2024/09/27 by Pybus, J. R., Ehinger, L., Kolar, T. +65 · 1 citation
#FOS: Physical sciences #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2409.18463
We report on the first measurement of J/ψ photoproduction from nuclei in the photon energy range of 7 to 10.8 GeV, extending above and below the photoproduction threshold in the free proton of ∼8.2 GeV. The experiment used a tagged photon beam incident on deuterium, helium, and carbon, and the GlueX detector at Jefferson Lab to measure the semi-inclusive A(γ,e+e-p) reaction with a dilepton invariant mass M(e+e-)∼ mJ/ψ=3.1 GeV. The incoherent J/ψ photoproduction cross sections in the measured nuclei are extracted as a function of the incident photon energy, momentum transfer, and proton reconstructed missing light-cone momentum fraction. Comparisons with theoretical predictions assuming a dipole form factor allow extracting a gluonic radius for bound protons of √(⟨ r2⟩)=0.85±0.14 fm. The data also suggest an excess of the measured cross section for sub-threshold production and for interactions with high missing light-cone momentum fraction protons. The measured enhancement can be explained by modified gluon structure for high-virtuality bound-protons.