Study of the $t\bar{t}$ in the dilepton channel at $\sqrt{s} = 1.96$ TeV with the Collider Detector at Fermilab

Abstract

This study presents new measurement of the top quark mass in the t$\bar{t}$ to the dilepton decay channel. It is based on the observed linear dependence of the top mass to the transverse momentum PT of the leptons that are two of the fi products of the top-antitop pair decay. It uses data collected by the CDF detector from December 2004 to March 2007 that correspond to an integrated luminosity of 1.8 fb-1 .Two independent and mutually compatible methods have been implemented for this reason, both depending on the leptons’ PT. The final method, called the ”Straight Line”, exploits just the linear relation between the leptons’ PT and the top mass. With the second one, called the ”Likelihood”, the full PT spectrum is modeled by an analytical function and the top mass is estimated using the likelihood minimization procedure. A top quark mass of mtop=156±20(stat)±4.6(syst) GeV/c2 is obtained with the Likelihood method and of 149±21(stat)±5.0(syst) GeV/c2 is obtained with the Straight Line one.This study is complementary to other CDF mass studies in the dilepton channel. It differs by the fact that is not dependent on the jets and does not use the b quark secondary vertex b-tagging technique. It is therefore not dependent on the jet energy scale uncertainty that is at this moment the biggest systematic contribution to all other methods. This method is a simple and straightforward method that aims to a small systematic uncertainty. The statistical uncertainty is still not competitive with respect to the other methods, due to the relatively small sensitivity of the leptons' PT to the top mass. On the other hand, this study is a very good preview of the method with the upcoming LHC data, where the statistical error is expected to be greatly suppressed. The dominating error will then be the systematic one and this method promises to be competitive or even better, regarding this point, with respect to the other methods.