A Measurement of the t anti-t Cross Section in p anti-p Collisions at s**(1/2) = 1.96-TeV using Dilepton Events with a Lepton plus Track Selection

This paper reports a measurement of the cross section for the pair productionof top quarksin p{bar p} collisions at {radical}s = 1.96 TeV at the Fermilab Tevatron. The data was collected from the CDF II detector in a set of runs with a total integrated luminosity of 1.1 fb{sup -1}. The cross section is measured in the dilepton channel, the subset of t{bar t} events in which both top quarksdecay through t {yields} Wb {yields} {ell}{nu}b, where {ell} = e, {mu}, or {tau}. The lepton pair is reconstructed as one identified electron or muon and one isolated track. The use of an isolated track to identify the second lepton increases the t{bar t} acceptance, particularly for the case in which one W decays as W {yields} {tau}{nu}. The purity of the sample may be further improved at the cost of a reduction in the number of signal events, by requiring an identified b-jet. They present the results of measurements performed with and without the request of an identified b-jet. the former is the first published CDF result for which a b-jet requirement is added to the dilepton selection. In the CDF data there are 129 pretag leptonmore » + track candidate events, of which 69 are tagged. With the tagging information, the sample is divided into tagged and untagged sub-samples, and a combined cross section is calculated by maximizing a likelihood. The result is {sigma}{sub t{bar t}} = 9.6 {+-} 1.2(stat.){sub -0.5}{sup +0.6}(sys.) {+-} 0.6(lum.) pb, assuming a branching ratio of BR(W {yields} {ell}{nu}) = 10.8% and a top mass of m{sub t} = 175 GeV/c{sup 2}.« less