Nuclear beta decays and CKM unitarity

Understand

Nuclear beta decays between (J^pi,T) = (0^+,1) analog states yield the best value for the Vud element of the Cabibbo-Kobayashi-Maskawa matrix.

• Current world data establish the corrected Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better.
• The validity of the small theoretical correction terms is confirmed by excellent consistency among the 14 Ft values and by recent measurements that compare pairs of mirror superallowed transitions.
• With consistency established, the results now yield |Vud| = 0.97420(21).