Absorption of $\psi(2S)$ mesons in nuclei

TL;DR

This paper models the near-threshold photoproduction of $(2S)$ mesons in nuclei, analyzing how absorption and nuclear effects influence observable cross sections, aiming to inform future experiments on charmonium suppression and quark-gluon plasma signals.

Contribution

It introduces a collision model incorporating nuclear spectral functions and absorption effects to predict $(2S)$ production observables near threshold energies, providing new insights into charmonium-nucleon interactions.

Findings

Sensitivity of observables to $(2S)N$ absorption scenarios.

Predictions for cross section ratios on different nuclei.

Potential to determine $(2S)N$ absorption cross section in future experiments.

Abstract

In the present work we explore the inclusive $\psi(2S)$ 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 $\psi(2S)$ absorption, target nucleon binding and Fermi motion. We calculate the absolute and relative excitation functions for production of $\psi(2S)$ mesons on $^{12}$C 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$^{\circ}$--10$^{\circ}$, 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 cross sections for $\psi(2S)$ production at photon energy of 13 GeV within the different scenarios for the $\psi(2S)N$ absorption cross section. We also calculate the A-dependence of the ratio of $\psi(2S)$ 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 $\psi(2S)N$ absorption cross section and on its part associated with the nondiagonal process $\psi(2S)+N \to J/\psi+N$ 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.