Physics of the top quark at D0: New measurement of the production cross-section and mass

We present a measurement of the t{anti t} production cross section in p{anti p} collisions at {radical}s = 1.8 TeV and a measurement of top quark mass m{sub t} by the D0 experiment at the Fermilab Tevatron. The measurements are based on the data from the 1992- 1996 run during which the D0 detector was exposed to the integrated luminosity of approximately 125 pb{sup -1}. We observe 39 t{anti t} candidate events in the dilepton and lepton+jets decay channels with an expected background of 13.7 {+-} 2.2 events. We measure the top quark mass m{sub t} using a two constraint fit to m{sub t} in t{anti t} {yields} bW{sup +} {anti b}W{sup -} final states with one W decaying to q{anti q} and the other to e{nu} or {mu}{nu}. Events are binned in the fit mass versus a measure of probability for events to be the signal rather than a background. Likelihood fits to the data yield m{sub t} = 173.3 {+-} 5.6 (stat) {+-} 6.2 (syst) GeV/c{sup 2}. For this mass we measure the t{anti t} production cross section to be 5.5 {+-} 1.8 pb.