Top Mass Distributions

Contents

This likelihood method is the same one used in 1-D top mass analysis. The fit function consists of a Gamma and two Gaussian probability density function whose parameters are linearly depended on the top width.

  1. Generator-Level
    • Top Mass Distributions
    • Top Mass and Anti-Top Mass Difference
    • Top Mass Distributions after the event selection cuts
    • Top Mass and Anti-Top Mass Difference after the event selection cuts
  2. After Detector Simulation and Top Mass Reconstruction
    • 2tag: Top Mass Distributions without background
    • 2tag: Top Mass Distributions with wbb2p background with and without chi2 cut
    • 1tagT: Top Mass Distributions with wbb2p background with and without chi2 cut
    • Comparisons of 2tag and 1tagT samples

  1. Generator Level Studies


  2. Studies Using the Kinematic Fitter

    We use the kinematic chi2 fitter used in the Top Mass Template Method. This template method has been used at the CDF since run-I, and it is a well established, standard chi^2 minimalization technique used in the top quark mass measurement. This template method is described in detail in cite{prd}.
    In the template method, the four leading jets are assumed to correspond to the four partons from the ttbar decay chain to reconstruct a top mass. In the chi^2 fitter used in the template method, both sets of W decay daughters are constrained to have the invariant mass of the W boson, and both Wb states are constrained to have the same mass. This implies that the W mass have a significant effect on the chi^2 values. The ambiguity arising from the different ways of assigning the jets to the four quarks is resolved by selecting the assignment with the lowest chi^2, taking into account the b-tagging information. We perform a chi^2 minimization to fit the parton momenta from the ttbar daughters. Furthermore, we constrain m_{t} and m_{tbar} to be the same within the decay width of 1.5 GeV, produing one m_{t}^{reco} for each event.
    Furthermore, by applying a chi^2 cut, we can select events with low chi^2 values, and consequently events where the mass of t and tbar are close. However, we lose information of events with large mass difference between ttbar with this chi^2 cut.

  3. 2 Tag Samples After Simulation and Reconstruction
    1. Top Mass Distributions: Without background, without chi2 cut
    2. Hepg_top

    3. Top mass distributions and mean and rms values: With background, without chi2 cut
    4. On the left is the top mass distributions consisting of signal (yellow) and wbb2p background(blue). The right plots are mean and rms of the distributions as functions of top width. The red lines indicate the values from signal distribution and the blue lines indicate the values from signal and background added.

      Hepg_top
      Hepg_top

    5. Top mass distributions and mean and rms values: With background, with chi2 < 9.
    6. Hepg_top
      Hepg_top

    7. 1 Tag Tight Samples with Simulation and Reconstruction

      1. With background, without chi2 cut
        Hepg_top
        Hepg_top

      2. With background, with chi2<9
        Hepg_top
        Hepg_top

    8. Comparision of 2tag and 1tagT events

      1. With background, without chi2
        Hepg_top
        '
        Hepg_top

      2. With background, with chi2 < 9
        Hepg_top
        Hepg_top