K − potential has a very strong effect on the K − yield, which is comparable with that from the nucleon effective potential.