The Radius of the Proton: Size Does Matter

TL;DR

This paper examines the discrepancy in the proton's charge radius as measured through muonic hydrogen spectroscopy, questioning the perturbation theory methods used in the original analysis.

Contribution

It provides a detailed bound-state QED analysis of the muonic hydrogen spectrum to assess the validity of previous perturbation-based conclusions about the proton radius.

Findings

Re-evaluation of the muonic hydrogen spectrum using bound-state QED.

Discussion on the reliability of perturbation theory in this context.

Insights into the proton radius discrepancy and potential sources of error.

Abstract

The measurement by Pohl et al. [1] of the 2S_1/2^F=1 to 2P_3/2^F=2 transition in muonic hydrogen and the subsequent analysis has led to a conclusion that the rms charge radius of the proton differs from the accepted (CODATA [2]) value by approximately 4%, leading to a 4.9 s.d. discrepancy. We investigate the muonic hydrogen spectrum relevant to this transition using bound-state QED with Dirac wave-functions and comment on the extent to which the perturbation-theory analysis which leads to the above conclusion can be confirmed.