CDF evidence for the Top quark: detector issues

Abstract

We present the results of a search for the top quark in 19.3 pb −1 of pp̄ collisions at √3=1.8 TeV. The data were collected at the Fermilab Tevatron Collider using the Collider Detector at Fermilab (CDF) during the 1992/93 data taking period.The CDF detector has been significantly improved for this run, a silicon vertex detector (SVX) was added to allow identification of secondary vertices from b-decay, the muon system has been upgraded and the electron signature has been inproved. The analysis presented here assumes Standard Model decays of the top quark; in this framework a rather clean signal is expected in the final states with 2 high p t leptons ( e or μ ) and E T , or one high p t lepton, E T and jets with at least one of the jets identified as a b-quark. Two events are found in the dilepton final state with an estimated background of 0.56 −0.13 +0.25 . In the lepton plus jet final state, b-quarks are tagged either by identifying a secondary decay vertex, or a lepton ( e or μ ) consistent with the semileptonic decay of the b-quark or its cascade c-quark. Using the first b-tagging technique six events are found with a background of 2.3±0.3, while using the second we find seven events with a background of 3.1±0.3. We estimate the probability that the combined yield is consistent with a background fluctuation to be 0.26%. While the statistics is still too limited to firmly establish the existence of the top quark, the most natural interpretation is that this excess is due to t̄ production.