Search Results (338 total)

We present measurements of the forward-backward charge asymmetry in top pair production using 1.9  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV recorded with the Collider Detector at Fermilab II. Correcting for acceptance and measurement dilutions we obtain parton-level asymmetries of A_FB^pp̅ =0.17±0.08 in the pp̅ frame and A_FB^tt̅ =0.24±0.14 in the tt̅ frame. The values are consistent with the standard model expectation and disfavor exotic production mechanisms with significant negative values.

We report a search for the flavor-changing neutral-current decay of the top quark t→Zq (q=u, c) in pp̅ collisions at sqrt[s]=1.96  TeV using a data sample corresponding to an integrated luminosity of 1.9  fb^-1 collected by the CDF II detector. This decay is strongly suppressed in the standard model and an observation of a signal at the Fermilab Tevatron would be an indication of physics beyond the standard model. Using Z+≥4 jet final state candidate events, with and without an identified bottom quark jet, we obtain an upper limit of B(t→Zq)<3.7% at 95% C.L.

We present the results of searches for large extra dimensions in samples of events with large missing transverse energy E̸_T and either a photon or a jet produced in pp̅ collisions at sqrt[s]=1.96  TeV collected with the Collider Detector at Fermilab II. For γ+E̸_T and jet+E̸_T candidate samples corresponding to 2.0 and 1.1  fb^-1 of integrated luminosity, respectively, we observe good agreement with standard model expectations and obtain a combined lower limit on the fundamental parameter of the large extra dimensions model M_D as a function of the number of extra dimensions in the model.

We present a measurement of the shapes of b-jets using 300  pb^-1 of data obtained with the upgraded Collider Detector at Fermilab (CDF II) in pp̅ collisions at center-of-mass energy sqrt[s]=1.96  TeV. This measurement covers a wide transverse momentum range, from 52 to 300  GeV/c. Samples of heavy-flavor enhanced jets together with inclusive jets are used to extract the average shapes of b-jets. The b-jets are expected to be broader than inclusive jets. Moreover, b-jets containing a single b-quark are expected to be narrower than those containing a bb̅ pair from gluon splitting. The measured b-jet shapes are found to be significantly broader than expected from the pythia and herwig Monte Carlo simulations. This effect may arise from an underestimation of the fraction of b-jets originating from gluon splitting in these simulations. The jet shape distributions provided in this paper could be compared to any full Monte Carlo simulation and could be used to further constrain the various parameters.

We present a measurement of the inclusive jet cross section in pp̅ collisions at sqrt[s]=1.96  TeV based on data collected by the CDF II detector with an integrated luminosity of 1.13  fb^-1. The measurement was made using the cone-based midpoint jet clustering algorithm in the rapidity region of |y|<2.1. The results are consistent with next-to-leading-order perturbative QCD predictions based on recent parton distribution functions (PDFs), and are expected to provide increased precision in PDFs at high parton momentum fraction x. The results are also compared to the recent inclusive jet cross section measurement using the k_T jet clustering algorithm, and we find that the ratio of the cross sections measured with the two algorithms is in agreement with theoretical expectations over a large range of jet transverse momentum and rapidity.

We search for pair production of doubly charged Higgs particles (H^±±) followed by decays into electron-tau (eτ) and muon-tau (μτ) pairs using data (350  pb^-1) collected from p̅ p collisions at sqrt[s]=1.96  TeV by the CDF II experiment. We search separately for cases where three or four final-state leptons are detected, and combine results for exclusive decays to left-handed eτ (μτ) pairs. We set an H^±± lower mass limit of 114(112)  GeV/c² at the 95% confidence level.

We present the results of the first hadron collider search for heavy, long-lived neutralinos that decay via χ˜₁⁰→γG˜ in gauge-mediated supersymmetry breaking models. Using an integrated luminosity of 570±34  pb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV, we select γ+jet+missing transverse energy candidate events based on the arrival time of a high-energy photon at the electromagnetic calorimeter as measured with a timing system that was recently installed on the CDF II detector. We find 2 events, consistent with the background estimate of 1.3±0.7 events. While our search strategy does not rely on model-specific dynamics, we set cross section limits and place the world-best 95% C.L. lower limit on the χ˜₁⁰ mass of 101  GeV/c² at τ_χ˜1⁰=5  ns.

We present a search for standard model Higgs boson production in association with a W boson in proton-antiproton collisions (pp̅ →W^±H→ℓνbb̅ ) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 1  fb^-1. We select events consistent with a signature of a single lepton (e^±/μ^±), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a neural network filter technique. The observed number of events and the dijet mass distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio ranging from 3.9 to 1.3 pb for Higgs boson masses from 110 to 150  GeV/c², respectively.

We search for pair production of supersymmetric top quarks (t˜₁), followed by R-parity violating decay t˜₁→τb with a branching ratio β, using 322  pb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV collected by the upgraded Collider Detector at Fermilab. Two candidate events pass our final selection criteria, consistent with the standard model expectation. We set upper limits on the cross section σ(t˜₁t˜̅ ₁)×β² as a function of the top-squark mass m(t˜₁). Assuming β=1, we set a 95% confidence level limit m(t˜₁)>153  GeV/c². The limits are also applicable to the case of a third-generation scalar leptoquark (LQ₃) decaying LQ₃→τb.

We report the results of a search for the anomalous production of a massive particle decaying to four electrons via two Z⁰ bosons in 1.1  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV collected by the CDF II detector at Fermilab. We employ optimized electron identification criteria to maximize acceptance and efficiency. We estimate the backgrounds in the invariant mass range 500–1000  GeV/c² to be 0.028±0.009(stat)±0.011(syst) events. We observe zero events in this search region. Assuming a Randall-Sundrum graviton production model, we set 95% C.L. limits on σ×BF(G→Z⁰Z⁰)<4–6  pb, depending on the graviton mass.

We present a new method for studying high-p_T dilepton events (e^±e^∓, μ^±μ^∓, e^±μ^∓) and simultaneously extracting the production cross sections of pp̅ →tt̅ , pp̅ →W⁺W^-, and pp̅ →Z⁰→τ⁺τ^- at a center-of-mass energy of sqrt[s]=1.96  TeV. We perform a likelihood fit to the dilepton data in a parameter space defined by the missing transverse energy and the number of jets in the event. Our results, which use 360  pb^-1 of data recorded with the CDF II detector at the Fermilab Tevatron Collider, are σ(tt̅ )=8.5_-2.2^+2.7  pb, σ(W⁺W^-)=16.3_-4.4^+5.2  pb, and σ(Z⁰→τ⁺τ^-)=291_-46⁺⁵⁰  pb.

Data collected in run II of the Fermilab Tevatron are searched for indications of new electroweak scale physics. Rather than focusing on particular new physics scenarios, CDF data are analyzed for discrepancies with respect to the standard model prediction. A model-independent approach (Vista) considers the gross features of the data and is sensitive to new large cross section physics. A quasi-model-independent approach (Sleuth) searches for a significant excess of events with large summed transverse momentum and is particularly sensitive to new electroweak scale physics that appears predominantly in one final state. This global search for new physics in over 300 exclusive final states in 927  pb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV reveals no such significant indication of physics beyond the standard model.

We report on a search for narrow-width particles decaying to a top and antitop quark pair. The data set used in the analysis corresponds to an integrated luminosity of 680  pb^-1 collected with the Collider Detector at Fermilab in run II. We present 95% confidence level upper limits on the cross section times branching ratio. Assuming a specific top-color-assisted technicolor production model, the leptophobic Z^′ with width Γ_Z^′=0.012M_Z^′, we exclude the mass range M_Z^′<725  GeV/c² at the 95% confidence level.

We describe a measurement of the W boson mass m_W using 200  pb^-1 of sqrt[s]=1.96  TeV pp̅ collision data taken with the CDF II detector. With a sample of 63 964 W→eν candidates and 51 128 W→μν candidates, we measure m_W=[80.413±0.034(stat)±0.034(sys)=80.413±0.048]  GeV/c². This is the single most precise m_W measurement to date. When combined with other measured electroweak parameters, this result further constrains the properties of new unobserved particles coupling to W and Z bosons.

We search for a third generation vector leptoquark (VLQ3) that decays to a b quark and tau lepton using the CDF II detector and 320  pb^-1 of integrated luminosity from the Fermilab Tevatron. Observing a number of events in agreement with standard model expectations, we obtain, assuming Yang-Mills (minimal) couplings, the most stringent upper limit on the VLQ3 pair production cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317  GeV/c² (251  GeV/c²) at 95% C.L.

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use ∼1  fb^-1 integrated luminosity of pp̅ collisions at sqrt[s]=1.96  TeV recorded by the Collider Detector at Fermilab II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248±43 (14.4±2.7) are expected from standard model background processes. We observe no significant excess over the expected background and thus set 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 to 140  GeV/c². For a mass of 115  GeV/c², the observed (expected) limit is 20.4 (14.2) times the standard model prediction.

We report the first evidence of Z boson pair production at a hadron collider with a significance exceeding 4 standard deviations. This result is based on a data sample corresponding to 1.9  fb^-1 of integrated luminosity from pp̅ collisions at sqrt[s]=1.96  TeV collected with the Collider Detector at Fermilab II detector. In the ℓℓℓ^′ℓ^′ channel, we observe three ZZ candidates with an expected background of 0.096_-0.063^+0.092 events. In the ℓℓνν channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of ℓℓℓ^′ℓ^′ and ℓℓνν channels, we observe an excess of events with a probability of 5.1×10^-6 to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is σ(pp̅ →ZZ)=1.4_-0.6^+0.7(stat+syst)  pb, consistent with the standard model expectation.

We present the first measurement of two-particle momentum correlations in jets produced in pp̅ collisions at sqrt[s]=1.96  TeV. Results are obtained for charged particles within a restricted cone with an opening angle of 0.5 radians around the jet axis and for events with dijet masses between 66 and 563  GeV/c². A comparison of the experimental data to theoretical predictions obtained for partons within the framework of resummed perturbative QCD in the next-to-leading log approximation shows that the parton momentum correlations survive the hadronization stage of jet fragmentation, giving further support to the hypothesis of local parton-hadron duality. The extracted value of the next-to-leading-log-approximation parton shower cutoff scale Q_eff set equal to Λ_QCD is found to be (1.4_-0.7^+0.9)×100  MeV.

The B_c^± meson is observed through the decay B_c^±→J/ψπ^±, in data corresponding to an integrated luminosity of 2.4  fb^-1 recorded by the Collider Detector at Fermilab II detector at the Fermilab Tevatron. A signal of 108±15 candidates is observed, with a significance that exceeds 8σ. The mass of the B_c^± meson is measured to be 6275.6±2.9(stat)±2.5(syst)  MeV/c².

We present a measurement of the correlated bb̅ production cross section. The data used in this analysis were taken with the upgraded CDF detector (CDF II) at the Fermilab Tevatron collider, and correspond to an integrated luminosity of 742  pb^-1. We utilize muon pairs with invariant mass 5≤m_μμ≤80  GeV/c² produced by bb̅ double semileptonic decays. For muons with p_T≥3  GeV/c and |η|≤0.7, that are produced by b and b̅ quarks with p_T≥2  GeV/c and |y|≤1.3, we measure σ_{b→μ,b̅ →μ}=1549±133  pb. We compare this result with theoretical predictions and previous measurements. We also report the measurement of σ_{c→μ,c̅ →μ}, a by-product of the study of the background to bb̅ production.

We present the results of a search for pair production of a new heavy toplike quark t^′ decaying to a W boson and another quark using the Collider Detector at Fermilab II detector in run II of the Tevatron pp̅ collider. Using a data sample corresponding to 760  pb^-1 of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t^′ quark mass to a combination of standard model processes and t^′ pair production. We see no evidence for t^′t̅ ^′ production, and we infer a lower limit of 256  GeV/c² on the mass of the t^′ at 95% C.L. assuming standard strong couplings for the t^′.

This Letter describes the first determination of bounds on the CP-violation parameter 2β_s using B_s⁰ decays in which the flavor of the bottom meson at production is identified. The result is based on approximately 2000 B_s⁰→J/ψϕ decays reconstructed in a 1.35  fb^-1 data sample collected with the CDF II detector using pp̅ collisions produced at the Fermilab Tevatron. We report confidence regions in the two-dimensional space of 2β_s and the decay-width difference ΔΓ. Assuming the standard model predictions of 2β_s and ΔΓ, the probability of a deviation as large as the level of the observed data is 15%, corresponding to 1.5 Gaussian standard deviations.

This paper describes the first measurement of b-quark fragmentation fractions into bottom hadrons in Run II of the Tevatron Collider at Fermilab. The result is based on a 360  pb^-1 sample of data collected with the CDF II detector in pp̅ collisions at sqrt[s]=1.96  TeV. Semileptonic decays of B̅ ⁰, B^-, and B̅ _s⁰ mesons, as well as Λ_b⁰ baryons, are reconstructed. For an effective bottom hadron p_T threshold of 7  GeV/c, the fragmentation fractions are measured to be f_u/f_d=1.054±0.018(stat)_-0.045^+0.025(sys)±0.058(B), f_s/(f_u+f_d)=0.160±0.005(stat)_-0.010^+0.011(sys)_-0.034^+0.057(B), and f_Λb/(f_u+f_d)=0.281±0.012(stat)_-0.056^+0.058(sys)_-0.087^+0.128(B), where the uncertainty B is due to uncertainties on measured branching ratios. The value of f_s/(f_u+f_d) agrees within one standard deviation with previous CDF measurements and the world average of this quantity, which is dominated by LEP measurements. However, the ratio f_Λb/(f_u+f_d) is approximately twice the value previously measured at LEP. The approximately 2σ discrepancy is examined in terms of kinematic differences between the two production environments.

We measure the mean lifetime τ=2/(Γ_L+Γ_H) and the decay-width difference ΔΓ=Γ_L-Γ_H of the light and heavy mass eigenstates of the B_s⁰ meson, B_sL⁰ and B_sH⁰, in B_s⁰→J/ψϕ decays using 1.7  fb^-1 of data collected with the CDF II detector at the Fermilab Tevatron pp̅ collider. Assuming CP conservation, a good approximation for the B_s⁰ system in the standard model, we obtain ΔΓ=0.076_-0.063^+0.059(stat)±0.006(syst)  ps^-1 and τ=1.52±0.04(stat)±0.02(syst)  ps, the most precise measurements to date. Our constraints on the weak phase and ΔΓ are consistent with CP conservation.