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

The double beta decay of 100Mo to the 01 and 2 + 1 excited states of 100Ru 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 100Mo to the excited 01 state is measured to be T (2ν) 1/2 = [5.7 +1.3 −0.9(stat)±0.8(syst)]·10 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 01 state has been found. The corresponding half-life limit is T (0ν) 1/2 (0 + → 01 ) > 8.9 · 1022 y (at 90% C.L.). The search for the double beta decay to the 21 excited state has allowed the determination of limits on the half-life for the two neutrino mode T (2ν) 1/2 (0 + → 21 ) > 1.1·1021 y (at 90% C.L.) and for the neutrinoless mode T (0ν) 1/2 (0+ → 2 + 1 ) > 1.6·1023 y (at 90% C.L.).