ATLAS

Abstract:

We report on a search for pair production of a fourth generation charge -1/3 quark (b’) in pp collisions at s = 1.8 TeV by the DØ experiment at the Fermilab Tevatron using an integrated luminosity of 93 pb-1. Both b’ quarks are assumed to decay via flavor changing neutral currents (FCNC). The search uses the signatures γ + 3 jets + μ-tag and 2γ + 2 jets. We see no significant excess of events over the expected background. We place an upper limit on the production cross section times branching fraction that is well below theoretical expectations for a b’ decaying exclusively via FCNC for b’ masses up to mz + mb. © 1996 American Physical Society.

Abstract:

This Letter describes a direct search for charged Higgs boson production in proton-antiproton collisions at sqrt(s)=1.8 TeV recorded by the Collider Detector at Fermilab. Two-Higgs-doublet extensions to the standard model predict the existence of charged Higgs bosons. In such models, the branching fraction for top quarks B(t → H b → tau nu b) can be large. This search uses the hadronic decays of the tau lepton in this channel to significantly extend previous limits on charged Higgs production. © 1997 The American Physical Society.

Abstract:

A search for new physics has been carried out in the channel pp → γγ + ET, as expected in various supersymmetric models. We require two photons with transverse energy E^γT > 12 GeV and pseudorapidity |η^γ < 1.1. The distribution of missing transverse energy (ET) is consistent with background and no events have ET > 25 GeV. We set limits on production cross sections for selectron, sneutrino, and neutralino pairs, decaying into photons, which range from about 400 fb to 1 pb depending on the sparticle masses. A general limit of 185 fb (95% C.L.) is set on σ(pp → γγET + X), where e^γT > 12 GeV, |η^γ| < 1.1, and ET > 25 GeV. © 1997 The American Physical Society.

Abstract:

We present the results of a search for first generation scalar leptoquarks pairs (S1S®1) in 110 ± 7 pb⁻¹ of data collected by the Collider Detector at Fermilab. We assume both leptoquarks decay to an electron and a quark. Three candidate events, with masses below 140 GeV/c² and consistent with background expectations, are observed. We obtain a 95% confidence level upper limit on the production cross section as a function of the leptoquark mass. Using a next-to-leading order calculation of S1S®1 production, we exclude scalar leptoquarks with mass less than 213GeV/c² at 95% C.L. for a branching ratio into eq equal to 1. © 1997 American Physical Society.

Abstract:

We report on a search for supersymmetric squark and gluino particles in a data sample of 19 [Formula presented] of [Formula presented] collisions at [Formula presented] TeV recorded by the Collider Detector at Fermilab. We searched for events containing jets plus appreciable missing transverse energy [Formula presented] This signature is indicative of pair production and subsequent decay of squarks and/or gluinos. After all cuts, there are [Formula presented] events with [Formula presented] GeV and three jets, and [Formula presented] events with [Formula presented] GeV and four jets. These numbers of events are consistent with estimates of standard model processes plus detector-induced background sources. The analysis yields lower limits on gluino and squark masses, based on the predictions from the mnimal supersymmetric extension of the standard model. At the [Formula presented] confidence level, we find gluino and squark mass limits up to 216 [Formula presented] assuming equal gluino and squark masses, and gluino mass limits up to [Formula presented] [Formula presented] independent of squark mass. © 1997 The American Physical Society.