The Charge Radius of the Proton

TL;DR

This paper investigates the discrepancy in proton charge radius measurements between muonic hydrogen and regular hydrogen, analyzing experimental data and theoretical models to identify potential sources of error and assumptions.

Contribution

It provides a model-independent analysis of electron-proton scattering data and examines theoretical assumptions in muonic hydrogen calculations.

Findings

Previous scattering data underestimated errors.

Hidden model assumptions in muonic hydrogen calculations identified.

Effective field theory used to analyze proton structure effects.

Abstract

Recently, the charge radius of the proton was extracted for the first time from muonic hydrogen. The value obtained is five standard deviations away from similar measurements of regular hydrogen. This talk discusses work done in collaboration with Richard J. Hill, to address this discrepancy. First, we have studied the extraction of the charge radius of the proton from electron-proton scattering data in a model-independent way. We have shown that previous extractions, spanning a period of over 40 years, have underestimated their errors. Second, we have looked at a model-independent analysis of proton structure effects for hydrogen-like bound states, using the tool of an effective field theory, namely NRQED. We have identified hidden model-dependent assumptions in the theoretical calculation behind the muonic hydrogen result.