Search for charged Higgs decays of the top quark using hadronic tau decays

We present the result of a search for charged Higgs decays of the top quark, produced in $p\bar{p}$ collisions at $\surd s =$ 1.8 TeV. When the charged Higgs is heavy and decays to a tau lepton, which subsequently decays hadronically, the resulting events have a unique signature: large missing transverse energy and the low-charged-multiplicity tau. Data collected in the period 1992-1993 at the Collider Detector at Fermilab, corresponding to 18.7$\pm$0.7~pb$^{-1}$, exclude new regions of combined top quark and charged Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp; submitted to Phys. Rev.

Inclusive jet cross section in pˉp{\bar p p} collisions at s=1.8\sqrt{s}=1.8 TeV

The inclusive jet differential cross section has been measured for jet transverse energies, $E_T$, from 15 to 440 GeV, in the pseudorapidity region 0.1$\leq | \eta| \leq$0.7. The results are based on 19.5 pb$^{-1}$ 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 $E_T>200$ GeV is significantly higher than current predictions based on O($\alpha_s^3$) perturbative QCD calculations. Various possible explanations for the high-$E_T$ excess are discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review Letter

Measurement of Dijet Angular Distributions at CDF

We have used 106 pb^-1 of data collected in proton-antiproton collisions at sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular distributions in events with two jets in the final state. The angular distributions agree with next to leading order (NLO) predictions of Quantum Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at 95% confidence level (CL) a model of quark substructure in which only up and down quarks are composite and the contact interaction scale is Lambda_ud(+) < 1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6 TeV.Comment: 16 pages, 2 figures, 2 tables, LaTex, using epsf.sty. Submitted to Physical Review Letters on September 17, 1996. Postscript file of full paper available at http://www-cdf.fnal.gov/physics/pub96/cdf3773_dijet_angle_prl.p

Ratios of bottom meson branching fractions involving J/psi mesons and determination of b quark fragmentation fractions

We report a measurement of the ratios of the decay rates of the B^+, B^0 and B^0_s mesons into exclusive final states containing a J/psi meson. The final states were selected from 19.6 pb^{-1} of p-pbar collisions recorded by the Collider Detector at Fermilab. These data are interpreted to determine the bquark fragmentation fractions f_u, f_d and f_s. We also determine the branching fractions for the decay modes B^+ --> J/psi K^+, B^+ --> J/psi K^*(892)^+, B^0 --> J/psi K^0, B^0 --> J/psi K^*(892)^0 and B_s^0 --> J/psi phi(1020). We discuss the implications of these measurements to B meson decay models.Comment: 40 pages with 5 figures. Submitted to Phys. Rev. D. PostScript also available at http://www-cdf.fnal.gov/physics/pub96/cdf3609_bfrag_br_prd.p

Search for R-parity-violating supersymmetry in a final state containing leptons and many jets with the ATLAS experiment using s√=13 TeV proton–proton collision data

A search for R-parity-violating supersymmetry in final states characterized by high jet multiplicity, at least one isolated light lepton and either zero or at least three b-tagged jets is presented. The search uses 139fb−1 of s√=13 TeV proton–proton collision data collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature gluino production, top-squark production, or electroweakino production. The dominant sources of background are estimated using a data-driven model, based on observables at medium jet multiplicity, to predict the b-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. Machine-learning techniques are used to reach sensitivity to electroweakino production, extending the data-driven background estimation to the shape of the machine-learning discriminant. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted, reaching as high as 2.4 TeV in gluino mass, 1.35 TeV in top-squark mass, and 320 (365) GeV in higgsino (wino) mass

The SVX II silicon vertex detector upgrade at CDF

Precision tracking and vertex reconstruction play a crucial role in heavy flavor physics at CDF, in reconstructing the charm and beauty decay vertices in beauty and top events. A significant upgrade to the CDF detector, including a new silicon tracker, will support an extensive physics program with the high luminosity provided by the Main Injector accelerator upgrade. The specifications and design considerations for this new silicon tracker/vertex detector are discussed

Search for gluino and squark cascade decays at the Fermilab tevatron collider

We report on a search for supersymmetry using dilepton events which complements the classic missing E(T) plus multijet analyses. Using 19 pb(-1) of <p(p)over bar> collisions at root s = 1.8 TeV recorded with the Collider Detector at Fermilab we have searched for squarks and gluinos decaying into charginos and producing events with two leptons. We observe one candidate event. In comparison, the expected number of background events from standard model processes is 2.39 +/- 0.63(stat)(-0.42)(+0.77)(syst). Hence we set limits on gluino and squark production based on predictions from the supergravity inspired minimal supersymmetric extension of the standard model

Search for gluino and squark cascade decays at the Fermilab tevatron collider

We report on a search for supersymmetry using dilepton events which complements the classic missing E(T) plus multijet analyses. Using 19 pb(-1) of collisions at root s = 1.8 TeV recorded with the Collider Detector at Fermilab we have searched for squarks and gluinos decaying into charginos and producing events with two leptons. We observe one candidate event. In comparison, the expected number of background events from standard model processes is 2.39 +/- 0.63(stat)(-0.42)(+0.77)(syst). Hence we set limits on gluino and squark production based on predictions from the supergravity inspired minimal supersymmetric extension of the standard model

Properties of Jets in W Boson Events from 1.8 TeV ¯pp Collisions

We present a study of events with W bosons and hadronic jets produced in ¯pp collisions at a center of mass energy of 1.8 TeV. The data consist of 51 400 W±→e±ν decay candidates from 108pb−1 of integrated luminosity collected using the CDF detector at the Fermilab Tevatron Collider. Cross sections and jet production properties have been measured for W+≥1 to ≥4 jet events. The data are compared to predictions of leading-order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation

Search for flavor-changing neutral current B meson decays in p(p)over-bar collisions at root s=1.8 TeV

We report on a search for the flavor-changing neutral current decays B-d,s(0) --> mu(+)mu(-), B+ --> mu(+)mu(-)K(+), and B-0 --> mu(+)mu(-)K(*0) using data from collisions at root s = 1.8 TeV, collected with the Collider Detector at Fermilab during the 1992-1993 running period. We find no indication of such decays, and we set the following 90% confidence level upper limits on branching ratios: B(B-0 --> mu(+)mu(-)) mu(+)mu(-)) mu(+)mu(-)K(+)) mu(+)mu(-)K(*0)) < 2.5 x 10(-5)