Abstract
Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay (2nu beta beta ) half-life of ^{82}Se as T_{smash {1/2}}^{2nu } !=! left[ 9.39 pm 0.17left( text{ stat }right) pm 0.58left( text{ syst }right) right] times 10^{19} y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is left| M^{2nu }right| = 0.0498 pm 0.0016. In addition, a search for neutrinoless double beta decay (0nu beta beta ) 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 T_{1/2}^{0nu } > 2.5 times 10^{23} ,text{ y } ,(90%,text{ C.L. }) for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of langle m_{nu } rangle < left( 1.2{-}3.0right) ,text{ eV }, where the range reflects 0nu beta beta nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other 0nu beta beta mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.
Highlights
The observation of neutrino oscillations has provided proof that the neutrino has non-zero mass [1,2,3]
We present the results of the 82Se 2νββ measurement and 0νββ searches with the full data set collected by the NEMO-3 detector, representing a fivefold increase in exposure compared to the previously published result [24]
We considered four lepton number violating mechanisms for 0νββ: light Majorana neutrino exchange, the admixture of right-handed currents in electroweak interactions, 0νββ
Summary
The observation of neutrino oscillations has provided proof that the neutrino has non-zero mass [1,2,3]. Two-neutrino double beta decay (2νββ) is a rare second order process that is allowed in the Standard Model It has been observed in 12 isotopes with half-lives ranging from 1019 to 1024 y [12,13]. One of the most promising double beta decay (ββ) candidates is 82Se due to its high Q-value (2997.9(3) keV [14]), above most common backgrounds from natural radioactivity, relatively high isotopic abundance (8.83% [15]) and existing robust technologies of isotopic enrichment through centrifugation It has been selected as the isotope of choice for a number of planned 0νββ decay experiments [16,17]. We present the results of the 82Se 2νββ measurement and 0νββ searches with the full data set collected by the NEMO-3 detector, representing a fivefold increase in exposure compared to the previously published result [24]
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