Measurement of double-$\beta$ decay of $^{150}$Nd to the 0$^+_1$ excited state of $^{150}$Sm in NEMO-3

TL;DR

This paper reports the first detection of the two-neutrino double-beta decay of $^{150}$Nd to an excited state in $^{150}$Sm, measuring its half-life and setting limits on other decay modes using NEMO-3 data.

Contribution

The study provides the first experimental evidence for the $^{150}$Nd decay to the 0$^+_1$ excited state, with a precise half-life measurement and new limits on related decay channels.

Findings

First detection of $^{150}$Nd decay to 0$^+_1$ excited state with >5σ significance

Measured half-life of approximately 1.11 x 10^{20} years

Set limits on decay modes to other excited states and neutrinoless decay

Abstract

The NEMO-3 results for the double-$\beta$ decay of $^{150}$Nd to the 0$^+_1$ and 2$^+_1$ excited states of $^{150}$Sm are reported. The data recorded during 5.25 yr with 36.6 g of the isotope $^{150}$Nd are used in the analysis. For the first time, the signal of the $2\nu\beta\beta$ transition to the 0$^+_1$ excited state is detected with a statistical significance exceeding 5$\sigma$. The half-life is measured to be $T_{1/2}^{2\nu\beta\beta}(0^+_1) = \left[ 1.11 ^{+0.19}_{-0.14} \,\left(\mbox{stat}\right) ^{+0.17}_{-0.15}\, \left(\mbox{syst}\right) \right] \times10^{20}\,\mbox{yr}$. The limits are set on the $2\nu\beta\beta$ decay to the 2$^+_1$ level and on the $0\nu\beta\beta$ decay to the 0$^+_1$ and 2$^+_1$ levels of $^{150}$Sm.