$Q_{\textrm{EC}}$-value determination for $^{21}$Na$\rightarrow^{21}$Ne and $^{23}$Mg$\rightarrow^{23}$Na mirror-nuclei decays using high-precision mass spectrometry with ISOLTRAP at ISOLDE/CERN

We report on high-precision QEC values of the Na21→Ne21 and Mg23→Na23 mirror β transitions from mass measurements with ISOLTRAP at the CERN ISOLDE facility. A precision of δm/m=9×10−10 and δm/m=1.5×10−9 was reached for the masses of Na21 and Mg23, respectively. We reduce the uncertainty of the QEC values by a factor of 5, making them the most precise experimental input data for the calculation of the corrected Ft value of these mixed Fermi and Gamow-Teller transitions. For the Na21→Ne21QEC value, a 2.3σ deviation from the literature QEC value was found.