Combination of Top Pair Production Cross Section Results

Combination of Top Pair Production Cross Section Results

Conference note 8148
Previous combinations

Combination of latest preliminary measurements up to 760/pb

We combine the latest results using up to 760 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,
lepton+jets channel with at least one soft muon b-tag Phys. Rev. D 72, 032002 (2005)
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 use the BLUE method [1,2,3], where we account for statistical and systematic correlations between the results. In case of asymmetric uncertainties, we take the average of the positive and negative uncertainties.

We find the top pair production cross section to be:

7.32 +-0.47(stat) +-0.57(syst)+-0.42(lumi) pb = 7.3+- 0.9 pb when we assume a top quark mass of 175 GeV
7.4 +- 0.9 pb when we assume a top quark mass of 172.7 GeV (Summer 2005 CDF+D0 Run I+II average)
7.5 +- 0.9 pb when we assume a top quark mass of 172.0 GeV (CDF March 2006 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 (+- 2.7 GeV) around the CDF average for the top quark mass. eps
	Combination of Preliminary Results compared to theoretical predictions[4,5] as a function of sqrt{s}. A top quark mass value of 175 GeV is assumed. eps

References

[1] L.Lyons, D.Gibaut and P.Clifford, NIM A270, 110-117 (1988).
[2] L.Lyons, A.Martin and D.Saxon, Phys. Rev. D 41, 3 (1990).
[3]A.Valassi, NIM A500, 391 (2003).
[4] M.Cacciari, S.Frixione, G.Ridolfi, M.Mangano and P.Nason, JHEP 404, 68 (2004)
[5]N.Kidonakis and R.Vogt, Phys. Rev. D 68, 114014 (2003).

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