Direct measurement of the mass difference of 72As-72Ge rules out 72As as a promising β-decay candidate to determine the neutrino mass

Preprint of paper published on Physical Review C

We report the first direct determination of the ground-state to ground-state electron-capture Q-value for the 72As to 72Ge decay by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The Q-value was measured to be 4343.596(75) keV, which is more than a 50-fold improvement in precision compared to the value in the most recent Atomic Mass Evaluation 2020. Furthermore, the new Qvalue was found to be 12.4(40) keV (3.1 σ) lower. With the significant reduction of the uncertainty of the ground-state to ground-state Q-value value combined with the level scheme of 72Ge from γ-ray spectroscopy, we confirm that the five potential ultra-low Q-value β +-decay or electron capture transitions are energetically forbidden, thus precluding all the transitions as possible candidates for the electron neutrino mass determination. However, the discovery of small negative Q-values opens up the possibility to use 72As for the study of virtual β-γ transitions