Speakers
Description
Near-threshold charmonium photoproduction opens the door for studying the gluonic properties of the proton: gluonic GPDs, anomalous contribution to the mass of the proton, gravitational form factors, and the mass radius of the proton. However, such an ambitious program requires precise measurements to validate the theoretical assumptions that relate the experimental results to the above quantities. The first total cross-section measurements of near-threshold exclusive $J/\psi $ photoproduction ($\gamma p \rightarrow J/\psi p$) [1] by the GlueX collaboration sparked remarkable theoretical interest, however had limited statistics. We will report new total cross-section results based on more than a four-fold increase in statistics. Even more, due to the full acceptance of the GlueX experiment for this reaction, we will present first measurements of the differential cross-sections over the whole near-threshold kinematic region. Such measurements enable more general quantitative conclusions about the reaction mechanism, when compared to the theoretical calculations that cover a wide range of methods and reaction channels, from gluon exchange to open-charm intermediate states. Prospects of future $J/\psi $ measurements at Jefferson Lab will be discussed, as well.
[1] A. Ali et al. (GlueX collaboration), Phys. Rev. Lett. 123, 072001 (2019).
| speaker affiliation | Jefferson Lab |
|---|
