Direct measurement of the mass difference of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>As</mml:mi><mml:mprescripts/><mml:none/><mml:mn>72</mml:mn></mml:mmultiscripts><mml:mtext>−</mml:mtext><mml:mmultiscripts><mml:mi>Ge</mml:mi><mml:mprescripts/><mml:none/><mml:mn>72</mml:mn></mml:mmultiscripts></mml:mrow></mml:math> rules out <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>As</mml:mi><mml:mprescripts/><mml:none/><mml:mn>72</mml:mn></mml:mmultiscripts></mml:math> as a promising <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>β</mml:mi></mml:math>-decay candidate to determine the neutrino mass
Z. W. Ge, T. Eronen, A. de Roubin, D. A. Nesterenko, M. Hukkanen, O. Beliuskina, R. P. de Groote, S. Geldhof, W. Gins, A. Kankainen, Á. Koszorús, J. Kotila, Joel Kostensalo, I. D. Moore, A. Raggio, S. Rinta-Antila, J. Suhonen, V. Virtanen, A. Weaver, A. Zadvornaya, A. Jokinen
Abstract
We report the first direct determination of the ground-state to ground-state electron-capture $Q$ value for the $^{72}\mathrm{As}$ to $^{72}\mathrm{Ge}$ decay by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The $Q$ value was measured to be 4343.596(75) keV, which is more than a fiftyfold improvement in precision compared to the value in the most recent Atomic Mass Evaluation 2020. Furthermore, the new $Q$ value was found to be 12.4(40) keV (3.1 $\ensuremath{\sigma}$) lower. With the significant reduction of the uncertainty of the ground-state to ground-state $Q$ value combined with the level scheme of $^{72}\mathrm{Ge}$ from $\ensuremath{\gamma}$-ray spectroscopy, we confirm that the five potential ultralow $Q$-value ${\ensuremath{\beta}}^{+}$ decay or electron capture transitions are energetically forbidden, thus precluding all the transitions as possible candidates for the electron neutrino mass determination. However, the discovery of small negative $Q$ values opens up the possibility to use $^{72}\mathrm{As}$ for the study of virtual $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ transitions.