New Limit for Neutrinoless Double-Beta Decay of ${}^{100}\mathrm{Mo}$ from the CUPID-Mo Experiment

The CUPID-Mo experiment at the Laboratoire Souterrain de Modane (France) is a demonstrator for CUPID, the next-generation ton-scale bolometric $0\nu \beta \beta$ experiment. It consists of a 4.2 kg array of 20 enriched ${\mathrm{Li}}_2$${}^{100}\mathrm{Mo}{\mathrm{O}}_4$ scintillating bolometers to search for the lepton-number-violating process of $0\nu \beta \beta$ decay in ${}^{100}\mathrm{Mo}$. With more than one year of operation (${}^{100}\mathrm{Mo}$ exposure of $1.17\mathrm{kg}\times \mathrm{yr}$ for physics data), no event in the region of interest and, hence, no evidence for $0\nu \beta \beta$ is observed. We report a new limit on the half-life of $0\nu \beta \beta$ decay in ${}^{100}\mathrm{Mo}$ of $T_{1/2}>1.5\times {10}^{24}\mathrm{yr}$ at 90% C.I. The limit corresponds to an effective Majorana neutrino mass $⟨m_{\beta \beta }⟩<(0.31–0.54)\mathrm{eV}$, dependent on the nuclear matrix element in the light Majorana neutrino exchange interpretation.

Figure 1

Physics spectrum (blue) for $2.16\mathrm{kg}\times \mathrm{yr}$ of data and calibration spectrum (red) scaled to match the 2615 keV counts from ${}^{208}\mathrm{Tl}$. $\mathrm{A}\pm 50\mathrm{keV}$ region around $Q_{\beta \beta }$ has been blinded (gray).

Figure 2

Physics spectrum for $2.16\mathrm{kg}\times \mathrm{yr}$ of data after unblinding. No event is observed in the detector- and dataset-based ROI. A single event, highlighted in cyan, has been observed in the analysis region. In a further refinement of the analysis, it was identified as a $\beta$ candidate out of the ${}^{212}\mathrm{Bi}\to {}^{208}\mathrm{Tl}\to {}^{208}\mathrm{Pb}$ part of the natural decay chain (see the text). For visualization, the exposure-weighted mean ROI for $0\nu \beta \beta$ decay (17.9 keV wide) has been indicated with solid black lines.