$Q_{\textrm{EC}}$-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 $Q_{\\textrm{EC}}$ values of the $^{21}$Na$\\rightarrow^{21}$Ne and $^{23}$Mg$\\rightarrow^{23}$Na mirror $\\beta$-transitions from mass measurements with ISOLTRAP at ISOLDE/CERN. A precision of $\\delta m/m = 9 \\cdot 10^{-10}$ and $\\delta m/m = 1.5 \\cdot 10^{-9}$ was reached for the masses of $^{21}$Na and $^{23}$Mg, respectively. We reduce the uncertainty of the $Q_{\\textrm{EC}}$ values by a factor five, making them the most precise experimental input data for the calculation of the corrected $\\mathcal{F} t$-value of these mixed Fermi/Gamow-Teller transitions. For the $^{21}$Na$\\rightarrow^{21}$Ne $Q_{\\textrm{EC}}$ value, a $2.3 \\sigma$ deviation from the literature $Q_{\\textrm{EC}}$-value was found.