Measurement of Ab_FB using inclusive b-hadron decays

TL;DR

This paper reports a precise measurement of the forward-backward asymmetry in Z boson decays to b-quarks using inclusive decay data, neural network tagging, and vertex information, resulting in an accurate determination of the weak mixing angle.

Contribution

It introduces a neural network-based method for tagging b-quark events and combines vertex and kaon data to measure the asymmetry with high precision.

Findings

Measured the pole b asymmetry A^{0,b}_{FB} = 0.1009 ± 0.0027 (stat) ± 0.0015 (syst)

Determined the effective weak mixing angle sin^2(θ_W^{eff}) = 0.23193 ± 0.00056

Achieved high-performance b-quark tagging over a wide angular range

Abstract

Based on a sample of four million events collected by ALEPH from 1991 to 1995, a measurement of the forward-backward asymmetry in Z -> b-barb decays using inclusive final states is presented. High-performance tagging of b-barb events in a wide angular range is achieved using neural network techniques. An optimal hemisphere charge estimator is built by merging primary and secondary vertex information, leading kaon identification and jet charge in a neural network. The average charge asymmetry, the flavour tagging efficiencies and mean b-hemisphere charges are measured from data and used to extract the pole b asymmetry in the Standard Model A^{0,b}_{FB} = 0.1009 +- 0.0027 (stat) +- 0.0015 (syst), corresponding to a value of the effective weak mixing angle of sin^2(theta_W^{eff}) = 0.23193 +- 0.00056.