Measurement of double beta decay of 100Mo to excited states in the NEMO 3 experiment

The double beta decay of 100 Mo to the 0 +1 and 2 +1 excited states of 100 Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of 100 Mo to the excited 0 +1 state is measured to be T (2 ν ) 1 / 2 = [5.7 +1 . 3 − 0 . 9 (stat) ± 0.8(syst)] · 10 20 y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0 +1 state has been found. The corresponding half-life limit is T (0 ν ) 1 / 2 (0 + → 0 +1 ) > 8 . 9 · 10 22 y (at 90% C.L.). The search for the double beta decay to the 2 +1 excited state has allowed the determination of limits on the half-life for the two neutrino mode T (2 ν ) 1 / 2 (0 + → 2 +1 ) > 1 . 1 · 10 21 y (at 90% C.L.) and for the neutrinoless mode T (0 ν ) 1 / 2 (0 + → 2 +1 ) > 1 . 6 · 10 23 y (at 90% C.L.).