Combination of preliminary measurements up to 350/pb

We combine the latest results using up to 350 pb-1 of data from :

• dilepton channel
• lepton+jets channel with an artificial neural network,
• lepton+jets channel with at least one secondary vertex b-tag,
• MET+jets with at least one secondary vertex b-tag, where the lepton is not required to be identified,
• all-hadronic channel with at least one secondary vertex b-tag

We find the top pair production cross section to be:

7.1 +- 1.0 pb when we assume a top quark mass of 175 GeV
7.3 +- 1.1 pb when we assume a top quark mass of 172.7 GeV (latest CDF+D0 Run I+II average)

Note the acceptance of all the event selections decreases with decreasing top mass, due to the lower energies of the top decay products. Therefore the measured cross section increases as the assumed top mass decreases, since the cross section is estimated as the number of observed candidates minus the estimated background, all divided by the acceptance and integrated luminosity of the data sample.

	Combination of Preliminary Results, when we assume a top quark mass of 175 GeV. eps (ghostview: Media menu, Display settings, Graphics Alpha to 1 to see cross-hatch)
	Combination of Preliminary Results compared to theoretical predictions[4,5] as a function of top quark mass. The slope of the almost-horizontal error bar indicates the dependence of the measured cross section on the top mass over a range of +- 1 standard deviations (+- 2.9 GeV) around the world average for the top quark mass. eps

Combination of 5 published measurements up to 200/pb

We combine the five published CDF results with up to 200 pb-1 of data from:

• Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV using Dilepton Events
  Phys. Rev. Lett. 93, 142001 (2004)
• Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV using Lepton + Jets Events with Secondary Vertex b-tagging
  Phys. Rev. D71, 052003 (2005)
• Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV using Kinematic Fitting of b-tagged Lepton + Jet Events
  Phys. Rev. D71, 072005 (2005)
• Measurement of the ttbar Production Cross Section in ppbar Collisions using the Kinematics of Lepton+Jet Events
  hep-ex/0504053 Phys. Rev. D, accepted August 2005
• Measurement of the tt-bar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV Using Lepton Plus Jets Events with Semileptonic B Decays to Muons
  Phys. Rev. D 72, 032002 (2005)

We find the top pair production cross section to be:

6.0 +- 1.2 pb when we assume a top quark mass of 175 GeV
6.1 +- 1.2 pb when we assume a top quark mass of 172.7 GeV (latest CDF+D0 Run I+II average)

Note the acceptance of all the event selections decreases with decreasing top mass, due to the lower energies of the top decay products. Therefore the measured cross section increases as the assumed top mass decreases, since the cross section is estimated as the number of observed candidates minus the estimated background, all divided by the acceptance and integrated luminosity of the data sample.

	Combination of CDF Published Results, when we assume a top quark mass of 175 GeV. eps (ghostview: Media menu, Display settings, Graphics Alpha to 1 to see cross-hatch)
	Combination of CDF Published Results compared to theoretical predictions[4,5] as a function of top quark mass. The slope of the almost-horizontal error bar indicates the dependence of the measured cross section on the top mass over a range of +- 1 standard deviations (+- 2.9 GeV) around the world average for the top quark mass. eps

References

Questions? Contact us!
Evelyn Thomson (University of Pennsylvania,
Charles Plager (University of California at Los Angeles),
Richard Huges (The Ohio State University)