We summarize a search for the top quark with the Collider Detector at Fermilab (CDF) in a sample of Pp collisions at Js =1.8 TeV with an integrated luminosity of 19.3 pb . We find 12 events consistent with either two 8' bosons, or a 8' boson and at least one b jet. The probability that the measured yield is consistent with the background is 0.26%. Though the statistics are too limited to establish firmly the existence of the top quark, a natural interpretation of the excess is that it is due to tt production.Under this assumption, constrained fits to individual events yield a top quark mass of 174+ 10 -)) GeV/c . The tt production cross section is measured to be 13.9 -+)II pb. PACS numbers: 14.65.Ha, 13.85.Ni, 13.85.gk The standard model has enjoyed outstanding success, yet the top quark, which is required as the weak-isospin partner of the bottom quark, has remained unobserved. Direct searches at the Fermilab Tevatron have placed a 95%%uo confidence level lower limit of M&,~& 131 GeV/c [1]. Global fits to precision electroweak measurements yield a favored mass of M&,~= 177-+|I+ -I9 GeV/c [2]. One expects that, at Tevatron energies, most top quarks are produced in pairs. For M,o&~85 GeV/c, each top quark decays to a real 8' boson and a b quark.The observed event topology is then determined by the decay mode of the two H bosons. About 5k of the time 226 VOLUME 73, NUMBER 2 PHYSICAL REVIEW LETTERS 11 JULY 1994 both W bosons decay to ev or p v (the "dilepton mode"), giving two high-P~leptons with opposite charge, two b jets, and large missing transverse energy (k"7. ) from the undetected neutrinos [3]. In another 30% of the cases one W boson decays to ev or p v, and the other to a qq' pair (the "lepton+jets mode"). This final state includes a high-Pz charged lepton, k"z, and jets from the 8' and the two b quarks. The remaining 65% of the final states involve the hadronic decays of both W bosons, or the decay of one or both of the 8'bosons into r leptons. These channels have larger backgrounds and are not considered here. This analysis is based on a sample of pp collisions at vs =1. 8 TeV with an integrated luminosity of 19.3

We present a study of W +multijet events that compares the kinematics of the observed events with expectations from direct QCD W +jet production and from production and decay of top quark pairs. The data were collected in the 1992-93 run with the Collider Detector at Fermilab (CDF) from 19.3 pb −1 of proton-antiproton collisions at √ s = 1.8 TeV. A W + ≥ 2 jet sample and a W + ≥ 3 jet sample are selected with the requirement that at least the two or three jets have energy transverse with respect to the beam axis in excess of 20 GeV. The jet energy distributions for the W + ≥ 2 jet sample agree well with the predictions of direct QCD W production. From the W + ≥ 3 jet events, a "signal sample" with an improved ratio of tt to QCD produced W events is selected by requiring each jet to be emitted centrally in the event center of mass frame.This sample contains 14 events with unusually hard jet E T distributions not well described by expectations for jets from direct QCD W production and other background processes. Using expected jet E T distributions, a relative likelihood is defined and used to determine if an event is more consistent with the decay of tt pairs, with M top = 170GeV/c 2 , than with direct QCD W production. Eight of the 14 signal sample events are found to be more consistent with top than direct QCD W production, while only 1.7 such top-like events are expected in the absence of tt. The probability that the observation is due to an upward fluctuation of the number of background events is found to be 0.8%. The robustness of the result was tested by varying the cuts defining the signal sample, and the largest probability for such a fluctuation found was 1.9% . Good agreement in the jet spectra is obtained if jet production from tt pair decays is included.For those events kinematically more consistent with tt we find evidence for a b-quark content in their jets to the extent expected from top decay, and larger than expected for background processes. For events with four or more jets, the discrepancy with the predicted jet energy distributions from direct QCD W production, and the associated excess of b-quark content is more pronounced.

No abstract

We present a n analysis of data from pp collisions a t a center-of-mass energy of , , G = 1800 GeV. A measurement is made of the ratio R r u B ( p p + W + ev)/uB(pp -+ Z O + e e ) . The data represent 19.6 pb-' collected by the Collider Detector a t Fermilab during the 1992-1993 collider run of the Fermilab Tevatron. We find R = 10.90 * 0.32(stat)*O.Z9(syst), and from this value we extract a measurement of the W t ev branching ratio r ( W + e v ) / r ( W ) = 0.1094 dz 0.0033(stat)~0.0031(syst). From this branching ratio we set a limit on the top quark mass of mt > 62 ~e V / c ' a t the 95% confidence level. In contrast with direct searches for the top quark, this limit makes no assumptions about the allowed decay modes of the top quark. In addition, we use a calculation of the leptonic width r ( W + ev) to obtain a value for the W total decay width: P(W) = 2.064 0.060(stat)&O.O59(syst) GeV. PACS number(s): 13.38.-b, 12.15.Ff, 14.65.Ha, 14.70.-e

We have used a kinematic technique to distinguish top quark pair production from background in pp¯ collisions at √s=1.8 TeV, applied to 67 pb−1 of data. We define a sample of W+≥3 jet events in which the jets are produced at large angles relative to the incident beams. In this sample, we find an excess of events with large jet transverse energies relative to expectations from background. The excess is consistent with top quark production; a large fraction of events in this kinematic region contains b jets. We interpret these results as evidence that most of the selected events are from tt¯ decay