Characterization of muon and electron beams in the Paul Scherrer Institute PiM1 channel for the MUSE experiment

Abstract

The MUon Scattering Experiment, MUSE, at the Paul Scherrer Institute, Switzerland, investigates the proton charge radius puzzle, lepton universality, and two-photon exchange, via simultaneous measurements of elastic muon-proton and electron-proton scattering. The experiment uses the PiM1 secondary beam channel, which was designed for high precision pion scattering measurements. We review the properties of the beam line established for pions. We discuss the production processes that generate the electron and muon beams, and the simulations of these processes. Simulations of the π/μ/e beams through the channel using TURTLE and G4beamline are compared. The G4beamline simulation is then compared to several experimental measurements of the channel, including the momentum dispersion at the intermediate focal plane and target, the shape of the beam spot at the target, and timing measurements that allow the beam momenta to be determined. We conclude that the PiM1 channel can be used for high precision π , μ, and e scattering.

The MUon Scattering Experiment (MUSE) at the Paul Scherrer Institute

“…However, MUSE will be most sensitive in the determination of potential differences between the extracted 𝜇 and 𝑒 radii with 𝜎(𝑟 𝑒 − 𝑟 𝜇 ) ≈ 0.005 fm. Any observed differences in the 𝜇𝑝 and 𝑒 𝑝 cross-sections may hint at issues with the radiative corrections or new physics [15].…”

“…The primary proton beam interacts with the carbon M target, and the secondary particles (electrons, muons, and pions) are momentum-selected and transported to the experimental setup. The MUSE collaboration has performed dedicated measurements to characterize the beamline for MUSE [15]. The incident mixed particles are identified and tracked to a liquid hydrogen target.…”