Abstract
In this paper we indicate a possibility of utilizing the elastic scattering of Dirac low-energy (sim 1 MeV) electron neutrinos (nu _es) on a polarized electron target (PET) in testing the time reversal symmetry violation (TRSV). We consider a scenario in which the incoming nu _e beam is a superposition of left chiral (LC) and right chiral (RC) states. LC nu _e interact mainly by the standard V-A and small admixture of non-standard scalar S_L, pseudoscalar P_L, tensor T_L interactions, while RC ones are only detected by the exotic V + A and S_R, P_R, T_R interactions. As a result of the superposition of the two chiralities the transverse components of nu _{e} spin polarization (T-even and T-odd) may appear. We compute the differential cross section as a function of the recoil electron azimuthal angle and scattered electron energy, and show how the interference terms between standard V-A and exotic S_R, P_R, T_R couplings depend on the various angular correlations among the transversal nu _e spin polarization, the polarization of the electron target, the incoming neutrino momentum and the outgoing electron momentum in the limit of relativistic nu _e. We illustrate how the maximal value of recoil electrons azimuthal asymmetry and the asymmetry axis location of outgoing electrons depend on the azimuthal angle of the transversal component of the nu _e spin polarization, both for the time reversal symmetry conservation (TRSC) and TRSV. Next, we display that the electron energy spectrum and polar angle distribution of the recoil electrons are also sensitive to the interference terms between V-A and S_R, P_R, T_R couplings, proportional to the T-even and T-odd angular correlations among the transversal nu _e polarization, the electron polarization of the target, and the incoming nu _e momentum, respectively. We also discuss the possibility of testing the TRSV by observing the azimuthal asymmetry of outgoing electrons, using the PET without the impact of the transversal nu polarization related to the production process. In this scenario the predicted effects depend only on the interferences between S_R and T_R couplings. Our model-independent analysis is carried out for the flavor nu _e. To make such tests feasible, the intense (polarized) artificial nu _e source, PET and the appropriate detector measuring the directionality of the outgoing electrons and/or the recoil electrons energy with a high resolution have to be identified.
Highlights
One of the fundamental problems in neutrino physics is whether the time reversal symmetry violation (TRSV) takes place in purely leptonic processes at low energies [e.g. the neutrino–electron elastic scattering (NEES)]
We have shown that the polarized electron target (PET) may be the useful tool for the detection of the non-standard couplings of right chiral (RC) interacting νes and the effects of TRSV caused by the triple correlations present in the differential cross section for the NEES
According to the standard electro-weak model (SM) prediction the left–right azimuthal asymmetry of the recoil electrons has the maximal value at Φ = π/2 and the location of asymmetry axis is fixed, Figs
Summary
One of the fundamental problems in neutrino physics is whether the TRSV takes place in purely leptonic processes at low energies [e.g. the neutrino–electron elastic scattering (NEES)]. According to the standard electro-weak model (SM) [1,2,3,4,5], the V and A couplings of LC νe may only participate in the NEES and the hermiticity conditions of the interaction lagrangian require the real coupling constants This means that there is no possibility of appearing the TRSV correlations in the differential cross section for the NEES, even when the electron target is polarized. We show in a modelindependent way how the admixture of the exotic S, T, P, V + A complex couplings of RC νes in addition to the standard V, A real couplings of LC ones affects the azimuthal distribution and asymmetry of the recoil electrons, polar distribution of scattered electrons and their energy spectrum, and the possibility of TRSV in the relativistic νe limit. Calculations are carried out with the use of the covariant projectors for the incoming νes (including both the longitudinal and transversal components of the spin polarization)
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