Direct high-precision measurement of the mass difference of 77As–77Se related to neutrino mass determination

Abstract

The first direct determination of the ground-state-to-ground-state β−-decay Q-value of 77As to 77Se was performed by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The resulting Q-value is 684.463(70) keV, representing a remarkable 24-fold improvement in precision compared to the value reported in the most recent Atomic Mass Evaluation (AME2020). With the significant reduction of the uncertainty of the ground-state-to-ground-state Q-value and knowledge of the excitation energies in 77Se from γ-ray spectroscopy, the ground-state-to-excited-state Q-value of the transition 77As (3/2−, ground state) → 77Se∗ (5/2+, 680.1035(17) keV) was refined to be 4.360(70) keV. We confirm that this potential low Q-value β−-decay transition for neutrino mass determination is energetically allowed at a confidence level of about 60σ. Nuclear shell-model calculations with two well-established effective Hamiltonians were used to estimate the partial half-life for the low Q-value transition. The half-life was found to be of the order of 109 years for this first-forbidden non-unique transition, which rules out this candidate a potential source for rare-event experiments searching for the electron antineutrino mass.