Jeff Tseng

Abstract:

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.

Abstract:

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 tt̄ 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 ET distributions not well described by expectations for jets from direct QCD W production and other background processes. Using expected jet ET distributions, a relative likelihood is defined and used to determine if an event is more consistent with the decay of tt̄ pairs, with Mtop=170 GeV/c2, than with direct QCD W production. Eight of the 14 signal sample events are found to be more consistent with top-quark than direct QCD W production, while only 1.7 such top-quark-like events are expected in the absence of tt̄. 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 tt̄ pair decays is included. For those events kinematically more consistent with tt̄ we find evidence for a b-quark content in their jets to the extent expected from top quark decay, and larger than expected for background processes. For events with four or more jets, the discrepancy with the predicted jet distributions from direct QCD W production, and the associated excess of b-quark content, is more pronounced.

Abstract:

Direct limits are set on WWZ and WW three-boson couplings in a search for WW and WZ production with high transverse momentum in pp» collisions at s=1.8 TeV, using the Collider Detector at Fermilab. The results are in agreement with the SU(2) × U(1) model of electroweak interactions. Assuming standard model WW couplings, the limits are interpreted as direct evidence for a nonzero WWZ coupling at subprocess energies near 500 GeV. Alternatively, assuming identical WWZ and WW couplings, bounds -0.11< <2.27 and -0.81< <0.84 are obtained at 95% C.L. for a form factor scale 1000 GeV. © 1995 The American Physical Society.

Abstract:

We report limits on anomalous ZZ and Z couplings derived from an analysis of Z+photon production based upon approximately 20 pb-1 of the pp collision data recorded by the Collider Detector at Fermilab. We observe good agreement with the standard model expectation that all Z couplings are zero. Confidence level intervals for individual couplings and contours for pairs of CP-conserving/violating ZZ and Z couplings are presented. © 1995 The American Physical Society.

Abstract:

We report on a study of W + photon production in approximately 20 pb-1 of p-p collisions at s=1.8 TeV recorded with the Collider Detector at Fermilab. Our results are in good agreement with standard model expectations and are used to obtain limits on anomalous CP-conserving WW couplings of -2.3<<2.2 for =0 and -0.7<<0.7 for =0 at 95% C.L. We obtain the same limits for CP-violating couplings. These results provide limits on the higher-order electromagnetic moments of the W boson of 0.8

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