The Proton Charge Radius from Dimuon Photoproduction off the Proton

TL;DR

This paper explores the potential of using dimuon photoproduction off protons to measure the proton charge radius, focusing on low momentum transfer regions accessible with high-energy photon beams.

Contribution

It demonstrates the feasibility of extracting proton electromagnetic form factors at very low Q^2 via dimuon photoproduction, offering an alternative method to existing scattering experiments.

Findings

Bethe-Heitler mechanism dominates at small momentum transfers.

Proton charge radius can be extracted from low Q^2 form factors.

Optimal kinematic conditions for measurement are identified.

Abstract

We investigate the feasibility of measuring the proton charge radius through dimuon photoproduction off a proton target. Our findings indicate that the Bethe-Heitler mechanism, which dominates at small momentum transfers, allows for an extraction of the proton electromagnetic form factors in the extremely low $Q^2$ region below $10^{-3}$ GeV$^2$ in the spacelike region, when the incident photon beam energy exceeds several hundred MeV. The optimal kinematical region and a sensitivity study of the proton charge radius from dimuon photoproduction are presented. Such a measurement is expected to provide an alternative to the elastic muon-proton scattering measurements such as MUSE at PSI and AMBER at CERN.