Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mi>ν</mml:mi><mml:mi>β</mml:mi><mml:mi>β</mml:mi></mml:mrow></mml:math> Decay Rate and Spectral Shape of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Mo</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>100</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> from 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, E. Celi, 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. 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, Yandi Shen, V. N. Shlegel, F. Šimkovic, V. Singh, C. Tomei, V.I. Tretyak, V. I. Umatov, L. Vagneron, M. Velázquez, Brent Ware, B. Welliver, L. A. Winslow, M. Xue, E. Yakushev, M. M. Zarytskyy, A. Zolotarova
Abstract
Neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino double beta decay ($2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay half-life of $^{100}\mathrm{Mo}$ to the ground state of $^{100}\mathrm{Ru}$ of $[7.07\ifmmode\pm\else\textpm\fi{}0.02(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.11(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{yr}$ by the CUPID-Mo experiment. With a relative precision of $\ifmmode\pm\else\textpm\fi{}1.6%$ this is the most precise measurement to date of a $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay rate in $^{100}\mathrm{Mo}$. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ${\ensuremath{\xi}}_{3,1}=0.45\ifmmode\pm\else\textpm\fi{}0.03(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.05(\mathrm{syst})$ based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. We also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay.