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 $γp \to K^+{K^+}Ξ^-$ and $γn \to K^+{K^0}Ξ^-$ 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 $\le$ 45$^{\circ}$ 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 $^{184}$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, contrary to the transparency ratio for $Ξ^-$ hyperons, 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. Therefore, the precise measurements of these distributions 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.