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 12 C and 184 W 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 + K 0 Ξ − processes. The model takes into account the impact of the nuclear effective scalar K + , K 0 , 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 centerof-mass system. We also calculate the momentum dependence of the transparency ratio for Ξ − hyperons for the 184 W/ 12 C 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 ρ 0 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.