An improved study of the structure of e+e- -> b bbar g events and limits on the anomalous chromomagnetic coupling of the b-quark

TL;DR

This study analyzes three-jet e+e- -> b bbar g events from Z0 decays to test QCD predictions and sets limits on the anomalous chromomagnetic moment of the b-quark, finding results consistent with the Standard Model.

Contribution

It provides the first measurement of the b-quark's anomalous chromomagnetic moment using three-jet event data from the SLD experiment.

Findings

QCD predictions require beyond-leading-order calculations.

Measured b-quark chromomagnetic moment is consistent with zero.

Set 95% confidence limits: -0.06 < kappa < 0.04.

Abstract

The structure of three-jet e+e- -> b bbar g events has been studied using hadronic Z0 decays recorded in the SLD experiment at SLAC. Three-jet final states were selected and the CCD-based vertex detector was used to identify two of the jets as b or bbar; the remaining jet in each event was tagged as the gluon jet. Distributions of the gluon energy and polar angle with respect to the electron beam were measured over the full kinematic range, and used to test the predictions of perturbative QCD. We find that beyond-leading-order QCD calculations are needed to reproduce the features seen in the data. The energy distribution is sensitive to an anomalous b chromomagnetic moment kappa at the b bbar g vertex. We measured kappa to be consistent with zero and set 95% C.L. limits on its value, -0.06 < kappa < 0.04.