Solar neutrino interactions with the double-$\beta$ decay nuclei ${}^{82}\mathrm{Se}, {}^{100}\mathrm{Mo}$, and ${}^{150}\mathrm{Nd}$

Solar neutrinos interact within double-beta decay ($\beta \beta$) detectors and contribute to backgrounds for $\beta \beta$ experiments. Background contributions due to solar neutrino interactions with $\beta \beta$ nuclei of ${}^{82}\mathrm{Se}, {}^{100}\mathrm{Mo}$, and ${}^{150}\mathrm{Nd}$ are evaluated. They are shown to be significant for future high-sensitivity $\beta \beta$ experiments that may search for Majorana neutrino masses in the inverted-hierarchy mass region. The impact of solar neutrino backgrounds and their reduction are discussed for future $\beta \beta$ experiments.

Figure 1

Schematic diagrams of the $\beta \beta$ of ${}^{Z-1}A$ to ${}^{Z+1}A$, the solar-$\nu$ CC interaction on ${}^{Z-1}A$ and the electron ($\gamma$) decay to ${}^{Z}A$, and the single $\beta /\gamma$ decays of ${}^{Z}A$ to ${}^{Z+1}A$. $Q_{\beta \beta },Q_{\beta },Q_{\nu }$, and $Q_e$ are the $Q$ values for $\beta \beta ,\beta ,\nu$ CC, and electron capture (EC), respectively.

Figure 2

Solar-$\nu$ capture rates in units of SNU for current $\beta \beta$ nuclei are plotted against the neutrino CC $Q_{\nu }$ value for the lowest $1^{+}$ state. $S_t$ is the total capture rate. Group A nuclei have a large $S_t$. Group B nuclei have a small $S_t$.

Figure 3

The sum spectrum of $\beta$ and $\gamma$-ray energies for the decay of ${}^{82}\mathrm{Br}$. The hatched region shows the ROI fraction for a $\delta =0.02$.

Figure 4

The sum spectrum of $\beta$ and $\gamma$-ray energies for the decay of ${}^{100}\mathrm{Tc}$. The hatched region shows the ROI fraction for a $\delta =0.02$.

Figure 5

The sum spectrum of $\beta$ and $\gamma$-ray energies for the decay of ${}^{150}\mathrm{Pm}$. The hatched region shows the ROI fraction for a $\delta =0.02$.