Kinematic Evidence For Top-quark Pair Production In W Plus Multijet Events In P(p)over-bar Collisions At Root-s=1.8 Tev

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. © 1995 The American Physical Societ

Properties of jets in Z boson events from 1.8 TeV p\u304p collisions

We present a study of events with Z bosons and hadronic jets produced in p\uafp collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 Z\u2192e+e 12 decays from 106pb 121 of integrated luminosity collected using the CDF detector at the Fermilab Tevatron Collider. The Z+ 65n jet cross sections and jet production properties have been measured for n=1 to 4. The data are compared to predictions of leading-order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation

Inclusive jet cross section in p\u304p collisions at 1as = 1.8 TeV

The inclusive jet differential cross section has been measured for jet transverse energies, ET, from 15 to 440 GeV, in the pseudorapidity region 0.1 64|\u3b7| 640.7. The results are based on 19.5pb 121 of data collected by the CDF Collaboration at the Fermilab Tevatron collider. The data are compared with QCD predictions for various sets of parton distribution functions. The cross section for jets with ET>200GeV is significantly higher than current predictions based on O(\u3b13s) perturbative QCD calculations. Various possible explanations for the high- ET excess are discussed

Search for the supersymmetric partner of the top quark in pp\u304 collisions at 1as=1.8 TeV

We report on a search for the supersymmetric partner of the top quark (top squark) produced in tt\u304 events using 110 pb-1 of pp\u304 collisions at 1as = 1.8 TeV recorded with the Collider Detector at Fermilab. In the case of a light top squark, the decay of the top quark into a top squark plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with standard model tt\u304 production and decay. Hence, we set limits on the branching ratio of the top quark decaying into a top squark plus LSP, excluding branching ratios above 45% for a LSP mass up to 40 GeV/c2

Measurement of the \u3b3 + D*\ub1 cross section in p\u304p collisions at 1as = 1.8 TeV

We have measured the cross section of gamma + D-*+/- production in <(p)over bar p> collisions at root s = 1.8 TeV using the Collider Detector at Fermilab. In this kinematic region, the Compton scattering process (g(c) --> gamma(c)) is expected to dominate and thus provide a direct link to the charm quark density in the proton. From the 45 +/- 18 gamma + D-*+/- candidates in a 16.4 pb(-1) data sample, we have determined the production cross section to be 0.38 +/- 0.15(stat) +/- 0.11(syst) nb for the rapidity range y(D-*+/-) < 1.2 and y(gamma) < 0.9, and for the transverse momentum range p(T)(D-*+/-) > 6 GeV/c and 16 < p(T)(gamma) < 40 GeV/c. The measured cross section is compared to a theoretical prediction