Neutrinoless double beta decay: Electron angular correlation as a probe of new physics

The angular distribution of the final electrons in the so-called long range mechanism of the neutrinoless double beta decay ($0\nu2\beta$) is derived for the general Lorentz invariant effective Lagrangian. Possible theories beyond the SM are classified from their effects on the angular distribution, which could be used to discriminate among various particle physics models inducing $0\nu2\beta$ decays. However, additional input on the effective couplings will be required to single out the light Majorana-neutrino mechanism. Alternatively, measurements of the effective neutrino mass and angular distribution in $0\nu2\beta$ decays can be used to put independent bounds on the parameters of the underlying physics models. This is illustrated for the mass of the right-handed $W_R$ boson of the left-right symmetric model for assumed values of the angular correlation coefficient and either the effective Majorana neutrino mass $$ or the half-life of the decay