Nuclear Charge Radius of 26mAl and Its Implication for Vud in the Quark Mixing Matrix

Collinear laser spectroscopy was performed on the isomer of the aluminium isotope 26mAl. The measured isotope shift to 27Al in the 3s23p 2P = 3/2 -> 3s24s 2S1/2 atomic transition enabled the first experimental determination of the nuclear charge radius of 26mAl, resulting in Rc = 3.130(15) fm. This differs by 4.5 standard deviations from the extrapolated value used to calculate the isospin-symmetry breaking corrections in the superallowed beta decay of 26mAl. Its corrected Ft value, important for the estimation of Vud in the Cabibbo-Kobayashi-Maskawa matrix, is thus shifted by 1 standard deviation to 3071.4(1.0) s.