Measurement of the 2$\nu\beta\beta$ decay half-life of $^{150}$Nd and a search for 0$\nu\beta\beta$ decay processes with the full exposure from the NEMO-3 detector

TL;DR

This study measures the two-neutrino double-beta decay half-life of $^{150}$Nd with high precision and searches for neutrinoless double-beta decay, setting new lower limits on its half-life and constraining neutrino mass.

Contribution

The paper provides the most precise measurement of the $^{150}$Nd two-neutrino double-beta decay half-life and sets new limits on neutrinoless decay mechanisms using the full NEMO-3 dataset.

Findings

Measured $^{150}$Nd two-neutrino double-beta decay half-life as (9.34 ± 0.22 (stat.) +0.62/-0.60 (syst.))×10^{18} y

No evidence found for neutrinoless double-beta decay, setting a lower limit of 2.0×10^{22} y at 90% C.L.

Constrained the effective neutrino mass to less than 1.6 - 5.3 eV.

Abstract

We present results from a search for neutrinoless double-$\beta$ ($0\nu\beta\beta$) decay using 36.6 g of the isotope $^{150}$Nd with data corresponding to a live time of 5.25 y recorded with the NEMO-3 detector. We construct a complete background model for this isotope, including a measurement of the two-neutrino double-$\beta$ decay half-life of $T^{2\nu}_{1/2}=$[9.34 $\pm$ 0.22 (stat.) $^{+0.62}_{-0.60}$ (syst.)]$\times 10^{18}$ y for the ground state transition, which represents the most precise result to date for this isotope. We perform a multivariate analysis to search for \zeronu decays in order to improve the sensitivity and, in the case of observation, disentangle the possible underlying decay mechanisms. As no evidence for \zeronu decay is observed, we derive lower limits on half-lives for several mechanisms involving physics beyond the Standard Model. The observed lower limit, assuming light Majorana neutrino exchange mediates the decay, is $T^{0\nu}_{1/2} >$ 2.0 $\times 10^{22}$ y at the 90% C.L., corresponding to an upper limit on the effective neutrino mass of $\langle m_{\nu} \rangle$ $<$ 1.6 - 5.3 eV..