High-precision electron-capture $Q$ value measurement of ${}^{111}$In for electron-neutrino mass determination

Abstract

A precise determination of the ground state ${}^{111}$In ($9/2^{+}$) electron capture to ground state of ${}^{111}$Cd ($1/2^{+}$) $Q$ value has been performed utilizing the double Penning trap mass spectrometer, JYFLTRAP. A value of 857.63(17) keV was obtained, which is nearly a factor of 20 more precise than the value extracted from the Atomic Mass Evaluation 2020 (AME2020). The high-precision electron-capture $Q$ value measurement along with the nuclear energy level data of 866.60(6) keV, 864.8(3) keV, 855.6(10) keV, and 853.94(7) keV for ${}^{111}$Cd was used to determine whether the four states are energetically allowed for a potential ultra-low $Q$-value ${\beta }^{}$ decay or electron-capture decay. Our results confirm that the excited states of 866.60(6) keV with spin-parity ($J^{\pi }$) of 3/2${}^{+}$ and 864.8(3) keV with $J^{\pi }$ = 3/2${}^{+}$ are ruled out due to their deduced electron-capture $Q$ value being smaller than 0 keV at the level of around 20$\sigma$ and 50$\sigma$, respectively. Electron-capture decays to the excited states at 853.94(7) keV ($J^{\pi }$ = 7/2${}^{+}$) and 855.6(10) keV ($J^{\pi }$ = 3/2${}^{+}$), are energetically allowed with $Q$ values of 3.69(19) keV and 2.0(10) keV, respectively. The allowed decay transition ${}^{111}$In (9/2${}^{+}$) $\to$ ${}^{111}$Cd (7/2${}^{+}$), with a $Q$ value of 3.69(19) keV, is a potential a new candidate for neutrino-mass measurements by future EC experiments featuring new powerful detection technologies. The results show that the indium level $2p_{1/2}$ for this decay branch leads to a significant increase in the number of EC events in the energy region sensitive to the electron neutrino mass.

12 pages, 4 figures

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