Precision QEC-value measurement of Mg23 for testing the Cabibbo-Kobayashi-Maskawa matrix unitarity

We report a new direct measurement of the transition energy QEC of the Mg23 β+ decay, using the TITAN Penning-trap mass spectrometer. This value is found to agree with the latest atomic mass evaluation while being four times more precise. The increase in precision changes the uncertainty contribution of the QEC value on the statistical rate function fv from 11% to 0.6%, an improvement by a factor of 18. This enables a more robust determination of the corrected Ft value of this mirror transition to the required precision, making possible further test of the Cabibbo-Kobayashi-Maskawa matrix unitarity.