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

Abstract

The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-${\hat{I}}^2$ decay of ${}^{48}\mathrm{Ca}$. Using $5.25$ yr of data recorded with a $6.99\mathrm{g}$ sample of ${}^{48}\mathrm{Ca}$, approximately $150$ double-${\hat{I}}^2$ decay candidate events have been selected with a signal-to-background ratio greater than $3$. The half-life for the two-neutrino double-${\hat{I}}^2$ decay of ${}^{48}\mathrm{Ca}$ has been measured to be $T_{1/2}^{2\hat{I}½}=[6.4{}_{-0.6}^{+0.7}(stat.){}_{-0.9}^{+1.2}(syst.)]\times 10^{19}\mathrm{yr}$. A search for neutrinoless double-${\hat{I}}^2$ decay of ${}^{48}\mathrm{Ca}$ yields a null result and a corresponding lower limit on the half-life is found to be $T_{1/2}^{0\hat{I}½}>2.0\times 10^{22}\mathrm{yr}$ at $90\%$ confidence level, translating into an upper limit on the effective Majorana neutrino mass of $<m_{{\hat{I}}^2{\hat{I}}^2}><6.0-26$ $\mathrm{eV}$, with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.

8 pages, 5 figures, 3 tables. Final journal version after peer review