43 research outputs found

    Top Quark Mass Measurement from Dilepton Events at CDF II with the Matrix-Element Method

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    We describe a measurement of the top quark mass using events with two charged leptons collected by the CDF II detector from ppˉp\bar{p} collisions with s=1.96\sqrt s = 1.96 TeV at the Fermilab Tevatron. The likelihood in top mass is calculated for each event by convoluting the leading order matrix element describing qqˉttˉbνbˉνq\bar{q} \to t\bar{t} \to b\ell\nu_{\ell}\bar{b}\ell'\nu_{\ell'} with detector resolution functions. The presence of background events in the data sample is modeled using similar calculations involving the matrix elements for major background processes. In a data sample with integrated luminosity of 340 pb1^{-1}, we observe 33 candidate events and measure Mtop=165.2±6.1(stat.)±3.4(syst.) GeV/c2.M_{top} = 165.2 \pm 6.1(\textrm{stat.}) \pm 3.4(\textrm{syst.}) \mathrm{~GeV}/c^2. This measurement represents the first application of this method to events with two charged leptons and is the most precise single measurement of the top quark mass in this channel.Comment: 21 pages, 14 figure

    Search for New Physics in Lepton + Photon + X Events with L=305 pb-1 of ppbar Collisions at roots=1.96 TeV

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    We present results of a search for anomalous production of events containing a charged lepton (either electron or muon) and a photon, both with high transverse momentum, accompanied by additional signatures, X, including missing transverse energy (MET) and additional leptons and photons. We use the same kinematic selection criteria as in a previous CDF search, but with a substantially larger data set, 305 pb-1, a ppbar collision energy of 1.96 TeV, and the upgraded CDF II detector. We find 42 Lepton+Photon+MET events versus a standard model expectation of 37.3 +- 5.4 events. The level of excess observed in Run I, 16 events with an expectation of 7.6 +- 0.7 events (corresponding to a 2.7 sigma effect), is not supported by the new data. In the signature of Multi-Lepton+Photon+X we observe 31 events versus an expectation of 23.0 +- 2.7 events. In this sample we find no events with an extra photon or MET and so find no events like the one ee+gg+MET event observed in Run I.Comment: 7 pages, 3 figures, 1 table. Accepted to PR

    Measurement of the Ratio of Branching Fractions B(D0 -> K+ pi-)/B(D0 -> K- pi+) using the CDF II Detector

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    We present a measurement of R_B, the ratio of the branching fraction for the rare decay D0 -> K+ pi- to that for the Cabibbo-favored decay D0 -> K- pi+. Charge conjugate decays are implicitly included. A signal of 2005 +/- 104 events for the decay D0 -> K+ pi- is obtained using the CDF II detector at the Fermilab Tevatron collider. The data set corresponds to an integrated luminosity of 0.35 1/fb produced in p-bar/p collisions at sqrt{s}=1.96 TeV. Assuming no mixing, we find R_B = [ 4.05 +/- 0.21 (stat) +/- 0.11 (syst) ] x 10(-3). This measurement is consistent with the world average, and comparable in accuracy with the best measurements from other experiments.Comment: 7 pages, 3 figure

    Search for Excited and Exotic Muons in the mu+gamma Decay Channel in p-pbar Collisions at sqrt{s} = 1.96 TeV

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    We present a search for excited and exotic muon states mu*, conducted using an integrated luminosity of 371 pb^{-1} of data collected in p-pbar collisions at sqrt{s} = 1.96 TeV at the Tevatron with the CDF II detector. We search for associated production of mu+mu* followed by the decay mu* -> mu+gamma, resulting in the mu+mu+gamma final state. We compare the data to model predictions as a function of the mass of the excited muon M(mu*), the compositeness energy scale Lambda, and the gauge coupling factor f. No signal above the standard model expectation is observed in the mu+gamma mass spectrum. In the contact interaction model, we exclude 107 < M(mu*) < 853 GeV/c^2 for Lambda = M(mu*); in the gauge-mediated model, we exclude 100 < M(mu) < 410 GeV/c^2 for f/Lambda = 0.01/GeV. These 95% confidence level exclusions extend previous limits and are the first hadron collider results on mu* production in the gauge-mediated model.Comment: Submitted to Phys. Rev. Lett., 7 pages, 4 Figure

    Measurement of the Top Quark Mass using Template Methods on Dilepton Events in Proton-Antiproton Collisions at sqrt(s)=1.96 TeV

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    We describe a measurement of the top quark mass from events produced in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV, using the Collider Detector at Fermilab. We identify top-antitop candidates where both W bosons from the top quarks decay into leptons (electron, muon, or tau plus neutrino) from a data sample of 360 inverse picobarns. The top quark mass is reconstructed in each event separately by three different methods, which draw upon simulated distributions of the neutrino pseudorapidity, top-antitop longitudinal momentum, or neutrino azimuthal angle in order to extract probability distributions for the top quark mass. For each method, representative mass distributions, or templates, are constructed from simulated samples of signal and background events, and parameterized to form continuous probability density functions. A likelihood fit incorporating these parameterized templates is then performed on the data sample masses in order to derive a final top quark mass. Combining the three template methods, taking into account correlations in their statistical and systematic uncertainties, results in a top quark mass measurement of 170.1 +/- 6.0 (stat) +/- 4.1 (syst) GeV/c^2.Comment: 52 pages, 23 figures, 5 tables. Submitted to Physical Review

    Search for excited and exotic muons in the mu gamma decay channel in p(p)over-bar collisions root s=1.96 TeV

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    We search for excited and exotic muon states mu(*) using an integrated luminosity of 371 pb(-1) of p (p) over bar collision data at root s=1.96 TeV. We search for associated production of mu mu(*) followed by the decay mu(*)-\u3emu gamma. We compare the data to model predictions as a function of the mass of the excited muon M-mu(*), the compositeness energy scale Lambda, and the gauge coupling factor f. No signal above the standard model expectation is observed. We exclude 107 \u3c M-mu(*)\u3c 853 GeV/c(2) for Lambda=M-mu(*) in the contact interaction model, and 100 \u3c M-mu(*)\u3c 410 GeV/c(2) for f/Lambda=10(-2) GeV-1 in the gauge-mediated model, both at the 95% confidence level

    Observation of Bs to Psi(2S)phi and Measurement of Ratio of Branching Fractions B (Bs --> Psi(2S)phi) / B (Bs --> J/Psi phi)

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    We report the first observation of Bs to Psi(2S) phi signals using 360 pb^-1 of CDF Run II data sample, where Psi(2S) decays into mu+mu- and J/psi pi+pi- modes with phi decays to K+K-. We have measured the relative branching ratio of Br(Bs to Psi(2S)phi)/Br(Bs to J/psi phi) using J/psi, Psi(2S) to mu+mu- decay mode. We obtain Br(Bs to Psi(2S)phi)/Br(Bs to J/psi phi) = 0.52 +- 0.13 (stat.) +- 0.04 (syst.) +- 0.06 (BR).Comment: 14 pages, 4 figures, submitted to Phys.Rev.Let

    Observation of B-s(0)-\u3e K+K- and measurements of branching fractions of charmless two-body decays of B-0 and B-s(0) mesons in pp collisions at root s=1.96 TeV

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    We search for decays of the type B-(s)(0)-\u3e h(+)h(\u27-) (where h,h(\u27)=K or pi) in 180 pb(-1) of (p) over barp collisions collected at the Tevatron by the upgraded Collider Detector at Fermilab. We report the first observation of the new mode B-s(0)-\u3e K+K- with a yield of 236 +/- 32 events, corresponding to (f(s)/f(d))xB(B-s(0)-\u3e K+K-)/B(B-0 -\u3e K+pi(-))=0.46 +/- 0.08(stat)+/- 0.07(syst), where f(s)/f(d) is the ratio of production fractions of B-s(0) and B-0. We find results in agreement with world averages for the B-0 modes, and set the following new limits at 90% C.L.: B(B-s(0)-\u3e K-pi(+))\u3c 5.6x10(-6) and B(B-s(0)-\u3epi(+)pi(-))\u3c 1.7x10(-6)
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