Tests of the standard model from superallowed Fermi β-decay studies: The ~(74)Rb β-decay

摘要

Precise measurements of the intensities of superallowed Fermi 0~+→0~+β-decays have provided a powerful test of the CVD hypothesis at the level of 3 * 10~(-4) and also led to a result in disagreement with unitarity for the CKM matrix at the 98% confidence level. It is essential to address possible trivial explanations for the apparent non-unitaryty such as uncertainties in the isospin symmetry-breaking corrections. We have carefully studied the ~(74)Rb→~(74)Kr β-decay in order to measure the non-analog β-decay branching to the 0~+ state at 508 keV in ~(74)Kr. We have determined that this branching is < 3 * 10~(-4), far smaller than any published theoretical estimate. We also show that high-precision, complete spectroscopy, measuring the major β-branches to excited 0~+ and 1~+ states, must be performed if one is to obtain a meaningful branching ratio to the excited 0~+ state and concomitantly deal, in a substantial way, with the possibility of β feeding to an array of 1~+ states.