Extraction of the proton radius from electron-proton scattering data

TL;DR

This paper presents a new, model-independent analysis of electron-proton scattering data to accurately determine proton radii, revealing discrepancies with muonic hydrogen measurements and discussing potential sources of systematic errors.

Contribution

It introduces an improved analysis method that rebins data and avoids certain assumptions, providing more reliable proton radius estimates from scattering data.

Findings

Proton electric radius from Mainz data: 0.895(20) fm

Proton magnetic radius from Mainz data: 0.776(38) fm

Combined charge radius: 0.904(15) fm, larger than muonic hydrogen value

Abstract

We perform a new analysis of electron-proton scattering data to determine the proton electric and magnetic radii, enforcing model-independent constraints from form factor analyticity. A wide-ranging study of possible systematic effects is performed. An improved analysis is developed that rebins data taken at identical kinematic settings, and avoids a scaling assumption of systematic errors with statistical errors. Employing standard models for radiative corrections, our improved analysis of the 2010 Mainz A1 Collaboration data yields a proton electric radius $r_E = 0.895(20)$ fm and magnetic radius $r_M = 0.776(38)$ fm. A similar analysis applied to world data (excluding Mainz data) implies $r_E = 0.916(24)$ fm and $r_M = 0.914(35)$ fm. The Mainz and world values of the charge radius are consistent, and a simple combination yields a value $r_E = 0.904(15)$ fm that is $4\sigma$ larger than the CREMA Collaboration muonic hydrogen determination. The Mainz and world values of the magnetic radius differ by $2.7\sigma$, and a simple average yields $r_M= 0.851(26)$ fm. The circumstances under which published muonic hydrogen and electron scattering data could be reconciled are discussed, including a possible deficiency in the standard radiative correction model which requires further analysis.