New measurement of double- decays of ¹⁰⁰Mo to excited states of ¹⁰⁰Ru 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 Li-2 Mo-100 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-beta decays of Mo-100 to the first 0(+) and 2(+) excited states of Ru-100 using the full CUPID-Mo exposure (2.71 kg yr of LMO). We measure the half-life of 2 nu beta beta decay to the 0(1)(+) state as T-1/2(2 nu -> 01+) = (7.5 +/- 1 0.8 (stat.)(-0.3)(+0.4) (syst.)) x 10(20) yr. The bolometric technique enables measurement of the electron energies as well as the 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 nu -> 21+) > 4.4 x 10(21) yr (90% c.i.) and on the neutrinoless modes of T-1/2(0 nu -> 21+) > 2.1 x 10(23) yr (90% c.i.), T-1/2(0 nu -> 01+) > 1.2 x 10(23) yr (90% c.i.). Information on the electrons' spectral shape is obtained, which allows us to 1 make the first comparison of the single and higher state dominance 2 nu beta beta decay models for the 0(1)(+) excited state of Ru-100.