High-precision half-life measurement for the isospin T = 1/2 mirror $\beta^+$ decay of $^{21}$Na

Accepted for publication in Physical Review CInternational audienceThe half-life of the isospin T = 1/2 mirror $\beta^+$ decay of 21Na was measured at the GANIL-SPIRAL radioactive ion beam facility to be T1=2 = 22.422 (10) s, a result that is more than afactor of 5 times more precise than the previous world average, with a resulting ft value that isnow two times more precise. The precision of this new result implies that the half-life is no longerthe dominant source of uncertainty in the Ft value used in the calculation of Vud from mirrordecays to test the conserved vector current hypothesis of the Standard Model. The value of Vuddeduced from mirror decays using the new half-life result is now in better agreement with the Vudderived from T = 1 superallowed 0+ to 0+ transitions