Update of the measurement of the t tbar cross section at √s =1.96 TeV

A measurement of the t(bar t) cross section at √s = 1.96 TeV is carried out on a data sample of ∼100 pb-1 in the dilepton and lepton+jets channels. Overall, 46 events are observed, with an expected background of 23.7 ± 3.0. The t(bar t) production cross section is measured to be: σpbar p yieldstbar t = 8.1 -2.0+2.2 (stat) -1.3+1.6 (sys) ± 0.8 (lumi) pb. The preliminary measurement of the t(bar t) cross section at a center-of-mass energy of 1.96 TeV presented at the 2003 winter conferences [1] is updated with improved object identification algorithms and a larger data sample of approximately 100 pb-1. The analyses reported herein are based on data sets taken from August 2002, until July 2003, where ∼190 pb-1 were delivered to the experiment and ∼130 pb-1 were recorded and reconstructed. As the various analysis channels have different trigger criteria and quality requirements, the integrated luminosity corresponding to each channel varies. The trigger requirements are the same as those reported in [1]. The run data quality requirements that were applied in [1] are also applied to this larger dataset and are supplemented by additional data quality requirements based on smaller units of data called luminosity blocks (∼1 minute of data taking). These requirements reduce the effective data sample by 6%. The most prominent change in the analyses occurred in the identification of electrons, where a likelihood is now used to combine individual criteria, such as electromagnetic cluster x2 [1], spatial track matching, the E/p matching [1], the fraction of electromagnetic energy of the cluster [1], the distance of closest approach to the primary vertex (DCA) used to select primary high transverse momentum electrons originating from the primary interaction vertex, and the isolation with respect to nearby tracks. A reduction of a factor two in the background is obtained using a likelihood based selection. To further remove the heavy flavor multijet background in the analyses involving primary muons, a simple cut on the DCA is also applied