Momentum dependence of near-threshold photoproduction of Ξ− hyperons off nuclei and their properties in the nuclear medium

Abstract

We study the near-threshold inclusive photoproduction of Ξ− hyperons off 12C and 184W target nuclei within a first-collision model relying on the nuclear spectral function and including incoherent Ξ− production in direct elementary γp→K+K+Ξ− and γn→K+K0Ξ− processes. The model takes into account the impact of the nuclear effective scalar K+, K0, Ξ− and their Coulomb potentials on these processes as well as the absorption of final Ξ− hyperons in nuclear matter, the binding of intranuclear nucleons and their Fermi motion. We calculate the absolute differential cross sections and their ratios for the production of Ξ− hyperons off these nuclei at laboratory polar angles ≤ 45∘ by photons with energies of 2.5 and 3.0 GeV, with and without imposing the phase space constraints on the Ξ− emission angle in the respective γp center-of-mass system. We also calculate the momentum dependence of the transparency ratio for Ξ− hyperons for the 184W/12C combination at these photon energies. We show that the Ξ− momentum distributions (absolute and relative) at the adopted initial photon energies possess a definite sensitivity to the considered changes in the scalar Ξ− nuclear mean-field potential at saturation density ρ0 in the low-momentum range of 0.1–0.8 GeV/c. This would permit evaluating the Ξ− potential in this momentum range experimentally. We also demonstrate that the momentum dependence of the transparency ratio for Ξ− hyperons for both photon energies can hardly be used to determine this potential reliably. Therefore, the precise measurements of the differential cross sections (absolute and relative) for inclusive Ξ− hyperon photoproduction on nuclei near threshold in a dedicated experiment at the CEBAF facility will provide valuable information on the Ξ− in-medium properties, which will be supplementary to that inferred from studying of the (K−,K+) reactions at initial momenta of 1.6–1.8 GeV/c.