Review of experimental and theoretical status of the proton radius puzzle

Abstract

The discrepancy between the measured Lamb shift in muonic hydrogen and expectations from electron-proton scattering and regular hydrogen spectroscopy has become known as the proton radius puzzle, whose most "mundane" resolution requires a $>5\sigma$ shift in the value of the fundamental Rydberg constant. I briefly review the status of spectroscopic and scattering measurements, recent theoretical developments, and implications for fundamental physics.

22 pages, 14 figures, invited plenary talk presented at XII Quark Confinement and the Hadron Spectrum, Thessaloniki, 2016

References in corpus (45)

• Averages of $b$-hadron, $c$-hadron, and $\tau$-lepton properties as of summer 2016
• High-precision determination of the electric and magnetic form factors of the proton
• First Measurement of the Muon Neutrino Charged Current Quasielastic Double Differential Cross Section
• How bright is the proton? A precise determination of the photon parton distribution function
• Measurements of neutrino oscillation in appearance and disappearance channels by the T2K experiment with 6.6E20 protons on target
• Dispersion analysis of the nucleon form factors including meson continua
• Model independent extraction of the proton charge radius from electron scattering
• Extreme ultraviolet frequency comb metrology
• Two-Photon Physics in Hadronic Processes
• Vector and Axial Nucleon Form Factors:A Duality Constrained Parameterization
• Measurement of Neutrino-Induced Charged-Current Charged Pion Production Cross Sections on Mineral Oil at E${}_{\nu }\sim 1\text{GeV}$
• Muonic hydrogen and MeV forces
• Differences in Quasi-Elastic Cross-Sections of Muon and Electron Neutrinos
• New Parity-Violating Muonic Forces
• Theoretical Constraints and Systematic Effects in the Determination of the Proton Form Factors
• Proton polarisability contribution to the Lamb shift in muonic hydrogen at fourth order in chiral perturbation theory
• Proton size anomaly
• Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering: Determined by the OLYMPUS Experiment
• On the pi pi continuum in the nucleon form factors and the proton radius puzzle
• Model independent extraction of the proton magnetic radius from electron scattering
• The NRQED lagrangian at order 1/M^4
• Strange and charm quark contributions to the anomalous magnetic moment of the muon
• Measurement of Muon Capture on the Proton to 1% Precision and Determination of the Pseudoscalar Coupling g_P
• The two-photon exchange contribution to muonic hydrogen from chiral perturbation theory
• Reduction of the proton radius discrepancy by 3 sigma
• Forward virtual Compton scattering and the Lamb shift in chiral perturbation theory
• First measurement of proton's charge form factor at very low $Q^2$ with initial state radiation
• Fundamental constants and tests of theory in Rydberg states of hydrogen-like ions
• Improved estimates of the nuclear structure corrections in $\mu$D
• Nuclear structure effects in light muonic atoms
• Proton root-mean-square radii and electron scattering
• Proton radius from electron-proton scattering and chiral perturbation theory
• Polynomial fits and the proton radius puzzle
• Constraints on the form factors for K --> pi l nu and implications for V_us
• Lattice Calculation of Nucleon Isovector Axial Charge with Improved Currents
• Two-photon exchange correction to $2S$-$2P$ splitting in muonic helium-3 ions
• Point-Particle Effective Field Theory I: Classical Renormalization and the Inverse-Square Potential
• Two-photon exchange corrections to elastic $e^{-}$-proton scattering: Full dispersive treatment of $\pi N$ states at low momentum transfers
• Point-Particle Effective Field Theory II: Relativistic Effects and Coulomb/Inverse-Square Competition
• Proton rms-radii from low-q power expansions?
• Novel applications of Lattice QCD: Parton distribution functions, proton charge radius and neutron electric dipole moment
• Evaluation of the proton charge radius from e-p scattering
• The Proton Radius Problem and Point-Particle Effective Field Theory
• Calculation of the Nucleon Axial Form Factor Using Staggered Lattice QCD
• Nucleon form factors and couplings with $N_{\mathrm{f}}=2+1$ Wilson fermions

Cited by in corpus (24)

• Search for New Physics with Atoms and Molecules
• Proton and neutron electromagnetic form factors and uncertainties
• Nucleon Axial Radius and Muonic Hydrogen - A New Analysis and Review
• Hadrons and Nuclei
• Parameterization and applications of the low-$Q^2$ nucleon vector form factors
• Lattice QCD and the anomalous magnetic moment of the muon
• Hilbert Series and Operator Basis for NRQED and NRQCD/HQET
• Two-photon exchange correction to the Lamb shift and hyperfine splitting of S levels
• Two-photon exchange contribution to elastic $e^{-}$-proton scattering: Full dispersive treatment of $\pi N$ states and comparison with data
• Robust extraction of proton charge radius from electron-proton scattering data
• Dispersion Theory in Electromagnetic Interactions
• Measuring the Rydberg Constant Using Circular Rydberg Atoms in an Intensity-Modulated Optical Lattice
• Theory of the n=2 levels in muonic helium-3 ions
• Measurement of a helium tune-out frequency: an independent test of quantum electrodynamics
• Sea Quarks Contribution to the Nucleon Magnetic Moment and Charge Radius at the Physical Point
• Advanced extraction of the deuteron charge radius from electron-deuteron scattering data
• Model independent radiative corrections to elastic deuteron-electron scattering
• Radiative corrections to elastic proton-electron scattering measured in coincidence
• Dilepton photoproduction on a deuteron target
• The proton radius puzzle
• Lowest-order QED radiative corrections in unpolarized elastic electron-deuteron scattering beyond the ultra-relativistic limit for the proposed deuteron charge radius measurement at Jefferson Laboratory
• Connecting spatial moments and momentum densities
• Energy interval 3S-1S in muonic hydrogen
• Clustering in hadrons and light nuclei from Lorentz boosted form factors