Subthreshold production of K+ mesons and the fragmentation of the target nucleus

Abstract

Abstract.The interplay between subthreshold K+-production and the fragmentation of the target nucleus is considered in proton-nucleus interactions at projectile energies between 0.8 and 1 GeV. Inclusive data for the production of K + mesons and of fragments are well described in the framework of the modified phase space model. For a coincidence measurement between K + mesons and fragments the model predicts a decrease of the relative yield of intermediate mass fragments by about four orders of magnitude. This strong decrease is a consequence of energy-momentum conservation, because at subthreshold energies a second endothermic process like multifragmentation can hardly proceed simultaneously with the K + production. A K + meson is, therefore, expected to be accompanied by a heavy target residue, which is so weakly excited that it may evaporate a few nucleons but cannot decay into fragments. Due to the large energy and momentum transfer in this process the strength of the predicted effect is supposed to be sensitive to the details of the reaction dynamics.

ForwardK+Production in SubthresholdpACollisions at 1.0 GeV

“…Total cross sections have been measured at the Petersburg Nuclear Physics Institute (PNPI) synchrocyclotron for targets between Be and Pb and projectile energies T p from 0.8 to 1.0 GeV [1]. The results were discussed in terms of different models [1][2][3][4][5], in particular, of single-or two-step reactions involving the creation of an intermediate pion. It was concluded that additional experimental data were needed for an unambiguous determination of the reaction mechanism and the extraction of the information on nuclearmedium effects.…”

“…A high degree of collectivity is needed in the target nucleus to allow K 1 production far below the free NN threshold; i.e., the number of target nucleons involved must be significantly larger than 1 [1][2][3][4][5]. Alternatively, high in- trinsic momenta of the participating target nucleon(s) are required to supply the missing energy for subthreshold kaon production.…”

Phenomenological analysis ofK+-meson production in proton-nucleus collisions

“…the formation of clusters in the target nucleus) [9] or is a reflection of a high degree of collectivity in the target nucleus [5]. We expect that such effects are proportional to the number of target nucleons and, therefore, the cross section should scale as ≃A 1 .…”

“…The results were discussed in terms of different models [1,8,9,10,11], in particular of single or two-step reactions, the latter with the creation of an intermediate pion. It has been argued that the dependence of the K + -production cross section on the target mass A is sensitive on the mechanism dominantly contributing to kaon production.…”

Soft hadron production in pp interactions up to ISR energies

“…The Rossendorf collision (ROC) model [11,12,13,14,15,16,17] is basically a statistical approach in deriving the relative contributions of the various final channels by calculating their statistical weights from the phase-space factors, which are, however, strongly modified by empirical transition matrix elements. It aims at describing soft hadron production in the energy region between particle production thresholds and ISR energies.…”