Extraction of the mass neutrino from angular asymmetry of electrons β-decay
The mass of electron antineutrinos in laboratory experiments is extracted from the analysis of the energy spectrum of electrons emitted during the beta decay of nuclei and nucleons. Since the total probability of the electron emission is proportional to the square of the matrix element of nucleons and nuclei, the effect of their internal structure on a very small amount of antineutrino mass (1 eV or less) turns out to be significant. This effect can be minimized by measuring the relative characteristics (particle polarizations, angular asymmetries) in pure Fermi and pure gam-Teller transitions. In this case, the full matrix elements are factorized (represented as a product of lepton and nucleon scalar functions, but not tensors), which leads to a reduction of poorly known nucleon structure functions in the numerator and denominator of all formulas for the degrees of polarizations and coefficients of lepton asymmetries.