Measurement
of ttbar Production Cross-Section
in
l+Jets channel with SLTm
b-tagging
Lucio Cerrito, Ulysses Grundler, Tony Liss,
Anyes Taffard,
Greg Veramendi
University of Illinois Urbana-Champaign
This page is for the
measurement of the t-tbar cross section using a muon tag to identify b-jets.
The analysis was blessed for
public consumption on August
5th, 2004.
The Analysis:
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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). In order to further reduce the dominant backgrounds we require HT>200 GeV, where HT is the scalar sum of the lepton pT, jet ET, and missing ET. The dataset consists of 200 pb-1 of proton-antiproton collisions at root(s)=1.96 TeV. In events with a 3 or more jets, HT>200 GeV 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.
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NB: To see hatched histogram on eps files you should disable
Antialias.
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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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SLTm 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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SLTm 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 ET distribution in W+>=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 4.2 pb). |
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Comparison of the HT distribution in W+>=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 4.2 pb). HT is defined as the sum of the lepton
ET or pT, jet ET and missing ET. |
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Comparison of the SLTm pT
distribution in W+>=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 4.2 pb).
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Comparison of the SLTm d0 significance
distribution in W+>=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 4.2 pb). |
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Comparison of the SLTm pTRel (transverse momentum with respect to the jet axis) distribution in W+>=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 4.2 pb). |
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SLTm efficiency for the
central muon detector (CMU & CMP) as a function of pT measure
from JPsi & Z0 |
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SLTm efficiency for the
extended muon detector (CMX) as a function of pT measure from JPsi
& Z0 |
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Last Updated : Wednesday, December 15, 2004 00:32 by Anyes