On possibility of time reversal symmetry violation in neutrino elastic scattering on polarized electron target

Abstract

In this paper, we indicate a possibility of utilizing the elastic scattering of the Dirac low energy (∼ 1 MeV) electron neutrinos (ν e 's) on the polarized electron target (PET) in testing the time reversal symmetry violation (TRSV). We consider a scenario in which the incoming ν e beam is the superposition of left chiral (LC) and right chiral (RC) states. LC ν e 's 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. In addition, one assumes that the spin polarization vector of the initial ν e 's is turned aside from its momentum, and due to this the nonvanishing transversal component of the ν e spin polarization appears. 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 ν e spin polarization, the polarization of the electron target, the incoming neutrino momentum and the outgoing electron momentum in the limit of relativistic ν 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 ν 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 ν e polarization, the electron polarization of the target, and the incoming ν e momentum, respectively. Our modelindependent analysis is carried out for the flavor ν e 's. To a make such tests feasible, the intense (polarized) artificial ν 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.

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

“…| ην • q| = |1 − 2Q ν L |, where Q ν L is the probability of producing the LC ν e . We see that the interference terms between standard V − A and exotic S R , P R couplings depend on the transversal ν e spin polarization related to the production process (similar regularity as in the Dirac case [21]).…”

“…It is worth reminding that the PET has been proposed to test the flavor composition of (anti)neutrino beam [20] and various effects of non-standard physics. We mean the neutrino magnetic moments, TRSV in the leptonic processes [21], axions, spin-spin interaction in gravitation [22][23][24][25][26][27][28] The possibility of using polarized targets of nucleons and of electrons for the fermionic, scalar and vector dark matter detection is also worth noticing [29][30][31]. The methods of producing the spin-polarized gasses such as helium, argon and xenon are described in [32,33].…”

“…We utilize the experimental values of standard couplings: c L V = 1 + (−0.04 ± 0.015), c L A = 1 + (−0.507 ± 0.014) to evaluate the predicted effects [84]. The laboratory differential cross sections (see Appendix 1 for the Majorana ν e s and [21] for the Dirac case) are calculated with the use of the covariant projectors for the incoming ν e s (including both the longitudinal and transversal components of the spin polarization) in the relativistic limit and for the polarized targetelectrons, respectively [85].…”

Tests of discrete symmetries

“…In practice one can consider the transverse polarization of particles in (non-collinear, two-body) scattering experiments or, conversely, the scattering distribution for polarized particles; since scattering experiments are usually performed with particles interacting mainly through strong or electromagnetic interactions, this restricts the above tests to such interactions, while at the same time introducing the possibility of large spurious effects, thus limiting their potential reach. T tests involving the elastic scattering of electron neutrinos on a polarized electron target have been proposed [81]: by measuring the angular distribution of electrons scattered by an intense ∼ 1 MeV neutrino radioactive source decaying by electron capture, such experiments might be sensitive to T -violating effects beyond the SM, but significant technical developments are required to realize them.…”