A Study of the LEP and SLD Measurements of $A_b$

TL;DR

This paper systematically examines the measurements of the parameter $A_b$ from LEP and SLD experiments, analyzing data dependence, systematic errors, and the significance of deviations from the Standard Model, concluding that current data unlikely indicate new physics.

Contribution

It provides a comprehensive analysis of $A_b$ measurements, addressing data dependence, systematic errors, and the impact of individual measurements on the observed deviation.

Findings

Deviation from Standard Model is between 1.7σ and 2.9σ depending on data selection.

Current data sets are extensive, making new physics explanations unlikely.

Systematic uncertainties and measurement choices significantly influence the deviation.

Abstract

A systematic study is made of the data dependence of the parameter $A_{\rm{b}}$, that, since 1995, has shown a deviation from the Standard Model prediction of between 2.4 and 3.1 standard deviations. Issues addressed include: the effect of particular measurements, values found by individual experiments, LEP/SLD comparison, and the treatment of systematic errors. The effect, currently at the 2.4$\sigma$ level, is found to vary in the range from 1.7$\sigma$ to 2.9$\sigma$ by excluding marginal or particularly sensitive data. Since essentially the full LEP and SLD Z decay data sets are now analysed the meaning of the deviation, (new physics, or marginal statistical fluctuation) is unlikely to be given by the present generation of colliders.