The current evaluation of Vud

TL;DR

This paper reviews multiple experimental methods to determine the Vud element of the CKM matrix, emphasizing the high precision and consistency of superallowed nuclear beta decay measurements, and recommends a precise value based on a comprehensive data survey.

Contribution

It provides a new, highly precise survey of superallowed decay data, establishing a robust Vud value with improved accuracy and consistency across multiple transitions.

Findings

All 14 superallowed transitions are statistically consistent.

The survey achieves a precision of about 0.1% in Ft values.

The recommended Vud value is 0.97417(21).

Abstract

The Vud element of the Cabibbo-Kobayashi-Maskawa matrix can be determined from several different experimental approaches: either 0+-to-0+ superallowed nuclear beta decays, neutron decay, nuclear mirror decays, or pion beta decay. Currently all give consistent results but, because the nuclear superallowed value has an uncertainty at least a factor of seven less than all other results, it dominates the result. A new survey of world superallowed-decay data establishes the Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better; and all 14 are statistically consistent with one another. This very robust data set yields the result Vud = 0.97417(21), the value we recommend.