A Measurement of the ttbar Production Cross Section Using Dileptons


Authors:

Monica Tecchio, Bo Jayatilaka, Dan Amidei
University of Michigan

Susana Cabrera
IFIC (CSIC-Univ de Valencia) -Visitor in CDF with Duke University

Daniel Whiteson
University of Pennsylvania

Tuula Maki
University of Helsinki and HIP

Yen-Chu Chen
Academia Sinica

Yuji Takeuchi, Naoki Kimura
University of Tsukuba

Fiodar Prakoshyn
JINR, Dubna

Veronique Boisvert
University of Rochester


Abstract
A measurement of the tt production cross section in pp collisions at sqrt{s} = 1.96 TeV using events with two leptons  is reported. The data were collected by the CDF II Detector. The preliminary result in a dataset corresponding to an integrated luminosity of 750 pb-1 is:  

8.3 ± 1.5(stat) ± 1.0(syst) ± 0.5(lumi)  pb.

where the first uncertainty is statistical, the second is the convolution of the acceptance and background systematics and the third comes the 6% uncertainty in the luminosity measurement.


Selection
See "Measurement of the tt Production Cross Section in pp Collisions at sqrt(s)=1.96 TeV Using Dilepton Events",Phys. Rev. Lett 93 ,142001 (2004) and CDF Public Conference Note


Results
The next table contains a summary of the background estimates for each jet bin after all cuts but the cut on HT and opposite sign lepton requirements are applied. The last column contains the candidate events with all cuts applied. The table also shows the total background, the tt expectations for a cross section of 6.7 pb, their sum (labeled ``Total SM expectations'') and the number of candidates events in 750 pb-1 of data.
Njet table

A breakdown of the dilepton content in candidate events for the different backgrounds, tt predictions and data is shown in the next table.
Dilepton flavor table

The next figure shows the number of candidate events in 0,1 and >=2 jet bins together with a histogram representing the components of the background.  The yellow band gives the tt contribution assuming the measured cross section of 8.3 pb. The red hatched area is the uncertainty in the total background estimate. A .eps version of the same plot.
Njet plot


In the following are plots of selected kinematic variables for the DIL candidate events. The data (black point) are superimposed to a colored histogram of background contributions, normalized according to the background summary table above. The top signal contribution is normalized to the measured cross section of 8.3 pb.
Transverse energy of both leptons in the event .eps Lepton Pt
Event missing transverse energy .eps MET
Dilepton invariant mass .eps Zmass
Event HT .eps HT