Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

Abstract

The production of non-φ K + K − pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K − momentum dependence of the differential cross section has been measured for laboratory polar angles θ K ± ≤ 12 • over the 0.2-0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K − -nucleus potential of about −60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K − momenta.

Meson–nucleus potentials and the search for meson–nucleus bound states

“…Since the actual magnitude of the antikaon scalar potential, entering into the dispersion relation (53) through the Eq. (54), is not reliably known also at finite momenta (see Section 4.3.2), it has been adopted in the momentum-independent form (56) or is treated as a free parameter to be extracted in the analysis of inclusive [64,166] and exclusive [167] data on K − production in pA collisions, taken at the ITEP/Moscow and COSY/Jülich accelerators, in the framework of the nuclear spectral function approach [77,78,86]. We note in passing that the "free particle" dispersion relation (53) for the K − energy in matter with the effective momentum-independent antikaon mass (and momentum-independent scalar potential V K − )…”

“…The in-medium modifications of K − meson properties have also been studied experimentally in proton-nucleus reactions at beam energies close to or below the production threshold in N N collisions over the last years (see, for example, [46,58,64,166,167]). The advantage of such reactions compared to heavy-ion collisions is that the processes of hadron production and propagation proceed in cold static nuclear matter of well-defined density at zero temperature.…”

“…Such measurements have recently been performed by the ANKE Collaboration at the COSY/Jülich accelerator, where the production of K + K − pairs with invariant masses corresponding to both the non-φ [167] and φ [182,183] regions (see also Section 4.7 below) has been studied in proton collisions with C, Cu, Ag, and Au targets at an initial beam energy of 2.83 GeV. The K − momentum dependence of the coincident differential cross section has been measured for laboratory polar angles θ K ± ≤ 12 • over the momentum range of 0.2-0.9 GeV/c for these four target nuclei.…”

“…On the other hand, the data at lower antikaon momenta are described reasonably well with almost no K − potential and are overestimated by all the calculations with a nonzero antikaon potential. This suggests [167] that the model misses some aspects of the absorption of low-momentum K − mesons and/or their production in nuclear matter. Fig.…”

“…The figure is taken from [167]. Therefore, to determine the antikaon nuclear potential, the ratio of the measured, momentum integrated K − cross section for the nonresonant K + K − pair production on a given nucleus A to the corresponding cross section calculated within the model for different potential strengths, has been considered in [167], rather than the differential cross sections themselves, which are shown in Fig. 31.…”