Direct determination of the atomic mass difference of the pairs ${}^{76}$As-${}^{76}$Se and ${}^{155}$Tb-${}^{155}$Gd rules out ${}^{76}$As and ${}^{155}$Tb as possible candidates for electron (anti)neutrino mass measurements

Abstract

The first direct determination of the ground-state-to-ground-state $Q$ values of the $β^-$ decay ${}^{76}$As $\to$ ${}^{76}$Se and the electron-capture decay ${}^{155}$Tb $\to$ ${}^{155}$Gd was performed utilizing the double Penning trap mass spectrometer JYFLTRAP. By measuring the atomic mass difference of the decay pairs via the phase-imaging ion-cyclotron-resonance (PI-ICR) technique, the $Q$ values of ${}^{76}$As $\to$ ${}^{76}$Se and ${}^{155}$Tb $\to$ ${}^{155}$Gd were determined to be 2959.265(74) keV and 814.94(18) keV, respectively. The precision was increased relative to earlier measurements by factors of 12 and 57, respectively. The new $Q$ values are 1.33 keV and 5 keV lower compared to the values adopted in the most recent Atomic Mass Evaluation 2020. With the newly determined ground-state-to-ground-state $Q$ values combined with the excitation energy from ${\hat{I}}^3$-ray spectroscopy, the $Q$ values for ground-state-to-excited-state transitions ${}^{76}$As (ground state) $\to$ ${}^{76}$Se${}^{\ast }$ (2968.4(7) keV) and ${}^{155}$Tb (ground state) $\to$ ${}^{155}$Gd${}^{\ast }$ (815.731(3) keV) were derived to be -9.13(70) keV and -0.79(18) keV. Thus we have confirmed that both of the $β^{-}$-decay and EC-decay candidate transitions are energetically forbidden at a level of at least 4$\ddot{I}ƒ$, thus definitely excluding these two cases from the list of potential candidates for the search of low-$Q$-value $β^-$ or EC decays to determine the electron-(anti)neutrino mass.

8 pages, 4 figures, to be submitted