The proton charge radius

Abstract

Nucleons (protons and neutrons) are the building blocks of atomic nuclei, and are responsible for more than 99\% of the visible matter in the universe. Despite decades of efforts in studying its internal structure, there are still a number of puzzles surrounding the proton such as its spin, and charge radius. Accurate knowledge about the proton charge radius is not only essential for understanding how quantum chromodynamics (QCD) works in the non-perturbative region, but also important for bound state quantum electrodynamics (QED) calculations of atomic energy levels. It also has an impact on the Rydberg constant, one of the most precisely measured fundamental constants in nature. This article reviews the latest situation concerning the proton charge radius in light of the new experimental results from both atomic hydrogen spectroscopy and electron scattering measurements, with particular focus on the latter. We also present the related theoretical developments and backgrounds concerning the determination of the proton charge radius using different experimental techniques. We discuss upcoming experiments, and briefly mention the deuteron charge radius puzzle at the end.

49 pages, 28 figures, review prepared for Rev. Mod. Phys

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Cited by in corpus (15)

• The proton structure in and out of muonic hydrogen
• Pion charge radius from pion+electron elastic scattering data
• Hadron and light nucleus radii from electron scattering
• Self-consistent extraction of spectroscopic bounds on light new physics
• Measurement of a helium tune-out frequency: an independent test of quantum electrodynamics
• Probe the color screening in proton-nucleus collisions with complex potentials
• Transverse charge density and the radius of the proton
• Understanding the systematic differences in extractions of the proton electric form factors at low-$Q^2$
• The electromagnetic Sigma-to-Lambda transition form factors with coupled-channel effects in the space-like region
• Elastic Positron-Proton Scattering at Low Q${}^2$
• Investigating saturation effects and the virtual pion in leading neutron events at HERA with the dipole model
• Looking at QED with Dyson-Schwinger equations: basic equations, Ward-Takahashi identities and the two-photon-two-fermion irreducible vertex
• Laser excitation of the 1s-hyperfine transition in muonic hydrogen
• Sub-GeV $U(1{)}_R$ gauge boson to address the proton radius discrepancy
• A reassessment of nuclear effects in muonic deuterium using pionless effective field theory at N3LO