Electromagnetic Form Factors and the Proton Radius Puzzle: A Critical Review of Extraction Methods via Electron-Proton Scattering

TL;DR

This review critically examines methods for extracting proton electromagnetic form factors from electron-proton scattering, highlighting progress, challenges, and the ongoing proton radius puzzle.

Contribution

It provides a comprehensive analysis of various extraction techniques, their evolution, and the systematic uncertainties affecting proton radius measurements.

Findings

Polarization transfer offers more precise form factor ratios at high momentum transfer.

Rosenbluth method yields a larger proton radius (~0.8 fm) compared to polarization transfer results.

Discrepancies in proton radius measurements remain unresolved, requiring further systematic uncertainty reduction.

Abstract

The study of protons, fundamental constituents of atomic nuclei, is crucial for understanding nuclear physics and fundamental forces. This review examines advancements in extracting electromagnetic form factors, essential for probing proton structure. Electron-proton scattering experiments, particularly at Jefferson Lab (JLab) and Mainz Microtron (MAMI), have played a key role [arXiv:2009.10510, arXiv:1912.03881]. Various methodologies, such as Rosenbluth separation and polarization transfer, are discussed, highlighting their evolution and challenges, including systematic uncertainties and theoretical ambiguities [arXiv:1706.00696]. Literature indicates the Rosenbluth method yields a proton radius of approximately 0.8 fm, consistent with early measurements but differing from recent polarization transfer results, which suggest a smaller radius [arXiv:1912.03881]. The polarization transfer technique has become a preferred approach, offering precise measurements of the electric-to-magnetic form factor ratio, especially at high momentum transfer [arXiv:1706.00696, arXiv:1912.03881]. Alternative methods, such as cross-section ratios, extend form factor studies but still face residual uncertainties [arXiv:2009.10510]. While significant progress has been made, discrepancies persist, particularly in proton radius extraction. Future research must address systematic uncertainties to refine our understanding of proton electromagnetic properties and advance particle physics [arXiv:1912.03881, arXiv:1706.00696].