Double-Beta Decay Studies of $^{100}$Mo to Excited 0$^{+ }$ States in $^{100}$Ru

We are in the process of analyzing 1 kg x year of two-neutrino double-beta (2$\nu \beta \beta )$ decay data recently obtained at TUNL for $^{100}$Mo. Transitions to excited 0$^{+}$ states in $^{100}$Ru have half-life times which are at least one order of magnitude larger than those to the ground state of $^{100}$Ru. Our experiment features a 1kg sample of $^{100}$Mo placed between two HPGe detectors with a surrounding NaI annulus to veto background events. Passive shielding and coincidence techniques were used to minimize BG events. As the $^{100}$Mo nucleus double-beta decays to the first excited 0$^{+ } \quad ^{100}$Ru*, two gamma rays of 590.8 keV and 539.5 keV are subsequently emitted and detected in coincidence in our two HPGe detectors. We identified 15 (2$\nu \beta \beta )$ events for this transition, therefore, improving the statistical accuracy of the previously reported results of T$_{1/2 }$= 5.9$_{-1.1 }^{+1.7 }$x10$^{20}$ yrs of DeBraekeleer et al$^{2}$. We also give improved limits on T$_{1/2}$ for the transitions to the 2$^{nd}$ and 3$^{rd }$excited 0$^{+}$ states in $^{100}$Ru.\newline \newline Referenced: L. DeBraekeleer et al., Phys. Rev. Lett. 86, 3510 (2001)