Neutrino elastic scattering on polarized electrons as a tool for probing the neutrino nature

Abstract

Possibility of using the polarized electron target (PET) for testing the neutrino nature is considered. One assumes that the incoming electron neutrino (ν e ) beam is the superposition of left chiral states with right chiral ones. Consequently the non-vanishing transversal components of ν e spin polarization may appear, both T-even and T-odd. ν e s are produced by the low energy monochromatic (un)polarized emitter located at a near distance from the hypothetical detector which is able to measure both the azimuthal angle and polar angle of the recoil electrons, and/or also the energy of the outgoing electrons with a high resolution. A detection process is the elastic scattering of ν e s (Dirac or Majorana) on the polarized electrons. Left chiral (LC) ν e s interact mainly by the standard V − A interaction, while right chiral (RC) ones participate only in the non-standard V + A, scalar S R , pseudoscalar P R and tensor T R interactions. We show that a distinction between the Dirac and Majorana ν e s is possible both for the purely left chiral states and the left-right superposition. In the first case a departure from the standard prediction of the azimuthal asymmetry of recoil electrons is caused by the interferences between the non-standard complex S and T couplings, proportional to the angular correlations (T-even and T-odd) among the polarization of the electron target, the incoming neutrino momentum and the outgoing electron momentum. Such a deviation would indicate the Dirac nature of ν e s. In the second variant the azimuthal asymmetry, polar distribution and energy spectrum of scattered electrons are sensitive to the interference terms between the standard and exotic interactions, proportional to the various angular correlations (T-even and T-odd) among the transversal ν e spin polarization (related to the ν e source), the electron target polarization, the incoming ν e momentum and the outgoing electron momentum. The basic difference a between the Dirac and Majorana ν e s arises from the absence of T and V interactions in the Majorana scenario. Moreover, in the Majorana case the above observables contain the non-vanishing interference between V − A and V + A interactions, proportional to the T-even longitudinal ν e polarization. Our model-independent study is carried out for the flavor ν e eigenstates in the relativistic ν e limit.