New results for double-beta decay of 100Mo to excited final states of 100Ru using the TUNL-ITEP apparatus

The coincidence detection efficiency of the TUNL-ITEP apparatus designed for measuring half-life times of two-neutrino double-beta (2νββ) decay transitions to excited final states in daughter nuclei has been measured with a factor of 2.4 improved accuracy. In addition, the previous measuring time of 455 days for the study of the 100Mo 2νββ decay to the first excited 01+ state in 100Ru has been increased by 450 days, and a new result (combined with the previous measurement obtained with the same apparatus) for this transition is presented: T1/2=[5.5-0.8+1.2(stat)±0.3(syst)]x1020 yr. Measured 2νββ decay half-life times to excited states can be used to test the reliability of nuclear matrix element calculations needed for determining the effective neutrino mass from zero-neutrino double-beta decay data. We also present new limits for transitions to higher excited states in 100Ru which, if improved, may be of interest for more exotic conjectures, like a bosonic component to neutrino statistics.