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

The double beta decay of 100Mo to the 01+ and 21+ 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 T1 / 2(2 ν) = [5.7-0.9+1.3 (stat.) ± 0.8 (syst.)] × 1020  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 T1 / 2(0 ν) (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 T1 / 2(2 ν) (0+ → 21+) > 1.1 × 1021  y (at 90% C.L.) and for the neutrinoless mode T1 / 2(0 ν) (0+ → 21+) > 1.6 × 1023  y (at 90% C.L.). © 2006 Elsevier B.V. All rights reserved.