High Precision Branching Ratio Measurement for the Superallowed Beta Decay of Rb-74: A Prerequisite for Exacting Tests of the Standard Model
Abstract
Studies of superallowed β decays indicate that the CKM quark mixing matrix is not unitary. To perform tests of unitarity, the Q_EC, T_1/2, and branching ratio of the 0^+ to 0^+ analog transition must be measured with great precision and calculated corrections must be applied. We report experimental results from γ and conversion electron studies of the superallowed β emitter ^74Rb performed at ISAC/TRIUMF. The detection equipment consisted of two Si(Li) conversion electron spectrometers, an HPGe detector, and two plastic scintillator trigger detectors. A moving tape was used to remove long lived contaminants and daughter activities. Seven γ rays and two converted transitions were observed following the Gamow-Teller decay of ^74Rb. They determine, in conjunction with a recent shell model calculation, the branching ratio of the analog transition to be 99.5(1)%. The experimental upper limits for the Fermi decay to the 0^+2 and (0^+_3) levels are in agreement with recent theoretical predictions. The Q_EC value of the ^74Rb decay is predicted to be 10405(9) keV. The implications of the results to the feasibility of a precise test of CKM unitarity using ^74Rb will be discussed.
- Publication:
-
APS April Meeting Abstracts
- Pub Date:
- April 2003
- Bibcode:
- 2003APS..APRT10001P