- Comparison of MC samples with and without the lepton filter. We use the lepton filter in our analysis.
These overlayed top mass distributions show that the effect of lepton filter is very small.
- Top Mass Distribution
Following histograms are the distributions of the top mass at the generator-level corresponding to various width. The top mass distribution falls off at 80 GeV/c^2 because the kinematic algoithm requires the invariant top mass to be greater than the sum of the invariant masses of two W bosons and the two b quarks, ensuring the top's decay to real W bosons. Moreover, the mean of the top mass shifts toward lower mass as the width increases due to the parton distribution function of ppbar. Since it is less likely to create partons with such a high energy that the probability of top mass being very large is small. So if there were no cut off at 80 GeV/c^2, the top mass distribution would have a longer tail at the lower energy and shifts the mean toward the lower side as the top width increases. In other words, the higher probability for smaller energy of ppbar results in a higher probability for light top quark production than heavy top quark produciton.
- Top Mass Difference at the generator level
- Top Mass Distribution after the selection cuts
These are the top mass samples that pass the event selection cuts in the massAna fitter.
- Top Mass Difference after the selection cuts
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.
- Top Mass Distributions: Without background, without chi2 cut
- Top mass distributions and mean and rms values: With background, without chi2 cut
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.
- Top mass distributions and mean and rms values: With background, with chi2 < 9.
- 1 Tag Tight Samples with Simulation and Reconstruction
- With background, without chi2 cut
- With background, with chi2<9
- With background, without chi2 cut
- Comparision of 2tag and 1tagT events
- With background, without chi2
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- With background, with chi2 < 9
- With background, without chi2