Measurement of the Top Pair Cross Section with 2.7 fb-1 in the Lepton Plus Jets Decay Channel (public web page)

Measurement of the Top Pair Cross Section in the Lepton Plus Jets Decay Channel with 2.7 fb^-1

Tom Schwarz, Andrew Ivanov
Robin Erbacher

University of California - Davis

Documentation

Public Conference Note

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Abstract

The cross-section for pair produced top quarks has been measured in 2.7 fb^-1 of collected data from the high Pt lepton triggers. The measurement is performed in the lepton plus jets decay channel using events where at least on jet has been "tagged" with a secondary vertex as evidence of a bottom quark decay. Events are selected by requiring a high Pt (> 20 GeV) lepton (electron or muon), at least 25 GeV in missing transverse energy, >=3 jets with Et > 20 GeV. In addition, the sum of the transverse energy in the event must be > 250 GeV to further reduce backgrounds and optimize systematic uncertainties. A data-driven approach is used to estimate the background content, with special care taken to handling W boson plus heavy flavor, Non-W estimate, and events with a mis-tagged secondary vertex. A likelihood is used to extract the measured result and the statistical uncertainty. The result is &sigma_tt = 7.2 ± 0.4_stat ± 0.5_syst ± 0.4_lumi.

Result

The measured top pair cross section in the lepton plus jets channel using 2.7 fb^-1 of CDF collected data is:

&sigma_tt = 7.2 ± 0.4_stat ± 0.5_syst ± 0.4_lumi

&Delta &sigma/&sigma = 10 %

Plots & Tables
pdf	Histogram of expected and observed number of events as a function of jet multiplicity for events with at least one secondary vertex "tag", and additional selection Ht > 250 GeV, and MET > 25 GeV.
tex	Table of the expected and observed number of events as a function of jet multiplicity for events with at least one secondary vertex "tag", and additional selection Ht > 250 GeV, and MET > 25 GeV.
pdf	The measured cross-section and statistical uncertainty are derived from a likelihood fit. This is a plot of the log likelihood as a function of the cross-section.
pdf	Systematic uncertainties on the measured cross-section.
pdf	Output of the Neural Network flavor separator, used to calculate the heavy flavor fraction in data in W+1 jet events. A correction factor is derived by comparing the result of the neural network fit to the Monte Carlo prediction. The correction factor is cross-checked in the W+2 jet sample and then applied to the signal region W + >=3 jets.
pdf	Histogram of the expected and observed number of events as a function of jet multiplicity for events with at least one secondary vertex "tag", no Ht cut, and MET > 20 GeV. This selection is primarily used for other top properties analysis and therefore, is here for convienice.
tex	Table of the Expected and observed number of events as a function of jet multiplicity for events with at least one secondary vertex "tag", no Ht cut, and MET > 20 GeV. This selection is primarily used for other top properties analysis and therefore, is here for convienice.