Tom Schwarz, Robin Erbacher
UC Davis
Joey Huston, Mohammad Hussein
Michigan State University
Steve Mrenna
Fermilab
Documentation
Public Conference Note
Send mail to authors
Abstract
The first measurement of the cross section of t-tbar associated with an additional hard jet (t-tbar+jet) has been performed at CDF. The measurement is an important test of perturbative QCD, as NLO effects play an important role in the calculation of the theoretical cross section. In addition, most top events at the LHC will be produced with additional jets, and therefore this process is a substantial background for many new physics signals. The measurement is performed using b-tagged events in the lepton plus jets channel. A data-driven approach is used to predict the background content, and a 2D likelihood is formed to simultaneously measure the t-tbar+jet and tt without jet cross sections. The measured result is &sigmatt+j = 1.6 ± 0.2stat ± 0.5syst pb, which is in agreement with the standard model prediction &sigmatt+j = 1.79 +0.16-0.31 pb [1].
Result
The measured t-tbar + jet cross section in the lepton plus jets channel using 4.1 fb-1 of CDF collected data is:
&sigmatt+j = 1.6 ± 0.2stat ± 0.5syst pb
Which is in agreement with the standard model prediction [1]:
&sigmatt+j = 1.79 +0.16-0.31 pb
AbstractThe first measurement of the cross section of t-tbar associated with an additional hard jet (t-tbar+jet) has been performed at CDF. The measurement is an important test of perturbative QCD, as NLO effects play an important role in the calculation of the theoretical cross section. In addition, most top events at the LHC will be produced with additional jets, and therefore this process is a substantial background for many new physics signals. The measurement is performed using b-tagged events in the lepton plus jets channel. A data-driven approach is used to predict the background content, and a 2D likelihood is formed to simultaneously measure the t-tbar+jet and tt without jet cross sections. The measured result is &sigmatt+j = 1.6 ± 0.2stat ± 0.5syst pb, which is in agreement with the standard model prediction &sigmatt+j = 1.79 +0.16-0.31 pb [1]. |
Result The measured t-tbar + jet cross section in the lepton plus jets channel using 4.1 fb-1 of CDF collected data is: &sigmatt+j = 1.6 ± 0.2stat ± 0.5syst pbWhich is in agreement with the standard model prediction [1]:
|
Plots & Tables |
 |
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 > 220 GeV, and MET > 20 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 > 220 GeV, and MET > 20 GeV. |
 |
The simultaneously measured tt+j and tt+0j cross-sections and statistical uncertainties are derived from a 2D likelihood fit. This is a plot of the 68% and 95% CL contours. |
 |
Systematic uncertainties on the measured tt+j cross-section. |
 |
Systematic uncertainties on the measured tt without jet cross-section. |
 |
Scalar sum of the transverse energy in the detector (Ht) for events with 1 high Pt lepton, at least 3 jets ( >=1 b-tagged ), MET > 20 GeV. We place a cut on Ht at 220 GeV to reduce background contribution. |
 |
Missing Transverse Energy in the detector. |
 |
The fifth lowest jet Et for events with five jets or more. These events are dominated by tt+j and the fifth jet is often from initial or final state radiation from the top pair. |
 |
The fifth lowest jet Eta for events with five jets or more. These events are dominated by tt+j and the fifth jet is often from initial or final state radiation from the top pair. |