Abstract
The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double-beta (0 nu beta beta) decay. We report the final results of a search for 0 nu beta beta decays with 6.914 kg of Mo-100 using the entire NEMO-3 data set with a detector live time of 4.96 yr, which corresponds to an exposure of 34.3 kg . yr.
We perform a detailed study of the expected background in the 0 nu beta beta signal region and find no evidence of 0 nu beta beta decays in the data. The level of observed background in the 0 nu beta beta signal region [2.8-3.2] MeV is 0.44 +/- 0.13 counts/yr/kg, and no events are observed in the interval [3.2-10] MeV.
We therefore derive a lower limit on the half-life of 0 nu beta beta decays in Mo-100 of T-1/2(0 nu beta beta) > 1.1 x 10(24) yr at the 90% confidence level, under the hypothesis of decay kinematics similar to that for light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range < 0.33-0.62 eV.
We also report constraints on other lepton-number violating mechanisms for 0 nu beta beta decays.