Genuine empirical pressure within the proton

TL;DR

This paper presents a novel method to extract the transverse light front pressure densities inside the proton, revealing the internal force distribution and a smaller mechanical radius compared to the charge radius.

Contribution

It introduces a relativistic approach to determine the proton's internal pressure distribution using light front dynamics, improving upon previous Breit frame methods.

Findings

Mechanical radius estimated at 0.518 fm

Forces are predominantly repulsive within 0.43 fm

Forces become predominantly attractive beyond 0.43 fm

Abstract

A phenomenological extraction of pressure within the proton has recently been performed using JLab CLAS data (arXiv:2104.02031 [nucl-ex]). The extraction used a 3-dimensional Breit frame description in which the initial and final proton states have different momenta. Instead, we obtain the two-dimensional transverse light front pressure densities that incorporate relativistic effects arising from the boosts that cause the initial and final states to differ. The mechanical radius is then determined to be $0.518~ \pm 0.062_{\mathrm{fit}} \pm 0.126_{\mathrm{sys}}~\mathrm{fm}$, which is smaller than the electric charge radius and larger than the light front momentum radius. The forces within the proton are shown to be predominantly repulsive at distances less than $0.43~\pm 0.12~\mathrm{fm}$ from the center, and predominantly attractive further out.