Technical Design Report for the Paul Scherrer Institute Experiment R-12-01.1: Studying the Proton "Radius" Puzzle with μp Elastic Scattering

Abstract

The difference in proton radii measured with $\mu p$ atoms and with $ep$ atoms and scattering remains an unexplained puzzle. The PSI MUSE proposal is to measure $\mu p$ and $ep$ scattering in the same experiment at the same time. The experiment will determine cross sections, two-photon effects, form factors, and radii independently for the two reactions, and will allow $\mu p$ and $ep$ results to be compared with reduced systematic uncertainties. These data should provide the best test of lepton universality in a scattering experiment to date, about an order of magnitude improvement over previous tests. Measuring scattering with both particle polarities will allow a test of two-photon exchange at the sub-percent level, about a factor of four improvement on uncertainties and over an order of magnitude more data points than previous low momentum transfer determinations, and similar to the current generation of higher momentum transfer electron experiments. The experiment has the potential to demonstrate whether the $\mu p$ and $ep$ interactions are consistent or different, and whether any difference results from novel physics or two-photon exchange. The uncertainties are such that if the discrepancy is real it should be confirmed with $\approx$5$\sigma$ significance, similar to that already established between the regular and muonic hydrogen Lamb shift.

Cited by in corpus (17)

• The proton charge radius
• QED at NNLO with McMule
• Proton charge radius extraction from electron scattering data using dispersively improved chiral effective field theory
• An experimental program with high duty-cycle polarized and unpolarized positron beams at Jefferson Lab
• The proton radius (puzzle?) and its relatives
• Operation and characterization of a windowless gas jet target in high-intensity electron beams
• A Liquid Hydrogen Target for the MUSE Experiment at PSI
• Soft-photon corrections to the Bethe-Heitler process in the $\gamma p\to l^{+}{l}^{-}p$ reaction
• Radiative and chiral corrections to elastic lepton-proton scattering in chiral perturbation theory
• Precision Measurement of the Beam-Normal Single-Spin Asymmetry in Forward-Angle Elastic Electron-Proton Scattering
• Characterization of Muon and Electron Beams in the Paul Scherrer Institute PiM1 Channel for the MUSE Experiment
• Elements of QED-NRQED Effective Field Theory: II. Matching of Contact Interactions
• Lepton mass effects for beam-normal single-spin asymmetry in elastic muon-proton scattering
• Ground state hyperfine structure of light muon-electron ions
• Energy interval 3S-1S in muonic hydrogen
• Exact Relations for Two-Photon-Exchange Effect in Elastic $ep$ Scattering by Dispersion Relation and Hadronic Model
• Contribution of hard photon emission to charge asymmetry in elastic (anti)lepton-proton scattering