decay of (38)Ca: sensitive test of isospin symmetry-breaking corrections from mirror superallowed 0+ 0+ transitions.
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abstract
We report the first branching-ratio measurement of the superallowed 0+0+ transition from Ca38. The result, 0.7728(16), leads to an ft value of 3062.3(68)s with a relative precision of 0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, Ca3838mK and K38mAr38, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.