Subthreshold K--meson production in proton-nucleus reactions revisited

Abstract

The inclusive K−-meson production in proton-nucleus collisions in the subthreshold energy regime is studied in the framework of an appropriate spectral function approach for incoherent primary proton-nucleon and secondary pion-nucleon production processes, which takes properly into account the nuclear mean-field potential effects on these processes as well as the final state interaction (FSI) among the outgoing nucleons participating in the one-step antikaon creation process. A detailed comparison of the model calculations of the K− differential cross sections is given for the reactions p + 9Be, p + 63Cu, and p + 197Au at subthreshold energies with the currently available experimental data obtained recently at the ITEP proton synchrotron and at SIS/GSI. It is found that the calculations with inclusion of the influence of both the nuclear density-dependent mean-field potentials and the elementary NN-FSI effects on the K− production from direct mechanism are able to reproduce, contrary to previous estimates based on the use only of the density-dependent mean fields in calculating the K− yield from this mechanism, the energy dependences of the invariant differential cross sections for “hard” antikaon creation in p9Be and p63Cu collisions. It is further shown that the NN-FSI effects play a minor role in describing the data on the spectrum of relatively soft K− mesons from p197Au interactions at incident energy of 2.5 GeV. It is also shown that the relative strength of the proton-and pion-induced reaction channels in the subthreshold energy regime is governed by the kinematics of the experiment under consideration. The influence of the nucleon, kaon, and antikaon mean-field potentials on the K− yield is explored. It is demonstrated that, in line with previous findings, the K− optical potential has a strong effect on this yield at low antikaon momenta, which is greater than those from nucleon and kaon effective potentials. At high antikaon momenta, the K− yield is found to be mainly determined, along with the elementary NN-FSI effects, by the nucleon mean field and the scenario with zero K+ potential is favorable.