6533b860fe1ef96bd12c30cb

RESEARCH PRODUCT

Double-Beta-Decay Matrix Elements And The Effective Value Of Weak Axial Coupling

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description

The neutrinoless double beta (0νββ) decay of atomic nuclei is a possible way to access the nature and mass of the neutrino. These unknown features of the neutrino can be tackled by the 0νββ-decay experiments. In a simplistic picture the rate of 0νββ decay depends on the second power of the double Gamow-Teller nuclear matrix element, M(0ν)GTGT, containing virtual transitions through various multipole states Jπ of the intermediate nucleus. The matrix element is multiplied by the second power of the effective (quenched) value, geffA, of the weak axial-vector coupling gA. The coupling geffA plays an extremely important role in determining the 0νββ-decay rate since the rate is proportional to its 4th power. The quenching issue has become very important in the neutrino-physics community due to its impact on the sensitivities of the present and future large-scale 0νββ-decay experiments. The effective value of gA can be studied in single beta decays of various kinds, as also in the nuclear muon capture. In these cases geffA determines the beta-decay half-lives and spectrum shapes of the emitted electrons/positrons. It also determines the muon-capture rates together with the (effective) induced pseudoscalar coupling. The effective value of the axial coupling can have a strong impact on the beta-spectrum shapes, on 0νββ-decay rates and, e.g., the analysis of the reactor-antineutrino anomaly.