Reanalysis of ep Elastic Scattering Data in Terms of Proton Electromagnetic Formfactors

TL;DR

This paper compares three models of proton electromagnetic form factors using extensive elastic scattering data, incorporating novel effects like pionium, and provides refined estimates of the proton charge radius consistent with recent measurements.

Contribution

It introduces an effective two-pion intermediate Coulombic bound state into the generalized vector meson dominance model for the first time and compares multiple parametrizations with a large data set.

Findings

Proton charge radius estimated at 0.897 fm with small uncertainties.

Models with pionium inclusion fit data better and align with recent Lamb shift results.

Comparison shows polynomial fits are less accurate than physically motivated models.

Abstract

We have made the comparison of three parametrizations of the proton electromagnetic form factors in the space-like region using the largest data set on $e^{\pm} p$ elastic scattering ever used. All models have a correct analytical structure with a minimal set of well known singularities. For the first time an effective two-pion intermediate coulombic bound state (pionium) was included into GVMD for nucleon formfactors. For the proton charge radius an estimate derived from our best fits is as follows: r_E^p [\rm fm] = 0.897 \pm 0.002(exp) \pm 0.001(norm) \pm 0.003(models). The traditional ``model independent'' fit by quadratic polynomial gives, in our estimation technology, a much cruder estimate r^p_{E,polinomial} [\rm fm] = 0.887 \pm 0.006(exp) \pm 0.096(norm). Both estimates are closer to the value estimated from the recent hydrogen Lamb shift measurements.