Measurement of the double-beta decay half-life and search for the neutrinoless double-beta decay of $^{48}{\rm Ca}$ with the NEMO-3 detector

TL;DR

This study measures the half-life of double-beta decay in $^{48}$Ca and searches for neutrinoless decay modes, providing new experimental limits and insights into neutrino properties using the NEMO-3 detector over 5.25 years.

Contribution

The paper presents the first precise measurement of the two-neutrino double-beta decay half-life of $^{48}$Ca and sets new limits on neutrinoless decay, improving constraints on neutrino mass models.

Findings

Measured $^{48}$Ca$\beta\beta$ half-life as $6.4^{+0.7}_{-0.6} \times 10^{19}$ years.

No evidence found for neutrinoless double-beta decay, setting a lower half-life limit of $2.0 \times 10^{22}$ years.

Established upper bounds on effective Majorana neutrino mass and other exotic decay modes.

Abstract

The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-$\beta$ decay of $^{48}{\rm Ca}$. Using $5.25$ yr of data recorded with a $6.99\,{\rm g}$ sample of $^{48}{\rm Ca}$, approximately $150$ double-$\beta$ decay candidate events have been selected with a signal-to-background ratio greater than $3$. The half-life for the two-neutrino double-$\beta$ decay of $^{48}{\rm Ca}$ has been measured to be $T^{2\nu}_{1/2}\,=\,[6.4\, ^{+0.7}_{-0.6}{\rm (stat.)} \, ^{+1.2}_{-0.9}{\rm (syst.)}] \times 10^{19}\,{\rm yr}$. A search for neutrinoless double-$\beta$ decay of $^{48}{\rm Ca}$ yields a null result and a corresponding lower limit on the half-life is found to be $T^{0\nu}_{1/2} > 2.0 \times 10^{22}\,{\rm yr}$ at $90\%$ confidence level, translating into an upper limit on the effective Majorana neutrino mass of $< m_{\beta\beta} > < 6.0 - 26$ ${\rm eV}$, with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.