Final results on the 0ν β β decay half-life limit of ¹⁰⁰Mo from the CUPID-Mo experiment

The CUPID-Mo experiment to search for 0 ν β β ν β β decay in ¹⁰⁰ 100 Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0 ν β β ν β β decay experiment. CUPID-Mo was comprised of 20 enriched Li_2 Li 2 ¹⁰⁰ 100 MoO₄ MoO 4 scintillating calorimeters, each with a mass of ~ 0.2 ∼ 0.2 kg, operated at ~ 20 ∼ 20 mK. We present here the final analysis with the full exposure of CUPID-Mo ( ¹⁰⁰ 100 Mo exposure of 1.47 kg × year kg × year ) used to search for lepton number violation via 0 ν β β ν β β decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the ¹⁰⁰ 100 Mo 0 ν β β ν β β decay half-life of T1/20ν T 1 / 2 0 ν > 1.8× 10²⁴ > 1.8 × 10 24 year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of m β β <~(0.28-0.49) < ( 0.28 - 0.49 ) eV, dependent upon the nuclear matrix element utilized.