ttbar Production Cross-Section Ratio and Limits on Non-Standard Model Deacys of Top
Ken Bloom and Monica Tecchio
University of Michigan

Winter 2004 results with ~125 pb^-1
R&sigma = 1.45+0.83-0.55
R&sigma > 0.46 at 95% CL
R&sigma < 4.45 at 95% CL
&beta < 0.46 at 95% CL
&beta' < 0.47 at 95% CL

Measuring the ttbar cross section establishes that we can find top. But how do we know that the "top" that we observe in the dilepton decay mode is the same "top" that we observe in the lepton plus jets mode? If both are top, they should have the same production cross section. Thus, we measure R&sigma = &sigmall/&sigmalj. In taking the ratio, we are careful to handle the small statistics, and to cancel the systematic uncertainties that are correlated between the two analyses.
In addition, the cross-section measurements assume that top decays with standard-model branching fractions, e.g. there is virtually always a W in the decay, which decays with its usual branching fractions. If this is not true, then our measured value for R&sigma would not be consistent with unity. Thus, one can use R&sigma to extract limits on non-standard branching fractions of top. These limits are by necessity model-dependent. We use a simple model which does not have any particular physics motivation, but should give a reasonable estimate of the efficiency to detect the non-standard decay.

  • Documentation
    CDF 6714

  • Presentations
    Status report, top meeting, October 2, 2003
    Preblessing, top meeting, February 19, 2004
    Blessing, top meeting, March 4, 2004

  • Blessed figures and tables

    • Description gif eps
    Probability distribution function for the ratio that we observe in the data. eps
    Probability distribution for the ratio of lepton plus jets to dilepton acceptances. Red is if you fail to cancel uncertainties that are correlated between the two acceptance estimates, green is if you do cancel them. There is an obvious improvement if you do the cancellation (but with our current statistics, it has no impact on the result). eps
    Expected lower limits on beta (branching fraction to an all-hadronic decaying top) as a function of integrated luminosity. See the note for a description of the models. eps
    Expected lower limits on beta-prime (branching fraction to an all-leptonic decaying top) as a function of integrated luminosity. See the note for a description of the models. eps
  • Correspondence
    Tony Liss thinks we got the various factors of 2 and B correct