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ttbar Cross Section with Secvtx Double Tags |
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Authors: Stephen Miller, Dan Amidei (University of Michigan)
Result: We measure the ttbar cross section in the lepton+jets channel using events with secvtx double tags. We require an isolated electron or muon with transverse momentum above 20 GeV, Missing transverse momentum greater than 20 GeV and three or more jets with transverse energy above 15 GeV. We make the additional requirement that two or more of the jets are tagged with a displaced secondary vertex, indicating the presence of heavy flavor in the jet. This analysis uses the subset of double tagged events in the inclusive Vertex tag cross section measurement. The advantage of the double tag technique is that the backgrounds are greatly reduced and there is little systematic uncertainty on the cross section due to our understanding of the backgrounds.
We measure a cross section of 5.4 +2.4-1.9 (stat) +1.1-0.9 (syst) pb
This is the blessed result for Winter 2004 using 162 pb-1 of data.
The efficiency to double tag ttbar events with 3 or more jets is 0.11 +- 0.02 (This can be compared to an event tagging efficiency of 0.52 for one or more tags)
We estimate the double tag background for 2 or more jets.
Background Estimate: Background Table (tex) (postscript)
Plots
Number
of double tags as a function of njet (eps)
(gif)
Number
of double tags as a function of njet (eps)
(gif) (turn off anti-aliasing to
see error bands)
Transverse lepton Pt (eps) (gif)
