Antiproton production in relativistic Si-nucleus collisions

We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/c per nucleon ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.