Status of the determination of the electron–neutrino mass

Abstract

(1) The classical way to determine the electron anti-neutrino mass is the single Beta Decay of Tritium [3H →3He + e−+νec] (Particle Physics Booklet, 2014; Aker et al., 2019). This special decay is favored by the small Q-value Q=18.5737± 0.00025 keV (Aker et al., 2019). Presently KATRIN (Aker et al., 2019) yields an upper limit of 1.1 eV (90% CL) for the neutrino mass the best result. (2) Electron capture of a bound electron [67Ho163+ bound electron → 66Dy163+νe]distributes the Q-value of the decay between the energy (rest-mass plus kinetic energy) of the emitted neutrino and the excitation of the daughter atom. The maximum excitation of the daughter atom is the Q-value minus the neutrino rest mass. Thus the difference of the energies of the Q-value and the upper end of the deexcitation spectrum of the daughter atom is the neutrino mass. (3) The neutrinoless Double Beta Decay requires, that the neutrino is a Majorana particle, thus identical with the anti-particle. A good example is the decay: [3276Ge →3476Se + 2e−]. The signal for the neutrinoless Double Beta decay is the sum of the energies of the two emitted electrons for the 76Ge decay at a value of 2038 keV. The strength of this peak is proportional to the neutrino mass squared. (4) If Cosmology can reliably describe the galaxy formation, the average distances of the galaxies depending on the sum of the masses of the three neutrinos yield a value for the sum of the three masses. Larger neutrino masses favor an early formation of galaxies and thus a larger average distance of the galaxies. Smaller neutrino masses favor due to the pressure of the lighter neutrinos a later formation of galaxies and thus yield a smaller average distance of the galaxies. The present contribution reviews the status of these approaches for the neutrino masses.