Extraction of the proton mass radius from the vector meson photoproductions near thresholds

TL;DR

This paper extracts the proton mass radius by analyzing vector meson photoproduction near thresholds, linking the process to the proton's scalar gravitational form factor and QCD trace anomaly, resulting in a measured radius of approximately 0.67 fm.

Contribution

It introduces a method to determine the proton mass radius from near-threshold vector meson photoproduction data, connecting experimental observables to the proton's scalar form factor.

Findings

Proton mass radius estimated at 0.67±0.03 fm.

Scalar form factor modeled with a dipole form with cutoff 1.01±0.04 GeV.

Method links photoproduction data to the proton's mass distribution.

Abstract

We present an analysis of the proton mass radius by studying the $t$-dependence of the differential cross sections of the vector meson photoproductions near the thresholds. At low energy, the photoproduction of a quarkonium off the proton is connected to the scalar gravitational form factor of the proton, which is sensitive to the proton mass distribution from the QCD trace anomaly. Under an assumption of the scalar form factor of dipole form, the proton mass radius is extracted via the near-threshold photoproduction data of J/$\psi$, $\phi$ and $\omega$ vector mesons. The average value of the proton mass radius is estimated to be $\sqrt{\left<R_{\rm m}^2\right>} = 0.67\pm0.03$ fm, with the dipole cutoff $m_{\rm s}=1.01\pm0.04$ GeV.