Abstract
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 (ν¯ee−), 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.
Highlights
Decay of polarized muon at rest is the appropriate process to test the time reversal violation (TRV) and space–time structure of the leptonic charged weak interactions
According to the Standard Model (SM) [1,2,3], the dominant weak interaction responsible for the decay of polarized muons at rest (DPMaR) has a vector-axial (V-A) structure [4], which has been confirmed by precise measurements of the electron observables and of the neutrino energy spectrum
We see that in the case of the transversely polarized antineutrino beam coming from the polarized muon decay, the interference terms between the standard coupling g and exotic g
Summary
Decay of polarized muon at rest is the appropriate process to test the time reversal violation (TRV) and space–time structure of the leptonic charged weak interactions It may be an important source of information on the right-chirality neutrinos. The CP violation is observed only in the decays of neutral K- and B-mesons [9] This situation has led to the appearance of various non-standard schemes, in which the exotic V + A, scalar (S), tensor (T), pseudoscalar (P) couplings of the interacting right-chirality neutrinos and new CP-breaking phases can appear. We mean neutrino observables consisting only of the interference terms between the standard coupling of leftchirality neutrinos and exotic couplings of the right-chirality ones and independent of the neutrino mass These quantities would make it possible to look for the non-standard T-violating phases. Appendix A includes the formulas for the four-vector νe polarization and density operator used in calculations
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