NEUTRINOLESS DOUBLE EC AND RARE BETA DECAYS AS TOOLS TO SEARCH FOR THE NEUTRINO MASS

摘要

Neutrinoless double electron capture (OvECEC) of atomic nuclei has recently attracted a lot of attention due to its potential in accessing the absolute mass scale of the neutrino. In particular, the resonant OvECEC is interesting based on the possible huge enhancement of the corresponding decay rate by a resonance condition. Recently the mass differences of two atom pairs were measured in order to study the enhancement of the OvECEC rates of ~(74)Se and ~(112)Sn. We have evaluated the associated nuclear matrix elements by using the proton-neutron quasiparticle random-phase approximation with realistic two-body interactions. The absolute mass scale of the neutrino can also be accessed through beta decays of small decay energy. Related to this we have also studied the recently discovered rare ultra-low-Q-value beta-decay branch of ~(115)In by using microscopic phonon-quasiparticle coupling schemes. Our calculations suggest that the effects of atomic origin may introduce non-negligible, even dramatic effects on this and other decays with a Q value in this extreme regime of only hundreds of eV.