UC Berkeley

The CUPID-Mo experiment to search for 0νββ$$ u \beta \beta $$ 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 0νββ$$ u \beta \beta $$ decay experiment. CUPID-Mo was comprised of 20 enriched Li2$$\hbox {Li}_{{2}}$$100$$^{100}$$MoO4$$\hbox {MoO}_4$$ scintillating calorimeters, each with a mass of ∼0.2$$\sim 0.2$$ kg, operated at ∼20$$\sim 20$$ mK. We present here the final analysis with the full exposure of CUPID-Mo (100$$^{100}$$Mo exposure of 1.47 kg×year$$\hbox {kg} \times \hbox {year}$$) used to search for lepton number violation via 0νββ$$ u \beta \beta $$ 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 0νββ$$ u \beta \beta $$ decay half-life of T1/20ν$$T_{1/2}^{0 u }$$>1.8×1024$$> {1.8}\times 10^{24}$$ year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of mββ$$\left$$  <(0.28-0.49)$$<~{(0.28{-}0.49)} $$ eV, dependent upon the nuclear matrix element utilized.