Superallowed 0⁺ → 0⁺ β decay and CKM unitarity: A new overview including more exotic nuclei

Abstract.

The ft values for superallowed 0⁺ → 0⁺ nuclear β transitions are nearly independent of nuclear-structure ambiguities and depend uniquely on the vector part of the weak interaction. They thus provide access to clean tests of some of the fundamental precepts of weak-interaction theory and can even probe physics beyond the standard model. We have just completed a new survey and overview of world data on such transitions, including not just the nine cases considered in the past, but also eleven more from T = 1 parents: even-even T_z = - 1 nuclei from ¹⁸Ne to ⁴²Ti; and odd-odd nuclei from ⁶²Ga to ⁷⁴Rb. These new cases all involve more exotic nuclei and, to yield comparable precision, present real experimental challenges. Nevertheless, three of these new cases are already known well enough to contribute - together with the nine well known transitions - to the setting of limits on fundamental weak-interaction parameters. The remaining eight cases show promise for making important contributions in future.