Precise Half-Life Measurement of the Superallowed Beta+ Emitter 26Si

TL;DR

This paper reports a highly precise measurement of the half-life of 26Si, a superallowed beta+ emitter, achieving the accuracy needed for testing CKM matrix unitarity, with the main remaining uncertainty in the branching ratio.

Contribution

The study provides a half-life measurement of 26Si with 0.03% precision, surpassing the 0.1% accuracy needed for CKM tests, using a high-efficiency gas counter and linked decay analysis.

Findings

Half-life of 26Si measured as 2245.3(7) ms.

Achieved 0.03% precision in half-life measurement.

Results compatible with CKM unitarity tests.

Abstract

We have measured the half-life of the superallowed 0+ -to- 0+ beta+ emitter 26Si to be 2245.3(7) ms. We used pure sources of 26Si and employed a high-efficiency gas counter, which was sensitive to positrons from both this nuclide and its daughter 26mAl. The data were analyzed as a linked parent-daughter decay. To contribute meaningfully to any test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the ft value of a superallowed transition must be determined to a precision of 0.1% or better. With a precision of 0.03% the present result is more than sufficient to be compatable with that requirement. Only the branching ratio now remains to be measured precisely before a +/-0.1% ft value can be obtained for the superallowed transition from 26Si.