2017/09/27 by R. Gilman, Gilman, R., E. J. Downie +114 · 5 citations
Engineering · Physics and Astronomy · #FOS: Physical sciences #Instrumentation and Detectors (physics.ins-det) #Nuclear Experiment (nucl-ex) #Particle Accelerators and Free-Electron Lasers #Particle accelerators and beam dynamics #Scientific Research and Discoveries
paper · pdf · doi:10.48550/arxiv.1709.09753
openalex publication_date 2017/09/27 · openalex created_date 2017/10/06 · openalex updated_date 2026/07/28
The difference in proton radii measured with μp atoms and with ep atoms and scattering remains an unexplained puzzle. The PSI MUSE proposal is to measure μp and e p 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 μp 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 μp 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 ≈5σ significance, similar to that already established between the regular and muonic hydrogen Lamb shift.