New observation of 2β2ν decay of 100Mo to the level of 100Ru in the ARMONIA experiment

A sample of 100MoO3 powder with molybdenum enriched in 100Mo to 99.5% and mass of 1199 g was measured for 18120 h in a low-background set-up with 4 HP Ge detectors (≃225cm3 volume each one) deep underground (3600 m w.e.) at the Laboratori Nazionali del Gran Sasso of the INFN (Italy). The two γ quanta of 540 keV and of 591 keV emitted in the deexcitation process after a 2β2ν decay of 100Mo to the excited level of 100Ru (Eexc=1131keV) are observed in the accumulated data both in coincidence and in the 1-dimensional sum spectrum. The measured half life is: , well in agreement with positive results obtained in previous experiments. Moreover, the limit on charge non-conserving β decay of 100Mo is also set: τCNC>4.5×1019yr at 90% C.L.; it corresponds to the limit on CNC admixture in weak currents: .