Subthreshold antiproton production in nucleus-nucleus collisions

Antiproton production in nucleus-nucleus collisions at energies below the threshold for its production from the nucleon-nucleon interaction in free space is studied in the relativistic Vlasov-Uehling-Uhlenbeck model. The antiproton self-energies in the medium are obtained in the mean-field approximation from the G-parity transformation of the nucleon self-energies. Due to the decrease of antiproton mass in the medium as a result of the attractive scalar mean field, there is an enhanced production of primordinal antiprotons which are, however, mostly annihilated by nucelons as they propagate through the matter. The calculated final antiproton momentum spectrum is seen to agree reasonably with the experimental data.