Measurement of the forward-backward asymmetry in e+e− → bb and the b-quark branching ratio to muons at TRISTAN using neural networks

The forward-backward asymmetry in e(+)e(-) --> b (b) over bar at root s = 57.9 GeV and the b-quark branching ratio to muons have been measured using neural networks. Unlike previous methods for measuring the b (b) over bar forward-backward asymmetry where the estimated background from c-quark decays and other sources are subtracted, here events are categorized as either b (b) over bar or non-b (b) over bar events by neural networks based on event-by-event characteristics. The determined asymmetry is -0.429 +/- 0.044(stat) +/- 0.047(sys) and is consistent with the prediction of the standard model. The measured B (B) over bar mixing parameter is 0.136 +/- 0.037(stat) +/- 0.040(sys) +/- 0.002(model) and the measured b-quark branching ratio to muons is 0.122 +/- 0.006(stat) +/- 0.007(sys).