Subthreshold antiproton production in pC, dC and $\alpha$C reactions

Data from KEK on subthreshold antiproton as well as on charged pion and kaon production in pC, dC and $\alpha$C reactions at energies between 3.5 and 12.0 A GeV are described for the first time within a unified approach. We use a model which considers a nuclear reaction as an incoherent sum over collisions of varying numbers of projectile and target nucleons. It samples complete events and thus allows for the simultaneous consideration of all final particles including the decay products of the nuclear residues. The enormous enhancement of the antiproton cross section as well as the moderate increase of meson production in dC and $\alpha$C compared to pC reactions is well reproduced. In our approach, the observed enhancement near the production threshold is mainly due to the contributions from the interactions of few-nucleon groups.