Measurement of the double-beta decay half-life and search for the neutrinoless double-beta decay of ⁴⁸Ca with the NEMO-3 detector

Abstract : The NEMO-3 experiment at the Modane Underground Laboratory investigates the double-beta decay of ⁴⁸Ca. Using 5.25 yr of data recorded with a 6.99 g sample of ⁴⁸Ca, approximately 150 double-beta decay candidate events are selected with a signal-to-background ratio greater than 3. The half-life for the two-neutrino double-beta decay of ⁴⁸Ca is measured to be T₁^{/2 2 ν}=[6. 4_-0.6^+0.7(stat₎^{-0.9 +1.2}(syst ) ]×1 0¹⁹ yr . A search for neutrinoless double-beta decay of ⁴⁸Ca yields a null result, and a corresponding lower limit on the half-life is found to be T₁^{/2 0 ν}>2.0 ×1 0²² yr at 90% confidence level, translating into an upper limit on the effective Majorana neutrino mass of ⟨m_{β β}⟩<6.0 - 26 eV , with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.