Medium Modifications of the Rho Meson in Nuclear Photoproduction

TL;DR

This paper investigates how rho mesons behave inside nuclei during photon-induced reactions, analyzing dilepton spectra and nuclear transparency to understand medium modifications of the rho spectral function.

Contribution

It extends previous work by analyzing additional observables and comparing theoretical predictions with recent experimental data from CLAS, focusing on medium effects on the rho meson.

Findings

Spectral shape varies with target nucleus and lepton pair momentum.

Nuclear transparency ratios provide consistent estimates of in-medium rho width.

Results support the presence of medium modifications to the rho spectral function.

Abstract

We extend our recent study of dilepton invariant-mass spectra from the decays of rho mesons produced by photon reactions off nuclei. We specifically focus on experimental spectra as recently measured by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility using carbon and iron nuclei. Building on our earlier work we broaden our description to a larger set of observables in order to identify sensitivities to the medium effects predicted by microscopic calculations of the rho spectral function. We compute mass spectra for several target nuclei and study the spectral shape as a function of the 3-momentum of the outgoing lepton pair. We also compute the so-called nuclear transparency ratio which provides an alternative means (and thus consistency check) of estimating the inelastic rho width in the cold nuclear medium.