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

Abstract

AbstractThe first direct determination of the ground-state-to-ground-state $${\beta ^{-}}$$ β - -decay Q-value of $$^{77}$$ 77 As to $$^{77}$$ 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 $$^{77}$$ 77 Se from $$\gamma $$ γ -ray spectroscopy, the ground-state-to-excited-state Q-value of the transition $$^{77}$$ 77 As (3/2$$^{-}$$ - , ground state) $$\rightarrow $$ → $$^{77}$$ 77 Se$$^{*}$$ ∗ (5/2$$^{+}$$ + , 680.1035(17) keV) was refined to be 4.360(70) keV. We confirm that this potential low Q-value $${\beta ^{-}}$$ β - -decay transition for neutrino mass determination is energetically allowed at a confidence level of about 60$$\sigma $$ σ . 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$$^{9}$$ 9 years for this first-forbidden non-unique transition. Since the half-life of $$^{77}$$ 77 As is only $$\approx $$ ≈ 2 days, usage of it as source for rare-event experiments searching for the electron antineutrino mass would be challenging.