Simultaneous Measurement of the Ratio R=B(t→Wb)/B(t→Wq) and the Top-Quark Pair Production Cross Section with the D0 Detector at s=1.96TeV
Abstract: We present the first simultaneous measurement of the ratio of branching fractions, R = B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(t (t) over bar) in the lepton plus jets channel using 0.9 fb(-1) of p (p) over bar collision data at root s = 1.96 TeV collected with the D0 detector. We extract R and sigma(t (t) over bar) by analyzing samples of events with 0, 1, and >= 2 identified b jets. We measure R = 0.97(-0.08)(+0.09) (stat + syst) and sigma(t (t) over bar) = 8.18(-0.84)(+0.90) (stat + syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.
Summary (1 min read)
- The lepton isolation criteria are based on calorimeter and tracking information.
- It combines variables that characterize the presence and properties of secondary vertices and tracks with high impact parameter inside the jet.
- Single top-quark production is modeled with the SINGLETOP  event generator.
- Additional corrections  are applied to the reconstructed objects to improve the agreement between data and simulation.
- The authors further subtract diboson, single top quark and Z jets contribu- tions, normalized to the next-to-leading-order cross sections  .
- Only the four highest-p T jets are considered for these variables to reduce the sensitivity to soft radiation.
- The authors evaluate it for each physics process considered and build corresponding template distributions consisting of ten bins.
- The discriminant shape for the multijet background is obtained from a sample of data events where the lepton fails the isolation criteria.
- The systematic uncertainties are incorporated in the fit using nuisance parameters  , each represented by a Gaussian term in the likelihood.
- The largest uncertainty comes from the limited statistics.
- Part of the im-provement results from a fourfold reduction in the systematic uncertainties due to b-tagging, which is mostly absorbed by the R measurement.
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