Target mass number dependence of subthreshold antiproton production in proton-, deuteron- and alpha-particle-induced reactions

Data from KEK on subthreshold \bar{\mrm{p}} as well as on $\pi^\pm$ and \mrm{K}^\pm production in proton-, deuteron- and $\alpha$-induced reactions at energies between 2.0 and 12.0 A GeV for C, Cu and Pb targets are described 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 \bar{\mrm{p}} cross section, as well as the moderate increase of meson production in deuteron and $\alpha$ induced compared to proton-induced reactions, is well reproduced for all target nuclei. In our approach, the observed enhancement near the production threshold is mainly due to the contributions from the interactions of few-nucleon clusters by simultaneously considering fragmentation processes of the nuclear residues. The ability of the model to reproduce the target mass dependence may be considered as a further proof of the validity of the cluster concept.Comment: 9 pages, 4 figure

Energy dependence of multi-pion production in high-energy nucleus-nucleus collisions

Exclusive pi - and charged-particle production in collisions of Ar+KCl is studied at incident energies from 0.4 to 1.8 GeV/u. Complete disintegration of both nuclei is observed. The correlation between pi - and total charge multiplicity shows no islands of anomalous pion production. For constant numbers of proton participants the pi - multiplicity distributions are Poissons. For central collisions increases smoothly and to first order linearly with the c.m. energy. Disagreement with the firestreak model is found. Pacs numbers: 25.70.Hi, 24.10.D

Observation of high-momentum protons from limiting target fragmentation

Measurements of the inclusive distributions of protons produced at 180{sup o} in the momentum range 0.3 {le} p {le} 1.0 GeV/c are reported. Proton, {alpha}-particle, carbon, and argon beams in the range of kinetic energies 0.4 {le} T {le} 2.1 GeV/nucleon (4.89 GeV for protons) were incident on C, Al, Cu, Sn, and Pb targets. The dependences of the cross sections on the projectile and target mass and on the incident energy are presented. Limiting behavior is found at energies above 1-2 GeV/nucleon. Features suggestive of nuclear correlations are discussed