Measurement of the Bottom Hadron Lifetime at the Z Sup 0 Resonancce PDF Download

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Languages : en
Pages : 214

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Book Description
We have measured the bottom hadron lifetime from b{bar b} events produced at the Z° resonance. Using the precision vertex detectors of the Mark II detector at the Stanford Linear Collider, we developed an impact parameter tag to identify bottom hadrons. The vertex tracking system resolved impact parameters to 30 [mu]m for high momentum tracks, and 70 [mu]m for tracks with a momentum of 1 GeV. We selected B hadrons with an efficiency of 40% and a sample purity of 80%, by requiring there be at least two tracks in a single jet that significantly miss the Z° decay vertex. From a total of 208 hadronic Z° events collected by the Mark II detector in 1990, we tagged 53 jets, of which 22 came from 11 double-tagged events. The jets opposite the tagged ones, referred as the untagged'' sample, are rich in B hadrons and unbiased in B decay times. The variable [Sigma][delta] is the sum of impact parameters from tracks in the jet, and contains vital information on the B decay time. We measured the B lifetime from a one-parameter likelihood fit to the untagged [Sigma][delta] distribution, obtaining [tau]{sub b} = 1.53{sub -0.45}{sup +0.55}{plus minus}0.16 ps which agrees with the current world average. The first error is statistical and the second is systematic. The systematic error was dominated by uncertainties in the track resolution function. As a check, we also obtained consistent results using the [Sigma][delta] distribution from the tagged jets and from the entire hadronic sample without any bottom enrichment.