Decay of polarized muon at rest as a source of polarized antineutrino beam

In this Letter, we indicate the possibility of using the decay of polarized muons at rest (DPMaR) as a source of the transversely polarized electron antineutrino beam. Such a beam could be used to probe new effects beyond standard model such as: time reversal violation, existence of right-chirality (anti)neutrinos. The (anti)neutrinos are assumed to be Dirac fermions with non-zero mass. We analyze a scenario with the participation of the complex exotic vector, scalar and tensor couplings of the right-chirality electron antineutrinos in addition to the standard vector coupling of the left-chirality ones. We show that the energy–angle distribution of the electron antineutrinos from the DPMaR depends on the interference terms between standard and exotic couplings, which are proportional to the transverse components of the antineutrino spin polarization and independent of a antineutrino mass. It allows to calculate the flux of electron antineutrinos and the expected number of recoil electrons in the elastic antineutrino–electron scattering $(\bar{\nu }_{e}e^{-})$, where the incoming antineutrino beam comes from the DPMaR and is transversely polarized. Our analysis is model-independent and consistent with the current upper limits on the non-standard couplings. The results are presented in a limit of infinitesimally small mass for all particles produced in the muon decay.