New measurement of double-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>β</mml:mi></mml:math> decays of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Mo</mml:mi><mml:mprescripts/><mml:none/><mml:mn>100</mml:mn></mml:mmultiscripts></mml:math> to excited states of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ru</mml:mi><mml:mprescripts/><mml:none/><mml:mn>100</mml:mn></mml:mmultiscripts></mml:math> with the CUPID-Mo experiment
C. Augier, A. S. Barabash, F. Bellini, G. Benato, M. Beretta, L. Bergé, J. Billard, Yu. A. Borovlev, L. Cardani, N. Casali, A. Cazes, M. Chapellier, D. Chiesa, I. Dafinei, F.A. Danevich, M. De Jésus, T. Dixon, L. Dumoulin, K. Eitel, F. Ferri, B. K. Fujikawa, J. Gascon, L. Gironi, A. Giuliani, V. D. Grigorieva, M. Gros, D. Helis, H. Z. Huang, R.G. Huang, L. Imbert, J. Johnston, A. Juillard, H. Khalife, M. Kleifges, V. Kobychev, Yu.G. Kolomensky, С. И. Коновалов, J. Kotila, P. Loaiza, L. Ma, E. P. Makarov, P. de Marcillac, R. Mariam, L. Marini, S. Marnieros, X.-F. Navick, C. Nones, E. B. Norman, E. Olivieri, J. L. Ouellet, L. Pagnanini, L. Pattavina, B. Paul, M. Pavan, H. Peng, G. Pessina, S. Pirro, D. V. Poda, O. G. Polischuk, S. Pozzi, E. Previtali, T. Redon, A. Rojas, S. Rozov, V. Sanglard, J. A. Scarpaci, B. Schmidt, Yang Shen, V.N. Shlegel, V. Singh, C. Tomei, V.I. Tretyak, V. I. Umatov, L. Vagneron, M. Velázquez, B. Welliver, L. A. Winslow, M. Xue, E. Yakushev, M. M. Zarytskyy, A. Zolotarova
Abstract
The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of $20\phantom{\rule{4pt}{0ex}}{\mathrm{Li}}_{2}^{100}\mathrm{Mo}{\mathrm{O}}_{4}$ (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-$\ensuremath{\beta}$ decays of $^{100}\mathrm{Mo}$ to the first ${0}^{+}$ and ${2}^{+}$ excited states of $^{100}\mathrm{Ru}$ using the full CUPID-Mo exposure ($2.71\phantom{\rule{4pt}{0ex}}\mathrm{kg}\phantom{\rule{0.16em}{0ex}}\mathrm{yr}$ of LMO). We measure the half-life of $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay to the ${0}_{1}^{+}$ state as ${T}_{1/2}^{2\ensuremath{\nu}\ensuremath{\rightarrow}{0}_{1}^{+}}=(7.5\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{4pt}{0ex}}\text{(stat.)}{\phantom{\rule{4pt}{0ex}}}_{\ensuremath{-}0.3}^{+0.4}\phantom{\rule{4pt}{0ex}}\text{(syst.)})\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}\mathrm{yr}$. The bolometric technique enables measurement of the electron energies as well as the $\ensuremath{\gamma}$ rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the ${2}_{1}^{+}$ state of ${T}_{1/2}^{2\ensuremath{\nu}\ensuremath{\rightarrow}{2}_{1}^{+}}>4.4\ifmmode\times\else\texttimes\fi{}{10}^{21}\phantom{\rule{4pt}{0ex}}\mathrm{yr}\phantom{\rule{4pt}{0ex}}(90% \text{c.i.})$ and on the neutrinoless modes of ${T}_{1/2}^{0\ensuremath{\nu}\ensuremath{\rightarrow}{2}_{1}^{+}}>2.1\ifmmode\times\else\texttimes\fi{}{10}^{23}\phantom{\rule{4pt}{0ex}}\mathrm{yr}\phantom{\rule{4pt}{0ex}}(90% \text{c.i.})$, ${T}_{1/2}^{0\ensuremath{\nu}\ensuremath{\rightarrow}{0}_{1}^{+}}>1.2\ifmmode\times\else\texttimes\fi{}{10}^{23}\phantom{\rule{4pt}{0ex}}\mathrm{yr}\phantom{\rule{4pt}{0ex}}(90% \text{c.i.})$. Information on the electrons' spectral shape is obtained, which allows us to make the first comparison of the single and higher state dominance $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay models for the ${0}_{1}^{+}$ excited state of $^{100}\mathrm{Ru}$.