Final results on ⁸2 Se double beta decay to the ground state of ⁸2 Kr from the NEMO-3 experiment

Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay ( 2ν β β ) half-life of ⁸² Se as T_ 1/22ν \!=\! [ 9.39 ± 0.17( stat ) ± 0.58( syst ) ] × 10¹⁹ y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is | M2ν| = 0.0498 ± 0.0016 . In addition, a search for neutrinoless double beta decay ( 0ν β β ) using 0.93 kg of ⁸² Se observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of T1/20ν > 2.5 × 10²³ \, y \,(90%\, C.L. ) for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of mν < ( 1.2-3.0) \, eV , where the range reflects 0ν β β nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other 0ν β β mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.