A Measurement of the t-tbar Cross Section in p-pbar Collisions at √s = 1.96 TeV using Dilepton Events with a Lepton plus Track Selection

This paper reports a measurement of the cross section for the pair production of top quarks in ppbar collisions at √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^-1. The cross section is measured in the dilepton channel, the subset of t-tbar events in which both top quarks decay through t → Wb → lνb where l = e, μ, or τ. 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-tbar acceptance, particularly for the case in which one W decays as W → τν. 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. We 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 lepton + 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 σ(t-tbar) = 9.6 ± 1.2 (stat.) -0.5 +0.6 (sys.) ± 0.6 (lum.) pb, assuming a branching ratio of BR(W → lν) = 10.8% and a top mass of m_t = 175 GeV/c².