Combination of Top Pair Production Cross Section Results

Combination of Top Pair Production Cross Section Results

Conference note 9448

We combine five results using up to 2.8 fb-1 of data:

DIL dilepton channel (2.8 fb-1)
ANN lepton+jets channel with an artificial neural network (2.8 fb-1)
SVX lepton+jets channel with at least one secondary vertex b-tag (2.7 fb-1)
SLT-mu lepton+jets channel with at least one soft muon b-tag (2.0 fb-1)
SLT-e lepton+jets channel with at least one soft electron b-tag (1.7 fb-1)

We use the BLUE method (see conference note for references), 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 quark pair production cross section to be:
7.02 +-0.30(stat) +-0.38(syst)+-0.41(lumi) pb = 7.02+- 0.63 pb
where we assume a top quark mass of 175 GeV.
The relative uncertainty is 9%. The improvement in combining 5 measurements relative to the single best measurement (SVX) is 16%.

eps
Combination of Preliminary Results, when we assume a top quark mass of 175 GeV. For each measurement, the statistical uncertainty is shown by the magenta line, which is superimposed on the total uncertainty including systematic and luminosity uncertainties as shown by the blue line. We find excellent agreement with the theoretical prediction for a top quark mass of 175 GeV and centre-of-mass energy of 1.96 TeV of 6.73+0.71-0.79 pb from [1] using CTEQ6.5, 6.73+0.72-0.63 pb from [2] using CTEQ6.6, and 6.90+0.46-0.64 pb from [3] using CTEQ6.6. Note that the scale and PDF uncertainties have been added linearly here.

eps
Combination of Preliminary Results compared to theoretical predictions[1] as a function of sqrt{s}. A top quark mass value of 175 GeV is assumed. The predictions from [1] are shown to compare the predictions at different energies, top quark masses and PDF sets. Note that the predictions from [2] are quite similar, but are not shown here as otherwise this plot would become extremely busy. At sqrt(s)=1960 GeV, the central values of the predictions from [1] are shown at a top quark mass of 170 and 175 GeV for CTEQ6.5 and MSTW2006nnlo. The uncertainty (due to scale and PDF variations) of the 175 CTEQ6.5 prediction is shown by the filled blue region. At sqrt(s)=1800 GeV, the predictions use CTEQ6M and MRST 2002. At 1800 GeV, the predictions from the CTEQ and MRST have almost exactly the same central values.

eps
Combination of Preliminary Results compared to theoretical predictions[1,2,3] as a function of top quark mass. A top quark mass value of 175 GeV is assumed for the experimental result. The theoretical curves use CTEQ6.5 (Cacciari [1]) or CTEQ6.6 [2,3]. There are three curves for each theory, the middle curve shows the central prediction, while the upper and lower curves show the range of the prediction given scale and PDF uncertainties.

Reference [1] M.Cacciari, S. Frixione, G. Ridolfi, M. Mangano and P. Nason, arXiv:0804.2800; ibid, JHEP 404, 68 (2004).
Reference [2] N. Kidonakis and R. Vogt, arXiv:0805:3844 (2008); ibid, Phys. Rev. D 68, 114014 (2003).
Reference [3] S. Moch and P. Uwer, arXiv:0807.2794 and arXiv:0804.1476 (2008)
Previous combinations 2006 and 2005

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

	eps Combination of Preliminary Results, when we assume a top quark mass of 175 GeV. For each measurement, the statistical uncertainty is shown by the magenta line, which is superimposed on the total uncertainty including systematic and luminosity uncertainties as shown by the blue line. We find excellent agreement with the theoretical prediction for a top quark mass of 175 GeV and centre-of-mass energy of 1.96 TeV of 6.73+0.71-0.79 pb from [1] using CTEQ6.5, 6.73+0.72-0.63 pb from [2] using CTEQ6.6, and 6.90+0.46-0.64 pb from [3] using CTEQ6.6. Note that the scale and PDF uncertainties have been added linearly here.
	eps Combination of Preliminary Results compared to theoretical predictions[1] as a function of sqrt{s}. A top quark mass value of 175 GeV is assumed. The predictions from [1] are shown to compare the predictions at different energies, top quark masses and PDF sets. Note that the predictions from [2] are quite similar, but are not shown here as otherwise this plot would become extremely busy. At sqrt(s)=1960 GeV, the central values of the predictions from [1] are shown at a top quark mass of 170 and 175 GeV for CTEQ6.5 and MSTW2006nnlo. The uncertainty (due to scale and PDF variations) of the 175 CTEQ6.5 prediction is shown by the filled blue region. At sqrt(s)=1800 GeV, the predictions use CTEQ6M and MRST 2002. At 1800 GeV, the predictions from the CTEQ and MRST have almost exactly the same central values.
	eps Combination of Preliminary Results compared to theoretical predictions[1,2,3] as a function of top quark mass. A top quark mass value of 175 GeV is assumed for the experimental result. The theoretical curves use CTEQ6.5 (Cacciari [1]) or CTEQ6.6 [2,3]. There are three curves for each theory, the middle curve shows the central prediction, while the upper and lower curves show the range of the prediction given scale and PDF uncertainties.