Antiproton Production in \(p+A\) Collisions at AGS Energies

Inclusive and semi-inclusive measurements are presented for antiproton (\(\bar{p}\)) production in proton-nucleus collisions at the AGS. The inclusive yields per event increase strongly with increasing beam energy and decrease slightly with increasing target mass. The \(\bar{p}\) yield in 17.5 GeV/c p+Au collisions decreases with grey track multiplicity, \(N_g\), for \(N_g>0\), consistent with annihilation within the target nucleus. The relationship between \(N_g\) and the number of scatterings of the proton in the nucleus is used to estimate the \(\bar{p}\) annihilation cross section in the nuclear medium. The resulting cross section is at least a factor of five smaller than the free \(\bar{p}-p\) annihilation cross section when assuming a small or negligible formation time. Only with a long formation time can the data be described with the free \(\bar{p}-p\) annihilation cross section.