Gravitational form factors of the proton from near-threshold vector meson photoproduction

We systematically analyze the quark and gluon gravitational form factors(GFFs)of the proton by connecting the energy-momentum tensor and near-threshold vector meson photoproduction(NTVMP).Specifically,the quark contributions of GFFs are determined by applying global fitting to the cross section of the lightest vector mesonρ0 photoproduction.Combined with the gluon GFFs obtained from heavy quarkonium J/ψphotoproduction data,the complete GFFs are obtained and compared with the experimental results and lattice quantum chromodynamics determinations.In addition,we use the resonance via Padé(RVP)method based on the Schlessinger point method to obtain a model-independent quark D-term distribution through direct analytical continuation of deeply virtual Compton scattering experimental data.If errors are considered,the results obtained with RVP are essentially consistent with those obtained by NTVMP.Moreover,the comprehensive information on GFFs helps to uncover the mass distribution and mechanical properties inside the proton.This study is not only an important basis for delving into the enigmatic properties of the proton,but also has significance for theoretically guiding future JLab and EIC experimental measurements.

Gluon gravitational form factors of protons from charmonium photoproduction

Inspired by the recent near-threshold J/ψphotoproduction measurements,we discuss gluon gravitational form factors(GFFs)and internal properties of the proton.This work presents a complete analysis of the proton gluon GFFs connecting the gluon part of the energy-momentum tensor and the heavy quarkonium photoproduction.In particular,a global fitting of the J/ψdifferential and total cross section experimental data is used to determine the gluon GFFs as functions of the squared momentum transfer t.Combined with the quark contributions to the D-term form factor extracted from the deeply virtual Compton scattering experiment,the total D-term is obtained to investigate their applications in describing the proton mechanical properties.These studies provide a unique perspective on investigating the proton gluon GFFs and important information for enhancing QCD constraints on the gluon GFFs.

First extraction of the proton mass radius and scattering length |αρ0p|from ρ^(0) photoproduction

As it involves the lightest physical states excited from the vacuum by the vector quark current,near-threshold ρ^(0)photoproduction is considered a possible way to research the proton radius and the absolute value of the scattering lengths of the ρ^(0)-proton interaction.In this study,under the assumption of a scalar form factor of dipole form,the value of the proton mass radius is calculated as(0.85±0.06) fm by fitting the differential cross section of the γp→ρ^(0)p reaction at near-threshold energy.For light vector meson photoproduction,because the exchange of a scalar quark-antiquark pair is not suppressed and should dominate the scalar gluon exchange,the radius we extract from ρ^(0)photoproduction is likely to represent the quark radius of the proton.This fact may explain why the value obtained in this study is very near the proton charge radius.Moreover,the absolute value of the ρ^(0)-proton scattering length |αρ^(0)p|=(0.31±0.06) fm is obtained for the first time within the vector meson dominance model.This result disobeys the rule that the absolute value of the vector meson and proton scattering length |αVp| increases with the meson’s mass,which can be attributed to treating the ρ^(0)meson as a point in the analysis.These results provide useful theoretical information for an in-depth understanding of proton structure and the proton-vector meson interaction.