Azimuthal asymmetry of recoil electrons in neutrino-electron elastic scattering as signature of neutrino nature

TL;DR

This paper proposes a method to distinguish Dirac from Majorana neutrinos by analyzing azimuthal asymmetries in recoil electrons during neutrino-electron elastic scattering, considering exotic interactions and neutrino polarization.

Contribution

It introduces a novel approach using azimuthal asymmetry measurements to identify neutrino nature, incorporating exotic scalar and tensor interactions in a model-independent framework.

Findings

Azimuthal asymmetry differs for Dirac and Majorana neutrinos due to interference effects.

Interference between standard and exotic couplings depends on neutrino polarization.

Potential to detect CP-violating phases through asymmetry measurements.

Abstract

In this paper, we show how a presence of the exotic scalar, tensor weak interactions in addition to the standard vector-axial (V-A) one may help to distinguish the Dirac from Majorana neutrinos in the elastic scattering of (anti)neutrino beam off the unpolarized electrons in the limit of vanishing (anti)neutrino mass. We assume that the incoming (anti)neutrino beam comes from the polarized muon decay at rest and is the left-right chiral mixture with assigned direction of the transversal spin polarization with respect to the production plane. We display that the azimuthal asymmetry in the angular distribution of recoil electrons is generated by the interference terms between the standard and exotic couplings, which are proportional to the transversal (anti)neutrino spin polarization and independent of the neutrino mass. This asymmetry for the Majorana neutrinos is distinct from the one for the Dirac neutrinos through the absence of interference between the standard and tensor couplings. Additionally, the interference term between the standard and scalar coupling of the only left chiral neutrinos, absent in the Dirac case, appears. We also indicate the possibility of utilizing the azimuthal asymmetry measurements to search for the new CP-violating phases. Our analysis is model-independent and consistent with the current upper limits on the non-standard couplings.