Gluonic Energy Momentum Tensor Form Factors of the Proton

Abstract

Gravitational form factors (GFFs), defined through the matrix elements of the energy-momentum tensor, provide critical insights into the internal structure of nucleons and nuclei. In particular, their Fourier transforms -- evaluated in the Breit frame -- reveal spatial distributions of mass, pressure, and shear force densities associated with both quark and gluon constituents. This work presents recent measurements of near-threshold $J/\psi$ photoproduction on the proton, performed in Hall C at Jefferson Lab, utilizing data from the electronic decay channels of the $J/\psi$. These results enable the extraction of gluonic gravitational form factors (gGFFs), offering a novel probe of the gluon dynamics within the nucleon. The analysis employs a holographic QCD framework to interpret the threshold behavior of the cross sections and to facilitate the extraction of the gGFFs. The implications of these measurements are discussed in the context of upcoming experimental programs, including the near-threshold electro- and photoproduction studies with SoLID at Jefferson Lab and the $\Upsilon$ production program at the Electron-Ion Collider using the ePIC detector. These future efforts are expected to significantly improve the precision of gGFF determinations and provide essential tests of their universality across different kinematic regimes.