Measurement of top quark top antiquark production cross section and search for new physics beyond the standard model.

Abstract

We present a measurement of the tt production cross section in pp collisions at $\sqrt{s}=1.8$ TeV by the DO experiment at the Fermilab Tevatron. We observe 40 tt candidate events in single and dilepton decay channels with an expected background of 13.3 $\pm$ 2.2 events. For a top quark mass of 172 GeV/c$\sp2,$ we measure the ttbar production cross section to be 5.9 $\pm$ 1.8 pb. We have also performed a search for inclusive energetic diphoton events with large missing transverse energy at DO Such events are expected from pair production of charginos and neutralinos within the framework of the minimal supersymmetric standard model with a light gravitino. No excess of events is observed. A 95% CL exclusion region in the supersymmetry parameter space is presented. Lower mass bounds of 150 GeV/c$\sp2$ for the lightest chargino and 77 GeV/c$\sp2$ for the lightest neutralino are derived. Both the measurements are based on data from an integrated luminosity of approximately 106 pb$\sp{-1}$ accumulated during the 1992-1996 collider run.