Direct high-precision measurement of the mass difference of ${}^{77}$As-${}^{77}$Se related to neutrino mass determination

Abstract

The first direct determination of the ground-state-to-ground-state ${β^{-}}$-decay $Q$-value of ${}^{77}$As to ${}^{77}$Se 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 ${}^{77}$Se from ${\hat{I}}^3$-ray spectroscopy, the ground-state-to-excited-state $Q$-value of the transition ${}^{77}$As (3/2${}^{-}$, ground state) $\to$ ${}^{77}$Se${}^{\ast }$ (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 60$\ddot{I}ƒ$. 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 10${}^9$ 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.

8 pages, 4 figures