44 research outputs found
Combination of CDF and D0 results on the W boson mass and width
No full textThe results based on 1992–95 data (Run 1) from the CDF and D0 experiments on the measurements of the W boson mass and width are presented, along with the combined results. We report a Tevatron collider average MW=80.456±0.059  GeV. We also report the Tevatron collider average of the directly measured W boson width ΓW=2.115±0.105  GeV. We describe a new joint analysis of the direct W mass and width measurements. Assuming the validity of the standard model, we combine the directly measured W boson width with the width extracted from the ratio of W and Z boson leptonic partial cross sections. This combined result for the Tevatron is ΓW=2.135±0.050  GeV. Finally, we use the measurements of the direct total W width and the leptonic branching ratio to extract the leptonic partial width Γ(W→eν)=224±13  MeV
Diffractive W and Z production at the Fermilab Tevatron
No full textWe report on a measurement of the fraction of events with a W or Z boson which are produced diffractively in p̅ p collisions at √s=1.96 [square root of s = 1.96] TeV, using data from 0.6 fb-1 [fb superscript -1] of integrated luminosity collected with the CDF II detector equipped with a Roman-pot spectrometer that detects the p̅ from p̅ +p→p̅ +[X+W/Z]. We find that (1.00±0.11)% of Ws and (0.88±0.22)% of Zs are produced diffractively in a region of antiproton or proton fractional momentum loss ξ [xi] of 0.03<ξ<0.10 [0.03 < xi <0.10] and 4-momentum transferred squared t of -1<t<0 (GeV/c)2 [(GeV/c) superscript 2], where we account for the events in which the proton scatters diffractively while the antiproton dissociates, p̅ +p→[X+W/Z]+p, by doubling the measured proton dissociation fraction. We also report on searches for W and Z production in double Pomeron exchange, p+p̅ →p+[X+W/Z]+p̅ , and on exclusive Z production, p̅ +p→p̅ +Z+p. No signal is seen above background for these processes, and comparisons are made with expectations.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio
Measurement of the W+W- Production Cross Section and Search for Anomalous WW gamma and WWZ Couplings in p(p)over-bar Collisions at root s 1.96 TeV
No full textThis Letter describes the current most precise measurement of the W boson pair production cross section and most sensitive test of anomalous WW gamma and WWZ couplings in p (p) over bar collisions at a center-of-mass energy of 1.96 TeV. The WW candidates are reconstructed from decays containing two charged leptons and two neutrinos. Using data collected by the CDF II detector from 3: 6 fb(-1) of integrated luminosity, a total of 654 candidate events are observed with an expected background of 320 +/- 47 events. The measured cross section is sigma(p (p) over bar -> W+W- +X) = 12.1 +/- 0.9(stat)(-1.4)(+1.6)(syst) pb, which is in good agreement with the standard model prediction. The same data sample is used to place constraints on anomalous WW gamma and WWZ couplings
First Measurement of the b-Jet Cross Section in Events with a W Boson in p(p)over-bar Collisions at root s=1.96 TeV
No full textThe cross section for jets from b quarks produced with a W boson has been measured in p (p) over bar collision data from 1: 9 fb(-1) of integrated luminosity recorded by the CDF II detector at the Tevatron. The W + b-jets process poses a significant background in measurements of top quark production and prominent searches for the Higgs boson. We measure a b-jet cross section of 2.74 + 0.27(stat) +/- 0.42(syst) pb in association with a single flavor of leptonic W boson decay over a limited kinematic phase space. This measured result cannot be accommodated in several available theoretical predictions
Measurement of W-Boson Polarization in Top-Quark Decay in p(p)over-bar Collisions at root s=1.96 TeV
No full textWe report measurements of the polarization of W bosons from top-quark decays using 2.7 fb(-1) of p (p) over bar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c(2), three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f(0)) and right-handed (f(0)) W bosons yields the model- independent results f(0) =0. 88 +/- 0.11(stat) +/- 0.06(syst) and f(+) = 0.15 +/- 0.07(stat) +/- 0.06(syst) with a correlation coefficient of -0.59. A measurement of f(0) [f(+)] constraining f(+) [f(0)] to its standard model value of 0.0 [0.7] yields f(0) 0.70 + 0.07(stat) +/- 0.04(syst) [f(+) - 0.01 +/- 0.02(stat) +/- 0.05(syst)]. All these results are consistent with standard model expectations. We achieve the single most precise measurements of f(0) for both the model- independent and modeldependent determinations
Search for Technicolor Particles Produced in Association with a W Boson at CDF
No full textWe present a search for the technicolor particles ρT and πT in the process pp̅ →ρT→WπT at a center of mass energy of √s=1.96 TeV. The search uses a data sample corresponding to approximately 1.9 fb-1 of integrated luminosity accumulated by the CDF II detector at the Fermilab Tevatron. The event signature we consider is W→ℓν and πT→bb̅ , bc̅ or bu̅ depending on the πT charge. We select events with a single high-pT electron or muon, large missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with multiple b-tagging algorithms. The observed number of events and the invariant mass distributions are consistent with the standard model background expectations, and we exclude a region at 95% confidence level in the ρT-πT mass plane. As a result, a large fraction of the region m(ρT)=180–250 GeV/c2 and m(πT)=95–145 GeV/c2 is excluded
Search for WW and WZ Resonances Decaying to Electron, Missing E-T, and Two Jets in p(p)over-bar Collisions at root s=1.96 TeV.
No full textUsing data from 2: 9 fb(-1) of integrated luminosity collected with the CDF II detector at the Tevatron, we search for resonances decaying into a pair of on-shell gauge bosons, WW or WZ, where one W decays into an electron and a neutrino, and the other boson decays into two jets. We observed no statistically significant excess above the expected standard model background, and we set cross section limits at 95% confidence level on G* (Randall-Sundrum graviton), Z', and W' bosons. By comparing these limits to theoretical cross sections, mass exclusion regions for the three particles are derived. The mass exclusion regions for Z' and W' are further evaluated as a function of their gauge coupling strength
Observation of single top quark production and measurement of |V subscript tb| with CDF
No full textWe report the observation of electroweak single top quark production in 3.2 fb-1 [fb superscript -1] of pp̅ collision data collected by the Collider Detector at Fermilab at √s=1.96 TeV [square root of s=1.96 TeV]. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3-0.5+0.6(stat+sys) [2.3 subscript -0.5 superscript +0.6 (stat + sys)] pb, extract the value of the Cabibbo-Kobayashi-Maskawa matrix element |Vtb|=0.91-0.11+0.11(stat+sys)±0.07 [|V subscript tb|=0.91 subscript -0.11 superscript +0.11 (stat + sys)±0.07] (theory), and set a lower limit |Vtb|>0.71 [|V subscript tb|>0.71] at the 95% C.L., assuming mt=175 [m subscript t =175] GeV/c2 [GeV / c superscript 2].United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio
Search for the Higgs Boson Using Neural Networks in Events with Missing Energy and b-Quark Jets in p(p)over-bar Collisions at root s=1.96 TeV
No full textWe report on a search for the standard model Higgs boson produced in association with a W or Z boson in p (p) over bar collisions at root s = 1.96 TeV recorded by the CDF II experiment at the Tevatron in a data sample corresponding to an integrated luminosity of 2.1 fb(-1). We consider events which have no identified charged leptons, an imbalance in transverse momentum, and two or three jets where at least one jet is consistent with originating from the decay of a b hadron. We find good agreement between data and background predictions. We place 95% confidence level upper limits on the production cross section for several Higgs boson masses ranging from 110 GeV/c(2) to 150 GeV/c(2). For a mass of 115 GeV/c(2) the observed (expected) limit is 6.9 (5.6) times the standard model prediction
Direct Top-Quark Width Measurement at CDF
No full textWe present a measurement of the top-quark width in the lepton + jets decay channel of t (t) over bar events produced in p (p) over bar collisions at Fermilab's Tevatron collider and collected by the CDF II detector. From a data sample corresponding to 4.3 fb(-1) of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of the hadronically decaying W boson that comes from the top-quark decay are reconstructed for each event and compared with templates of different top-quark widths (Gamma(t)) and deviations from nominal jet energy scale (Delta(JES)) to perform a simultaneous fit for both parameters, where Delta(JES) is used for the in situ calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95% confidence level (CL) of Gamma(t) < 7.6 GeV and a two-sided 68% CL interval of 0.3 GeV < Gamma(t) < 4.4 GeV for a top-quark mass of 172.5 GeV/c(2), which are consistent with the standard model prediction
