New measurement of double-β decays of Mo100 to excited states of Ru100 with the CUPID-Mo experiment

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 Li2 100MoO4 (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-β decays of 100Mo to the first 0+ and 2+ excited states of 100Ru using the full CUPID-Mo exposure (2.71 kg yr of LMO). We measure the half-life of 2νββ decay to the 0+ state as T 2ν→01+ = (7.5 ± 1 1/2 0.8 (stat.) +0.4 (syst.)) × 1020 yr. The bolometric technique enables measurement of the electron energies as well −0.3 as the γ rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the 21+ state of T 2ν→21+ > 4.4 × 1021 yr (90% c.i.) and on the neutrinoless modes of T 0ν→21+ > 2.1 × 1023 yr (90% c.i.), T 0ν→01+ > 1.2 × 1023 yr (90% c.i.). Information on the electrons’ spectral shape is obtained, which allows us to 1/2 make the first comparison of the single and higher state dominance 2νββ decay models for the 01+ excited state of 100Ru.