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

Abstract

AbstractPossibility of using the polarized electron target (PET) for testing the neutrino nature is considered. It is assumed that the incoming $$\nu _e$$νe beam is the superposition of left chiral (LC) states with right chiral (RC) ones. Consequently the non-vanishing transversal components of $$\nu _e$$νe spin polarization may appear, both T-even and T-odd. $$\nu _e$$νes 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 the 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 $$\nu _e$$νes (Dirac or Majorana) on the polarized electrons. LC $$\nu _e$$νes interact mainly by the standard $$V - A$$V-A interaction, while RC ones participate only in the non-standard $$V + A$$V+A, scalar $$S_R$$SR, pseudoscalar $$P_R$$PR and tensor $$T_R$$TR interactions. All the interactions are of flavour-conserving type (FC). We show that a distinction between the Dirac and the Majorana $$\nu _e$$νes is possible both for the longitudinal and the transversal $$\nu _e$$νe 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, 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. It is shown that such a deviation would indicate the Dirac $$\nu _e$$νe nature and the presence of time reversal symmetry violation interactions. It is remarkable that the result is conclusive for all Majorana non-standard couplings. 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 among the transversal $$\nu _e$$νe spin polarization, the electron target polarization, the incoming $$\nu _e$$νe momentum and the outgoing electron momentum. In the particular case of the V–A and S couplings the precise measurement of some observables, e.g. the spectrum, can distinguish between the Dirac and the Majorana $$\nu _e$$νes as long as the incoming $$\nu _e$$νe beam has non-vanishing transversal polarization. Our model-independent study is carried out for the flavour $$\nu _e$$νe eigenstates in the relativistic $$\nu _e$$νe limit.