Antiproton Production in p + d Reaction at Subthreshold Energies

An enhancement of antiprotons produced in the p+dreaction in comparison over those produced in the p+p elementary reaction is investigated. In the neighborhood of the subthreshold energy, the enhancement is caused by the difference in threshold energies for antiproton production. The cross section of the p+d reaction, on the other hand, becomes just twice that in the elementary p + p reaction at the incident energy far from the threshold energy when non-nucleon components in the deuteron target are not considered.