Precision Measurements of the Proton Elastic Form Factor Ratio

TL;DR

This paper presents high-precision polarization measurements of the proton elastic form factor ratio at low Q^2, revealing a small but persistent deviation from unity, which informs understanding of proton structure and two-photon effects.

Contribution

It provides new high-precision polarization data for the proton form factor ratio at low Q^2, extending previous measurements and challenging existing theoretical models.

Findings

Deviation from unity persists at Q^2 < 1 (GeV/c)^2

Data suggest small but significant deviation at low Q^2

Results impact theoretical understanding of two-photon contributions

Abstract

New high precision polarization measurements of the proton elastic form factor ratio in the Q^2 range from 0.3 to 0.7 [GeV/c]^2 have been made. These elastic H(e,e'p) measurements were done in Jefferson Lab's Hall A using 80% longitudinally polarized electrons and recoil polarimetry. For Q^2 greater than 1 [GeV/c]^2, previous polarization data indicated a strong deviation of the form factor ratio from unity which sparked renewed theoretical and experimental interest in how two-photon diagrams have been taken into account. The new high precision data indicate that the deviation from unity, while small, persists even at Q^2 less than 1 [GeV/c]^2.