2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/230745A neutrino mass matrix is considered under conditions of a CP invariance and a small reactor mixing $θ_{13}$ angle. Absolute mass values for three neutrinos are evaluated for normal and inverted hierarchy spectra on the ground of data for oscillation mixing neutrino parameters and an effective neutrino mass $m_{ββ}$ related to a probability of neutrinoless two beta decay.7 pages, added references, corrected style and typos, enlarged the discussion and added a consideration of small values of theta_{13}High Energy Physics - Phenomenologytext