In this analysis we measure the t-tbar production cross section using lepton+jets events.  Lepton plus jets events result from top decays (t->Wb) in t-tbar events when one of the W bosons decays to an electron or muon plus neutrino (taus are not included) and the other decays hadronically, resulting in a topology of one high-Pt electron or muon, missing transverse energy and four jets.  We require 3 or more jets to allow for the possibility that one of the jets is not found.  The dominant background for this process is QCD production of W+jets.  We enhance the signal to background ratio in this analysis by identification of one of the jets in the event as a candidate b-jet. The identification of candidate b-jets ("b-tagging") is done by looking for relatively low momentum muons in or near the jets that result from semileptonic decays of B hadrons.  This identification is referred to as "Soft Lepton Tagging" (SLT).

 

The dataset consists of 125 pb^-1 of proton-antiproton collisions at
root(s)=1.96 TeV.  In events with a 3 or more jets and at least one
SLT-tagged jet, we measure the t-tbar production cross section to be:

where the first uncertainty is statistical and the second systematic.

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CDF event display views of one of our candidates.

The tight lepton is a muon (CMUP). There are 4 jets in the event where the 2^nd highest E_T jet has an identified secondary vertex (SecVtx) and the 3^rd highest E_T jet has the SLTm tag (CMUP) with a p_T of 6.7 GeV/c.

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l+ Jets event selection

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SLTm tagger & b-tagging

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Results & systematic contributions

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SLT_m tagged events per jet multiplicity.

The color stack histograms represent the different background contributions in each jet bin.

The hashed boxes are ±1s error (statistical & systematic) on the background estimate. The stars are the data events.

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SLT_m tagged events per jet multiplicity showing the total background plus ttbar contribution to each jet bin.

The ttbar contribution is normalized to the theoretical cross section of 6.7 pb at 1.96 TeV.

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Number of tagged events and background summary.

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Comparison of the jet E_T distribution in W + ³ 3 jets for tagged events and for the expectations from fakes+Wbbar+Wccbar, non-W and ttbar events (scaled to the measure cross section of 4.1 pb).

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Comparison of the H_T distribution in W + ³ 3 jets for tagged events and for the expectations from fakes+Wbbar+Wccbar, non-W and ttbar events (scaled to the measure cross section of 4.1 pb).

H_T is defined as the sum of the lepton E_T or p_T, jet E_T and missing E_T.

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Comparison of the SLTm p_T distribution in W + ³ 3 jets for tagged events and for the expectations from fakes+Wbbar+Wccbar, non-W and ttbar events (scaled to the measure cross section of 4.1 pb).

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Comparison of the SLTm d0 significance distribution in W + ³ 3 jets for tagged events and for the expectations from fakes+Wbbar+Wccbar, non-W and ttbar events (scaled to the measure cross section of 4.1 pb).

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SLTm efficiency for the central muon detector (CMU & CMP) as a function of p_T measure from JPsi & Z⁰

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SLTm efficiency for the extended muon detector (CMX) as a function of p_T measure from JPsi & Z⁰

University of Pheonix