Neutrinoless Double Beta Decay Rate Research Articles

Estimation of bounds for left-right mixing from nuclear double beta decay processes

Nuclear matrix elements, extracted from a systematic calculation of neutrinoless double beta decay rates for 0 + g.s→o + g.s transitions in 76Ge, 82Se, 128Te, 130Te and 136Xe, have been used to compute bounds on the left-right mixing angle ζ of the weak currents. The parameters of the nuclear model have been fixed by calculating the corresponding two-neutrino double beta decay half lives. The present analysis favours a mixing of the order of |tanξ| < 10 −3 which is to be compared with those obtained in muon decay (|tan ξ| ⩽ 0.035) and in supernova (|tan ξ| ⩽ 10 −5) analysis. It shows that nuclear structure calculations yield estimates on ξ which complement the existing data.

Description of the 0 + → 0 + neutrinoless double-beta decay transition in 76Ge : Particle-number-projected quasiparticle random phase approximation

The 0 + → 0 + neutrinoless double-beta decay rate in 76Ge is calculated in the framework of a particle-number-projected quasiparticle random-phase approximation theory. The Fermi theory of the weak decay is extended in order to include quark degrees of freedom, which are treated in a relativistic quark model with harmonic confinement. The matrix elements which are relevant for the calculation of the half-life are expressed in terms of electron s- and p-wave contributions. Recoil effects arise in the model from the quark recoil in the decaying neutrons. Calculations are performed avoiding closure and starting from the current quark picture thus avoiding the use of effective vector and axial-vector coupling constants. It is found that the particle-number-projected formalism yields results which are similar to the ones obtained with the unprojected model. S- and p-wave effects upon the matrix elements are discussed. An upper limit for the effective Majorana mass of the neutrino, of the order of 3 eV, is deduced from the calculations.

Neutrinoless double beta decay and a new limit on the lepton number violation

We have calculated the neutrinoless double beta decay rate of 76Ge. We take into account for the first time a relativistic correction to the nuclear current including weak magnetism. Its effect is to cancel a considerable part of the decay amplitude and we obtain less stringent upper limits on the neutrino Majorana mass and the right-handed weak leptonic current compared with previous calculations.