First Measurement of Near- and Sub-Threshold $J/\psi$ Photoproduction off Nuclei

Abstract

We report on the first measurement of $J/\psi$ 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 $\sim 8.2$ 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 $A(\gamma ,e^{+}{e}^{-}p)$ reaction with a dilepton invariant mass $M(e^{+}{e}^{-})\sim m_{J/\psi }=3.1$ GeV. The incoherent $J/\psi$ 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 $\sqrt{⟨r^2⟩}=0.85\pm 0.14$ 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.

References in corpus (13)

• Probing Cold Dense Nuclear Matter
• Momentum sharing in imbalanced Fermi systems
• Evidence for the Strong Dominance of Proton-Neutron Correlations in Nuclei
• Modified Structure of Protons and Neutrons in Correlated Pairs
• Parton Distributions in Nucleons and Nuclei
• Probing the core of the strong nuclear interaction
• The GlueX Beamline and Detector
• Measurement of the J/$\psi$ photoproduction cross section over the full near-threshold kinematic region
• Generalized Contact Formalism Analysis of the ${}^4$He$(e,e^{\prime }pN)$ Reaction
• The GlueX Start Counter Detector
• Sub-threshold $J/\psi$ and ${\rm Y}$ Production in $\gamma A$ Collisions
• Search for Sub-threshold Photoproduction of J/Psi Mesons
• Subthreshold production of $J/\psi$ mesons from the deuteron with SoLID

Cited by in corpus (1)

• Absorption of 1$P$-wave heavy charmonium ${\chi }_{c1}(1P)$ in nuclei