Gluon gravitational form factors of the proton from the charmonium photoproduction

Abstract

Inspired by the recent J/ψ photoproduction measurements, we discuss the D-term gravitational form factors (GFFs) and the mechanical properties of the proton. Under the assumption of the tripole form, the gluon D-term form factor is determined by fitting the J/ψ differential cross-section data. Combined with the quark D-term form factor extracted from the deeply virtual Compton scattering experiment, the total D-term form factor is obtained to investigate their applications for the description of the mechanical properties. Moreover, the predicted gluon D-term form factor is compared with the existing lattice quantum chromodynamics determinations, which indicates our result is overestimated in momentum transfer |t| < 0.5 GeV 2 . Accordingly, the distributions of pressure and shear forces inside the proton are investigated. Finally, the root-mean-square (rms) proton mechanical radius R 2 mech = 0.86 ± 0.03 fm, while the rms pressure p(0) = 1.42 ± 0.07 GeV/fm 3 in the center of nucleon are calculated. These results provide a unique perspective for studying the gluon D-term form factor of proton and important information for revealing the internal pressure and shear distributions of nucleons.

Colloquium: Gravitational Form Factors of the Proton

“…Phenomenological studies of gluon GFFs have been presented in (Kou et al, 2021;Wang et al, 2022) where the gluon D G (t) form factor of the proton was extracted from J/Ψ threshold photoproduction data. (For remarks on the theoretical status of this process see Sec.…”