Absorption of ψ(2S) mesons in nuclei

Abstract

In the present work we explore the inclusive $\psi \left(2S\right)$ meson photoproduction from nuclei near the kinematic threshold within the collision model, based on the nuclear spectral function, for incoherent direct photon–nucleon charmonium creation processes. The model takes into account the final $\psi \left(2S\right)$ absorption, target nucleon binding and Fermi motion. We calculate the absolute and relative excitation functions for production of $\psi \left(2S\right)$ mesons on ¹²C and ¹⁸⁴ W target nuclei at near-threshold photon beam energies of 8.0–16.4 GeV, the absolute momentum differential cross sections for their production off these target nuclei at laboratory polar angles of 0^∘–10^∘, the momentum dependence of the ratio of these cross sections as well as the A-dependences of the ratios (transparency ratios) of the total cross sections for $\psi \left(2S\right)$ production at photon energy of 13 GeV within the different scenarios for the $\psi \left(2S\right)N$ absorption cross section. We also calculate the A-dependence of the ratio of $\psi \left(2S\right)$ and $J/\psi$ photoproduction transparency ratios at photon energies around of 11.5 GeV within the adopted scenarios for this cross section. We demonstrate that both the absolute and relative observables considered reveal a definite sensitivity to these scenarios. Therefore, the measurement of such observables in future experiments at the upgraded up to 22 GeV CEBAF facility in the near-threshold energy region might shed light both on the $\psi \left(2S\right)N$ absorption cross section and on its part associated with the nondiagonal process $\psi \left(2S\right)+N\to J/\psi +N$ at finite momenta, which are of crucial importance in understanding of charmonium production and suppression in high-energy nucleus–nucleus collisions in a search for the quark-gluon plasma.