Muonic hydrogen and the proton radius puzzle

TL;DR

The paper discusses the proton radius puzzle, highlighting the discrepancy between measurements from muonic hydrogen and electronic methods, and explores potential solutions and future research directions.

Contribution

It provides a comprehensive overview of the proton radius puzzle, analyzing its significance, possible explanations, and outlining future research needed to resolve it.

Findings

Significant discrepancy between muonic and electronic measurements of proton radius

Identification of potential solutions to the proton radius puzzle

Discussion of future experimental and theoretical work needed

Abstract

The extremely precise extraction of the proton radius by Pohl et al. from the measured energy difference between the 2P and 2S states of muonic hydrogen disagrees significantly with that extracted from electronic hydrogen or elastic electron-proton scattering. This is the proton radius puzzle. The origins of the puzzle and the reasons for believing it to be very significant are explained. Various possible solutions of the puzzle are identified, and future work needed to resolve the puzzle is discussed.