The Proton Elastic Form Factor Ratio at Low Momentum Transfer

TL;DR

This study presents high-precision measurements of the proton elastic form factor ratio at low momentum transfer, revealing it is less than unity and differs from recent models, indicating GEp is smaller than expected.

Contribution

It provides new precise data on the proton form factor ratio at low Q^2, challenging existing phenomenological fits and highlighting deviations from the dipole model.

Findings

Form factor ratio less than unity at low Q^2

Deviation primarily due to smaller GEp values

Data challenges existing phenomenological models

Abstract

High precision measurements of the proton elastic form factor ratio have been made at four-momentum transfers, Q^2, between 0.2 and 0.5 GeV^2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q^2 range the deviation from unity is primarily due to GEp being smaller than the dipole parameterization.