Precise mass measurement of ⁷⁵As for evaluation of ultra-low Q value β-decay branches in ⁷⁵Se and ⁷⁵Ge

Ultra-low Q value β decays or electron captures (EC) occur to an excited state in the daughter nucleus with an energy ≲ 1 keV. These decays are of potential interest as candidates for direct neutrino mass determination experiments since a low Q value results in a higher density of counts near the end-point of the β-spectrum where the effect of a non-zero neutrino mass would be observed. A number of potential candidates have been identified. However, the determination of whether these decays are energetically allowed with Q < 1 keV is often limited by uncertainty in the parent and daughter atomic masses. In the case of ⁷⁵Se and ⁷⁵Ge, both have potential ultra-low Q value decay branches to distinct final states in ⁷⁵As. The uncertainty in the Q values is currently limited by the 0.9 keV uncertainty in the mass of the stable daughter ⁷⁵As. The masses of ⁷⁵Se and ⁷⁵Ge on the other hand are known to 73 eV/c² and 52 eV/c², respectively. To determine whether these decays are energetically allowed and if they could be ultra-low, we have performed a precise measurement of the mass of ⁷⁵As via Penning trap mass spectrometry with the LEBIT facility at the NSCL to a precision of ∼100 eV. We will present the results of this measurement and implications for the decays of ⁷⁵Se and ⁷⁵Ge.