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

Abstract 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 1 / 2 ( 2 ν ) = [ 5.7 −0.9 +1.3 ( 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 1 / 2 ( 0 ν ) ( 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 1 / 2 ( 2 ν ) ( 0 + → 2 1 + ) > 1.1 × 10 21  y (at 90% C.L.) and for the neutrinoless mode T 1 / 2 ( 0 ν ) ( 0 + → 2 1 + ) > 1.6 × 10 23  y (at 90% C.L.).