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. All the interactions are of flavour-conserving type (FC). We show that a distinction between the Dirac and the Majorana $ν_e$ s is possible both for the longitudinal and the transversal $ν_e$ polarizations. 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. Such a deviation would indicate the Dirac $ν_e$ nature and the presence of time reversal symmetry violation (TRSV) interactions. In the second case the azimuthal asymmetries, 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. Our model-independent study is carried out for the flavour $ν_e$ eigenstates in the relativistic $ν_e$ limit.