Near-Threshold J/$\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ Photoproduction and the Gluonic Gravitational Form Factors of the Proton

Abstract

We report on the measurement of the two-dimensional differential cross section for near-threshold J/$\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ photoproduction from the J/$\ddot{I}ˆ$-007 experiment in Hall C at Jefferson Lab. Our results agree with the previously published J/$\ddot{I}ˆ\to e^{+}{e}^{-}$ results. We extract the integrated photoproduction cross section and find no evidence for open-charm contributions. A combined analysis of both decay channels following a Holographic QCD approach yields improved experimental constraints on the gluonic gravitational form factor ${\mathcal{C}}_g(t)$. Our results agree with recent lattice QCD calculations and we obtain ${\mathcal{C}}_g(t)$ with a comparable statistical precision to lattice QCD. Our results support a spatial picture where gluons dominate at larger radii with a confining inward pressure. This work provides new input for exploring the mechanical properties of gluons inside the proton.