Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV

We present a measurement of the top quark pair production cross section in p (p) over bar collisions at root s=1.96 TeV using 318 pb(-1) of data collected with the Collider Detector at Fermilab. We select t (t) over bar decays into the final states e nu+jets and mu nu+jets, in which at least one b quark from the t-quark decays is identified using a secondary vertex-finding algorithm. Assuming a top quark mass of 178 GeV/c(2), we measure a cross section of 8.7 +/- 0.9(stat)(-0.9)(+1.1)(syst) pb. We also report the first observation of t (t) over bar with significance greater than 5 sigma in the subsample in which both b quarks are identified, corresponding to a cross section of 10.1(-1.4)(+1.6)(stat)(-1.3)(+2.0)(syst) pb.