Search Results (118 total)

The beam-beam effects have been the dominating sources of beam loss and lifetime limitations in the Tevatron proton-antiproton collider [V. Shiltsev , Phys. Rev. ST Accel. Beams 8, 101001 (2005)]. Electron lenses were originally proposed for compensation of electromagnetic long-range and head-on beam-beam interactions of proton and antiproton beams [V. Shiltsev , Phys. Rev. ST Accel. Beams 2, 071001 (1999).]. Results of successful employment of two electron lenses built and installed in the Tevatron are reported by Shiltsev et al. [Phys. Rev. Lett. 99, 244801 (2007); New J. Phys. 10, 043042 (2008)] and by Zhang et al. [X.-L. Zhang , Phys. Rev. ST Accel. Beams 11, 051002 (2008)]. In this paper we present design features of the Tevatron electron lenses (TELs), discuss the generation of electron beams, describe different modes of operation, and outline the technical parameters of various subsystems.

We present the first measurement of associated direct photon+muon production in hadronic collisions, from a sample of 1.8 TeV pp̅ collisions recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily from the Compton scattering process cg→cγ, with the final state charm quark producing a muon. Hence this measurement is sensitive to the charm quark content of the proton. The measured cross section of 29±9 pb is compared to a leading-order QCD parton shower model as well as a next-to-leading-order QCD calculation.

We present the first measurement of the jet pseudorapidity distribution in direct photon events from a sample of pp̅ collisions at sqrt[s]=1.8 TeV, recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily from hard quark-gluon Compton scattering, qg→qγ, with the final state quark producing the jet of hadrons. The jet pseudorapidity distribution in this model is sensitive to parton momentum fractions between 0.015 and 0.15. We find that the shape of the measured pseudorapidity distribution agrees well with next-to-leading order QCD calculations.

We report a measurement of the ratios of the decay rates of the B⁺, B⁰, and B_s⁰ mesons into exclusive final states containing a J / ψ meson. The final states were selected from 19.6 pb-1 of pp̅ collisions recorded by the Collider Detector at Fermilab. These data are interpreted to determine the b quark fragmentation fractions f_u, f_d, and f_s. We also determine the branching fractions for the decay modes B⁺→J / ψK⁺, B⁺→J / ψK^*(892)⁺, B⁰→J / ψK⁰, B⁰→J / ψK^*(892)⁰, and B_s⁰→J / ψφ(1020). We discuss the implications of these measurements to B meson decay models.

The properties of high-mass multijet events produced at the Fermilab proton-antiproton collider are compared with leading order QCD matrix element predictions, QCD parton shower Monte Carlo predictions, and the predictions from a model in which events are distributed uniformly over the available multibody phase space. Multijet distributions corresponding to (4N-4) variables that span the N-body parameter space are found to be well described by the QCD calculations for inclusive three-jet, four-jet, and five-jet events. The agreement between data, QCD matrix element calculations, and QCD parton shower Monte Carlo predictions suggests that 2→2 scattering plus gluon radiation provides a good first approximation to the full LO QCD matrix element for events with three, four, or even five jets in the final state.

We present a measurement of the forward-backward charge asymmetry of the process pp̅ →Z⁰/γ+X, Z⁰/γ→e⁺e^- at M_ee>M_Z, using 110 pb^-1 of data at sqrt[s]  =  1.8  TeV collected at the Collider Detector at Fermilab. The measured charge asymmetries are 0.43±0.10 in the invariant mass region M_ee>105  GeV/c², and 0.070±0.016 in the region 75<M_ee<105  GeV/c². These results are consistent with the standard model values of 0.528±0.009 and 0.052±0.002, respectively.

The lifetime of the B_s⁰ meson is measured using the exclusive decay mode B_s⁰→J/ψ φ, where J/ψ→μ⁺μ^- and φ→K⁺K^-. The data sample consists of 110 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8  TeV, collected by the CDF detector at the Fermilab Tevatron collider during 1992–1995. We find 58±12 signal events, and the B_s⁰ meson lifetime is determined to be τ_Bs⁰  =  1.34_-0.19^+0.23(stat)±0.05(syst) ps. This result is consistent with previous measurements of the B_s⁰, B⁺, and B_d⁰ meson lifetimes and with theoretical predictions.

The lifetime of Λ_b⁰ is measured using the semileptonic decay Λ_b⁰→Λ_c⁺ℓ^-ν̅ , where the Λ_c⁺ is reconstructed through its decay Λ_c⁺→pK^-π⁺. The data were collected by the CDF detector at the Tevatron Collider during 1992–1995 and correspond to an integrated luminosity of 110 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8 TeV. From a fit to the decay length distribution of the Λ_c-lepton system from 197±25 signal events, the lifetime of Λ_b⁰ is measured to be 1.32±0.15±0.07 ps.

We present a study of events with Z bosons and hadronic jets produced in p̅ p collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 Z→e⁺e^- decays from 106 pb^-1 of integrated luminosity collected using the CDF detector at the Fermilab Tevatron Collider. The Z+≥n 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.

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≤|η|≤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(α_s³) perturbative QCD calculations. Various possible explanations for the high- E_T excess are discussed.

We present the result of a search for charged Higgs boson decays of the top quark, produced in pp̅ collisions at sqrt[s]=1.8 TeV. When the charged Higgs boson is heavy and decays to a τ lepton, which subsequently decays hadronically, the resulting events have a unique signature: large missing transverse energy and the low-charged-multiplicity τ. Data collected in 1992 and 1993 at the Collider Detector at Fermilab, corresponding to 18.7±0.7 pb^-1, exclude new regions of combined top quark and charged Higgs boson mass, in extensions to the standard model with two Higgs doublets.

We report on a search for the flavor-changing neutral current decays B_d,s⁰→μ⁺μ^-, B⁺→μ⁺μ^-K⁺, and B⁰→μ⁺μ^-K^*0 using data from pp̅ collisions at sqrt[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(B⁰→μ⁺μ^-)<1.6×10^-6, B(B_s⁰→μ⁺μ^-)<8.4×10^-6, B(B⁺→μ⁺μ^-K⁺)<1.0×10^-5, and B(B⁰→μ⁺μ^-K^*0)<2.5×10^-5.

The lifetimes of the B^- and B̅ ⁰ mesons are measured using the partially reconstructed semileptonic decays B̅ →Dℓ^-ν̅ X, where D is either a D⁰ or D^*+ meson. The data were collected by the CDF detector at the Fermilab Tevatron collider during 1992–1993 and correspond to 19.3 pb^-1 of p̅ p collisions at sqrt[s]  =  1.8 TeV. We measure the decay length distributions and find the lifetimes to be τ(B^-)  =  1.56±0.13±0.06 ps and τ(B̅ ⁰)  =  1.54±0.08±0.06 ps, and the ratio of lifetimes to be τ(B^-)/τ(B̅ ⁰)  =  1.01±0.11±0.02, where the first uncertainties are statistical and the second are systematic.

We have searched for chargino-neutralino production (χ̃₁^±χ̃₂⁰) in 1.8 TeV pp̅ collisions, followed by their leptonic decays χ̃₁^±→χ̃₁⁰ℓ^±ν and χ̃₂⁰→χ̃₁⁰ℓ⁺ℓ^-. These trilepton events are expected within a framework of the minimal supersymmetric standard model (MSSM). In a 19.1 pb^-1 data sample collected with a Collider Detector at Fermilab, no trilepton events were observed. Upper limits on σ(pp̅ →χ̃₁^±χ̃₂⁰)̇BR(χ̃₁^±χ̃₂⁰→3ℓ+X) were obtained for various MSSM parameter space regions, yielding new 95% confidence level lower limits for the neutralino (χ̃₂⁰) mass which extend as high as 49 GeV/c².

We present a measurement of σB(W→eν) and σB(Z⁰→e⁺e^-) in proton-antiproton collisions at sqrt[s]  =  1.8 TeV using a significantly improved understanding of the integrated luminosity. The data represent an integrated luminosity of 19.7 pb^-1 from the 1992–1993 run with the Collider Detector at Fermilab. We find σB(W→eν)  =  2.49±0.12 nb and σB(Z⁰→e⁺e^-)  =  0.231±0.012 nb.

We have searched for the rare decay W^±→π^±+γ in 16.7 pb ^-1 of data taken in proton-antiproton collisions at sqrt[s]  =  1.8 TeV with the CDF detector at Fermilab. We find one event consistent with the expected signal, and estimate the background to be 2.6±1.0(stat)±1.3(syst) events. Without background subtraction, we find the ratio of partial widths to be γ(W^±→π^±+γ)/γ(W^±→e^±+ν)≤2.0×10^-3 at the 95% confidence level.

We measure the mass of the B_s⁰ meson by reconstructing the decay chain B_s⁰→J/ψφ, J/ψ→μ⁺μ^-, and φ→K⁺K^-. The data are obtained from 19.3 pb^-1 of integrated luminosity of p¯p collisions at √s=1.8 TeV using the Collider Detector at Fermilab. A sample of 80 000 inclusive J/ψ→μ⁺μ^- events is used to study systematic biases in track reconstruction and to calibrate the momentum scale. We reconstruct the kinematically similar decays B⁺→J/ψK⁺ and B⁰→J/ψK^*0 to study the mass measurement technique used for the B_s⁰ meson. Based on the observation of 32 ± 6 candidates, the mass of the B_s⁰ meson is measured to be 5369.9 ± 2.3 ± 1.3 MeV/c² and the mass difference between B_s⁰ and the average mass of B⁺ and B⁰ is determined to be 89.7 ± 2.7 ± 1.2 MeV/c². © 1996 The American Physical Society.

We report on the reconstruction of the decay mode B⁰→J/ψ K_S⁰ using 19.3 pb^-1 of data collected by the Collider Detector at Fermilab in p̅ p collisions at sqrt[s]  =  1.8 TeV. A signal of 41.8±6.9 events, with a signal-to-background ratio of 9:1, is observed. Three additional decay modes B⁺→J/ψ K⁺, B⁰→J/ψ K^*(892)⁰, and B⁺→J/ψ K^*(892)⁺ are reconstructed. We measure three ratios of branching ratios, each one relative to the B⁺→J/ψ K⁺ mode. We also report the ratio of decay rates, γ(B→J/ψ K^*)/γ(B→J/ψ K), for the vector-vector relative to the vector-pseudoscalar modes, to be 1.32±0.23(stat)±0.16(syst).

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 pp̅ collisions at sqrt[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.

We report on measurements of differential μ-b¯ cross sections, where the muon is from a semileptonic b decay and the b¯ is identified using precision track reconstruction in jets. The semidifferential correlated cross sections dσ/dE_T^b¯, dσ/dp_T^b¯, and dσ/dδφ(μ-b¯) for p_T^μ≳9 GeV/c, ‖η^μ‖〈0.6,E_T^b¯〉 10 GeV, ‖η^b¯‖<1.5 are presented and compared to next-to-leading order QCD calculations. © 1996 The American Physical Society.

We report on measurements of the ϒ(1S), ϒ(2S), and ϒ(3S) differential, (d²σ / dP_tdy)_y=0, and integrated cross sections in pp̅ collisions at sqrt[s]=1.8 TeV using a sample of 16.6 ± 0.6 pb^-1 collected by the Collider Detector at Fermilab. The three resonances were reconstructed through the decay ϒ→μ⁺μ^-. Comparison is made to a leading order QCD prediction.

We analyze a sample of W+jet events collected with the Collider Detector at Fermilab (CDF) in pp̅ collisions at sqrt[s]=1.8 TeV to study tt̅ production. We employ a simple kinematical variable H, defined as the scalar sum of the transverse energies of the lepton, neutrino, and jets. For events with a W boson and four or more jets, the shape of the H distribution deviates by 3.8 standard deviations from that expected from known backgrounds to tt̅ production. However, this distribution agrees well with a linear combination of background and tt̅ events, the agreement being best for a top mass of 180 GeV/c².

This paper presents a measurement of the mass of the W boson using data collected with the CDF detector during the 1992–1993 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 3268 W→μν events recorded in an integrated luminosity of 19.7 pb^-1 gives M_W^μ=80.310±0.205 (stat)±0.130 (syst) GeV/c². A fit to the transverse mass spectrum of a sample of 5718 W→eν events recorded in 18.2 pb^-1 gives M_W^e=80.490±0.145 (stat)±0.175 (syst) GeV/c². Combining the muon and electron results, accounting for correlated uncertainties, yields M_W=80.410±0.180 GeV/c².

This Letter reports on measurements of the longitudinal polarization fractions in the decays B_d→J/ψ K^*0 and B_s→J/ψ φ using data collected with the Collider Detector at Fermilab. B_d mesons are reconstructed through the decay chain B_d→J/ψ K^*0, J/ψ→μ⁺μ^-, K^*0→K⁺π^-. A sample of 65±10 B_d events is used to obtain a longitudinal polarization fraction of γ_L/γ  =  0.65±0.10(stat)±0.04(syst). B_s mesons are reconstructed through the decay chain B_s→J/ψ φ, J/ψ→μ⁺μ^-, φ→K⁺K^-. A sample of 19±5 B_s events is used to obtain the result γ_L/γ  =  0.56±0.21(stat)_-0.04^+0.02(syst).

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.