Observation of the top quark

Summary

The D0 Collaboration reports on a search for the Standard Model top quark in p$\bar p$ collisions at √s=1.8 TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50 pb⁻¹. We have searched for t$\bar t$ production in the dilepton and single-lepton decay channels, with and without tagging of b quark jets. We observe 17 events with an expected background of 3.8±0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2·10⁻⁶ (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top-quark decay. We conclude that we have observed the top quark and measure its mass to be 199 ⁺¹⁹₋₂₁ (stat)±22(syst) GeV/c² and its production cross-section to be (6.4±2.2) pb.