Subthreshold antiproton production in pC, dC and  C reactions

Abstract

Abstract. Data from KEK on subthresholdp as well as on π ± and K ± production in pC, dC and αC 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 thep cross section, as well as the moderate increase of meson production in dC and αC 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.

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

“…On the other hand, although the deviations between our calculations and the data are usually less than a factor of 2 or so, there remains room for not too large effects not yet included in the ROC model. As shown in [2] and supported by the present results, the main contribution for subthreshold particle production in conditions of the experiments [3] comes, according to the ROC model, from the excitation of FBs with baryon numbers from 2 to 4. This means that physical properties of such FBs may be directly studied in collisions of proton, deuteron and helium-ion beams with the lightest nuclear targets, 2 H, 3 He and 4 He.…”

“…In [2] we reproduced the observed increase of subthresholdp production in dC and αC reactions compared to pC interactions and demonstrated that within the ROC model the number of participating nucleons is the key quantity for understanding subthreshold particle production. In addition, the whole set of experimental data for all ejectiles measured was well described.…”

“…The mathematical formulation of the above picture is given in [2]. In the following we employ the same parameter set as used in [1,2] for the C target also for the heavier target nuclei except the maximum temperature of the nuclear residues (see section 3).…”

“…As example, figure 1 demonstrates that the basic features of fragment spectra are reasonably reproduced. In [2], we used Θ max R =12 MeV for light nuclei up to C, here Θ max R =10 MeV is taken for Al and Θ max R =6.8 MeV for Ag (see figure 1). For mass numbers above 100 the temperature is assumed to be constant and we take Θ max R =6.8 MeV also for Pb.…”

“…In two recent papers [1,2] we discussed data [3] on p, π ± and K ± production in the reactions pC, dC and αC at energies between 3.5 and 12.0 A GeV within the Rossendorf collision (ROC) model. Special emphasis was on subthreshold production of antiprotons the enormous enhancement of which in dC and αC compared to pC reactions could be well reproduced.…”