New Parity-Violating Muonic Forces

Understand

The recent discrepancy between proton charge radius measurements extracted from electron-proton versus muon-proton systems is suggestive of a new force that differentiates between lepton species.

• We identify a class of models with gauged right-handed muon number, which contains new vector and scalar force carriers at the 100 MeV scale or lighter, that is consistent with observations.
• Such forces would lead to an enhancement by several orders-of-magnitude of the parity-violating asymmetries in the scattering of low-energy muons on nuclei.
• The relatively large size of such asymmetries, O(10^{-4}), opens up the possibility for new tests of parity violation in neutral currents with existing low-energy muon beams.