(FNAL)

(Rutgers)

The top quark, with a mass of about 175 GeV, has an expected lifetime of approx 0.5 x 10

This sample is composed mainly of three processes: ttbar produced via gluon-fusion, ttbar produced via quark annihilation, and background from the W boson produced in association with other quarks. Top quark events have b quarks in the decay. CDF has a method to identify the b quarks called tagging, and we split our sample into subsamples of 1 tag and 2 tags.

To obtain our result, we created a large number of simulated data samples with the varying fractions of gg produce top events. These simulated samples, or "pseudo-experiments" as we call them, are then fit to the neural network templates. We then use a statistical method called Feldman-Cousins (FC) to create a map from the fitted value of our pseudo-experiments to the real gg production fraction. More info on Feldman-Cousins Method can be found here.

Like any measurement there are sources of uncertainty. In our case our main source of uncertainty comes from statistics, we don't have a large number of ttbar events. Other sources of uncertainty come from systematics, which are uncertainties based on our experimental method. Systematics that we consider are: how well do we measure the energy of the decay products of the top, how well do we model the initial state and final state radiation in our simulation, how well do we know the background shape and composition, and how well our simulation models more complicated ways of producing top events (so call next to leading order (NLO) processes).

## These are FC bands. The true gg fractions (Y axis) Vs a quantity obtained from the NN fit (X axis). The red line indicated the NN
fit obtained from data, and its intersection with the green band indicates the 68% confidence level limit. The intersection with
the blue line indicates the 68% confidence level limit if we
were not affected by systematics. (EPS) |
---|

## Here you can see the 68% confidence level limit and the 95%
confidence level limit. (EPS) |
---|

## Here is the fit of to the neural network for the 1 tag events. (EPS) |
## Here is the fit of to the neural network for the 2 tag events. (EPS) |
---|

- Statistical Uncertainty Only: C
_{f}^{true}< 0.23 at 68% confidence level limit. - All Uncertainties: C
_{f}^{true}< 0.33 at 68% confidence level limit, and C_{f}^{true}< 0.61 at 95% confidence level limit

- A more complete description of the analysis method can be found here.
- Our previous result with 695 pb
^{-1}can be found here.

Jared Yamaoka Last modified: Thurs May 17 11:56:50 CST 2007