Measurement of the Double Beta Decay Half-life of 150-Nd and Search for Neutrinoless Decay Modes with the NEMO-3 Detector

Abstract

The half-life for double beta decay of 150 Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of 150 Nd the half-life for 2νββ decay is measured to be T 2ν 1/2 = (9.11 +0.25 −0.22 (stat.) ± 0.63 (syst.)) × 10 18 years. The observed limit on the half-life for neutrinoless double beta decay is found to be T 0ν 1/2 > 1.8×10 22 years at 90% Confidence Level. This translates into a limit on the effective Majorana neutrino mass of mν < 4.0 − 6.3 eV if the nuclear deformation is taken into account. We also set limits on models involving Majoron emission, right-handed currents and transitions to excited states.

Neutrinoless quadruple beta decay

“…Coincidentally, it also has a high Q 0ν2β -value, which makes it a popular isotope to test for 0ν2β, with some existing and planned experiments [1]. Once again, NEMO might already be able to constrain 150 Nd 2.079 − −− → 150 Gd with their data [10].…”

“…This may be a too conservative approach, because fourneutrino interactions do not suffer from such stringent constraints as other four-fermion interactions [13]. The effective LNV operator (ν L ν c L ) 2 /Λ discussed here has not been constrained so far, and the contribution to the well-measured invisible Z-width via Z → 4ν only gives Λ > 1/(O (10) √ G F ) ∼ 20 GeV. This, of course, only holds if the mediator is heavy enough to be integrated out in the first place.…”

On the quantitative impact of the Schechter-Valle theorem

“…At the moment, the most promising attempts to find lepton number violation are the experiments searching for neutrinoless double beta decay (0νββ). Several such experiments have been performed (IGEX [4], Heidelberg-Moscow [5], CUORICINO [6], NEMO [7], and others), so far without unambiguous detection. New second generation experiments like GERDA [8], which has been built and is being readied for data taking, will soon improve the sensitivity and may observe 0νββ.…”

Preliminary measurement of the 2$νββ$ decay half-life of $^{150}$Nd to $^{150}$Sm

“…))×10 18 yrs is obtained with a signal to background ratio 2.88. This is a factor of 1.3 improvement on the statistical error compared to the previously published value for 150 Nd which only used half of the total NEMO-3 exposure [4].…”