New Physics and the Proton Radius Problem

Abstract

Background: The recent disagreement between the proton charge radius extracted from Lamb shift measurements of muonic and electronic hydrogen invites speculation that new physics may be to blame. Several proposals have been made for new particles that account for both the Lamb shift and the muon anomalous moment discrepancies. Purpose: We explore the possibility that new particles' couplings to the muon can be fine-tuned to account for all experimental constraints. Method: We consider two fine-tuned models, the first involving new particles with scalar and pseudoscalar couplings, and the second involving new particles with vector and axial couplings. The couplings are constrained by the Lamb shift and muon magnetic moments measurements while mass constraints are obtained by kaon decay rate data. Results: For the scalar-pseudoscalar model, masses between 100 to 200 MeV are not allowed. For the vector model, masses below about 200 MeV are not allowed. The strength of the couplings for both models approach that of electrodynamics for particle masses of about 2 GeV. Conclusions: New physics with fine tuned couplings may be entertained as a possible explanation for the Lamb shift discrepancy.

6 pages, 6 figures, v2 contains revised comment on competing model of Lamb Shift discrepancy

References in corpus (6)

• High-precision determination of the electric and magnetic form factors of the proton
• Status of the Fermilab Muon (g-2) Experiment
• Muonic hydrogen and MeV forces
• New Parity-Violating Muonic Forces
• Proton size anomaly
• Spectroscopy as a test of Coulomb's law - A probe of the hidden sector

Cited by in corpus (46)

• Muonic hydrogen and the proton radius puzzle
• Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
• Theory of the 2S-2P Lamb shift and 2S hyperfine splitting in muonic hydrogen
• On the pi pi continuum in the nucleon form factors and the proton radius puzzle
• Probing Muonic Forces and Dark Matter at Kaon Factories
• Model independent extraction of the proton magnetic radius from electron scattering
• Are Electron Scattering Data Consistent with a Small Proton Radius?
• Constraints on muon-specific dark forces
• Nuclear structure contribution to the Lamb shift in muonic deuterium
• Review of experimental and theoretical status of the proton radius puzzle
• Implication of the hidden sub-GeV bosons for the $(g-2{)}_{\mu }$, ${}^8$Be-${}^4$He anomaly, proton charge radius, EDM of fermions and dark axion portal
• Resolving the $(g-2{)}_{\mu }$ and $B$ anomalies with leptoquarks and a dark Higgs boson
• Two-photon exchange correction to $2S$-$2P$ splitting in muonic helium-3 ions
• Constraints on $L_{\mu }-L_{\tau }$ Gauge Interactions from Rare Kaon Decay
• The next generation of laser spectroscopy experiments using light muonic atoms
• Solutions to the MiniBooNE Anomaly from New Physics in Charged Meson Decays
• Constraints to new physics models for the proton charge radius puzzle from the decay $K^{+}\to {\mu }^{+}+\nu +e^{-}+e^{+}$
• Beam normal spin asymmetry for the $ep\to e\Delta (1232)$ process
• Is the proton radius puzzle evidence of extra dimensions?
• New Laboratory Constraints on Neutrinophilic Mediators
• Lepton universality test in the photoproduction of $e^{-}{e}^{+}$ versus ${\mu }^{-}{\mu }^{+}$ pairs on a proton target
• Eta Decay and Muonic Puzzles
• Muonic bound systems, virtual particles and proton radius
• Can Galileons solve the muon problem?
• Leading order corrections to the Bethe-Heitler process in the $\gamma p\to l^{+}{l}^{-}p$ reaction
• Some consequences of the Majoron being the dark radiation
• Extending theories on muon-specific interactions
• Soft-photon corrections to the Bethe-Heitler process in the $\gamma p\to l^{+}{l}^{-}p$ reaction
• Constraints on the Dark Photon Parameter Space from Leptonic Rare Kaon Decays
• Radiative and chiral corrections to elastic lepton-proton scattering in chiral perturbation theory
• Restrained Dark $U(1{)}_d$ at Low Energies
• Polarization observables in lepton-deuteron elastic scattering including the lepton mass
• Hadronic Vacuum Polarization in True Muonium
• Reduced Theoretical Error for QED Tests with 4He+ Spectroscopy
• New Determination of Muonium-Deuterium 1S-2S Isotope Shift
• Polarized Lepton-Nucleon Elastic Scattering and a Search for a Light Scalar Boson
• Hyperfine structure of excited state of muonic helium atom
• New physics via pion capture and simple nuclear reactions
• Dark Matter as a Solution to Muonic Puzzles
• The Stark Effect with Minimum Length
• The LHC as a TeV Muon Beam Dump: Muonphilic Scalars at FASER
• Search for Light Neutral Bosons in the TREK/E36 Experiment at J-PARC
• Implications of recent ${\left(g-2\right)}_{\mu }$ measurements for MeV-GeV dark sector searches
• Sub-GeV $U(1{)}_R$ gauge boson to address the proton radius discrepancy
• Proton Charge Radius and Precision Tests of QED
• Monophotons from Scalar Portal Dark Matter at Neutrino Experiments