New measurements of the proton's size and structure using polarized photons

TL;DR

This paper reports on advanced measurements of the proton's size and internal structure using polarized photons, revealing complex quark dynamics and a notable discrepancy in charge radius measurements from different experimental methods.

Contribution

It introduces new experimental techniques with polarized photons that provide deeper insights into the proton's structure and highlights a significant discrepancy in charge radius measurements.

Findings

Proton's structure involves quark orbital angular momentum and relativistic effects.

Charge and magnetization distributions differ from quark spatial distributions.

A discrepancy exists between muonic hydrogen and electron-proton charge radius measurements.

Abstract

Improved measurements of the proton's structure are now possible thanks to significant technical advances that allow us to probe the proton with polarized photons. These measurements have shown that the proton is not as simple as previously believed: quark orbital angular momentum and relativistic effects play an important role and the spatial distribution of charge and magnetization do not simply mimic the spatial distribution of the quarks. Even more recently, the large scale structure and size of the proton have been examined more carefully, and a significant discrepancy has been observed between the charge radius of the proton as measured in the Lamb shift of muonic hydrogen and measurements using the electron-proton interaction.