AN IMPROVED STUDY OF THE STRUCTURE OF e+e− → bbg EVENTS AND LIMITS ON THE ANOMALOUS CHROMOMAGNETIC COUPLING OF THE b-QUARK∗

The structure of three-jet ee → bbg events has been studied using hadronic Z 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 b; 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 beyondleading-order QCD calculations are needed to reproduce the features seen in the data. The energy distribution is sensitive to an anomalous b chromomagnetic moment κ at the bb̄g vertex. We measured κ to be consistent with zero and set 95% C.L. limits on its value, −0.05 < κ < 0.04. Submitted to Physical Review D ∗ Work supported in part by Department of Energy contract DE-AC03-76SF00515.