Search Results (464 total)

A combined mass and particle identification fit is used to make the first observation of the decay B̅ _s⁰→D_s^±K^∓ and measure the branching fraction of B̅ _s⁰→D_s^±K^∓ relative to B̅ _s⁰→D_s⁺π^-. This analysis uses 1.2  fb^-1 integrated luminosity of pp̅ collisions at sqrt[s]=1.96  TeV collected with the CDF II detector at the Fermilab Tevatron collider. We observe a B̅ _s⁰→D_s^±K^∓ signal with a statistical significance of 8.1σ and measure B(B̅ _s⁰→D_s^±K^∓)/B(B̅ _s⁰→D_s⁺π^-)=0.097±0.018(stat)±0.009(syst).

We present a search for associated production of the standard model Higgs boson and a Z boson where the Z boson decays to two leptons and the Higgs decays to a pair of b quarks in pp̅ collisions at the Fermilab Tevatron. We use event probabilities based on standard model matrix elements to construct a likelihood function of the Higgs content of the data sample. In a CDF data sample corresponding to an integrated luminosity of 2.7  fb^-1 we see no evidence of a Higgs boson with a mass between 100  GeV/c² and 150  GeV/c². We set 95% confidence level upper limits on the cross section for ZH production as a function of the Higgs boson mass m_H; the limit is 8.2 times the standard model prediction at m_H=115  GeV/c².

We report the observation of the bottom, doubly-strange baryon Ω_b^- through the decay chain Ω_b^-→J/ψΩ^-, where J/ψ→μ⁺μ^-, Ω^-→ΛK^-, and Λ→pπ^-, using 4.2  fb^-1 of data from pp̅ collisions at sqrt[s]=1.96  TeV, and recorded with the Collider Detector at Fermilab. A signal is observed whose probability of arising from a background fluctuation is 4.0×10^-8, or 5.5 Gaussian standard deviations. The Ω_b^- mass is measured to be 6054.4±6.8(stat)±0.9(syst)  MeV/c². The lifetime of the Ω_b^- baryon is measured to be 1.13_-0.40^+0.53(stat)±0.02(syst)  ps. In addition, for the Ξ_b^- baryon we measure a mass of 5790.9±2.6(stat)±0.8(syst)  MeV/c² and a lifetime of 1.56_-0.25^+0.27(stat)±0.02(syst)  ps. Under the assumption that the Ξ_b^- and Ω_b^- are produced with similar kinematic distributions to the Λ_b⁰ baryon, we find σ(Ξ_b^-)B(Ξ_b^-→J/ψΞ^-) / σ(Λ_b⁰)B(Λ_b⁰→J/ψΛ)=0.167_-0.025^+0.037(stat)±0.012(syst) and σ(Ω_b^-)B(Ω_b^-→J/ψΩ^-) / σ(Λ_b⁰)B(Λ_b⁰→J/ψΛ)=0.045_-0.012^+0.017(stat)±  0.004(syst) for baryons produced with transverse momentum in the range of 6–20  GeV/c.

We present an analysis of the mass of the X(3872) reconstructed via its decay to J/ψπ⁺π^- using 2.4  fb^-1 of integrated luminosity from pp̅ collisions at sqrt[s]=1.96  TeV, collected with the CDF II detector at the Fermilab Tevatron. The possible existence of two nearby mass states is investigated. Within the limits of our experimental resolution the data are consistent with a single state, and having no evidence for two states we set upper limits on the mass difference between two hypothetical states for different assumed ratios of contributions to the observed peak. For equal contributions, the 95% confidence level upper limit on the mass difference is 3.6  MeV/c². Under the single-state model the X(3872) mass is measured to be 3871.61±0.16(stat)±0.19(syst)  MeV/c², which is the most precise determination to date.

We report on a search for the process pp̅ →γ+W/Z with W/Z→qq̅ in events containing two jets and a photon at the center-of-mass energy sqrt[s]=1.96  TeV, using 184  pb^-1 of data collected by the CDF II detector. A neural network event selection has been developed to optimize the rejection of the large QCD production background; it is shown that this method gives a significant improvement in both signal-to-noise ratio and signal sensitivity, as compared with an event selection based on conventional cuts. An upper limit is presented for the γ+W/Z production cross section with the W and Z decaying hadronically.

We present a signature-based search for the anomalous production of events containing a photon, two jets, of which at least one is identified as originating from a b quark, and missing transverse energy (E̸_T). The search uses data corresponding to 2.0  fb^-1 of integrated luminosity from pp̅ collisions at a center-of-mass energy of sqrt[s]=1.96  TeV, collected with the CDF II detector at the Fermilab Tevatron. From 6.697 47×10⁶ events with a photon candidate with transverse energy E_T>25  GeV, we find 617 events with E̸_T>25  GeV and two or more jets with E_T>15  GeV, at least one identified as originating from a b quark, versus an expectation of 607±113 events. Increasing the requirement on E̸_T to 50 GeV, we find 28 events versus an expectation of 30±11 events. We find no indications of non-standard-model phenomena.

We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay t→Zc using a technique employing ratios of W and Z production, measured in pp̅ data corresponding to an integrated luminosity of 1.52  fb^-1. The analysis uses a comparison of two decay chains, pp̅ →tt̅ →WbWb→ℓνbjjb and pp̅ →tt̅ →ZcWb→ℓℓcjjb, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton identification over the multiyear data set using another ratio of W and Z production, in this case the observed ratio of inclusive production of W to Z bosons. To improve the discrimination against standard model backgrounds to top-quark decays, we calculate the top-quark mass for each event with two leptons and four jets assuming it is a tt̅ event with one of the top quarks decaying to Zc. For additional background discrimination we require at least one jet to be identified as originating from a b quark. No significant signal is found and we set an upper limit on the FCNC branching ratio Br(t→Zc) using a likelihood constructed from the ℓℓcjjb top-quark mass distribution and the number of ℓνbjjb events. Limits are set as a function of the helicity of the Z boson produced in the FCNC decay. For 100% longitudinally-polarized Z bosons we find limits of 8.3% and 9.3% (95% C.L.) depending on the assumptions regarding the theoretical top-quark pair production cross section.

We present the first measurement of the mass of the top quark in a sample of tt̅ →ℓν̅ bb̅ qq̅ events (where ℓ=e,μ) selected by identifying jets containing a muon candidate from the semileptonic decay of heavy-flavor hadrons (soft muon b tagging). The pp̅ collision data used correspond to an integrated luminosity of 2  fb^-1 and were collected by the CDF II detector at the Fermilab Tevatron Collider. The measurement is based on a novel technique exploiting the invariant mass of a subset of the decay particles, specifically the lepton from the W boson of the t→Wb decay and the muon from a semileptonic b decay. We fit template histograms, derived from simulation of tt̅ events and a modeling of the background, to the mass distribution observed in the data and measure a top quark mass of 180.5±12.0(stat)±3.6(syst)  GeV/c², consistent with the current world average value.

We report on the first direct search for charged Higgs bosons decaying into cs̅ in tt̅ events produced by pp̅ collisions at sqrt[s]=1.96  TeV. The search uses a data sample corresponding to an integrated luminosity of 2.2  fb^-1 collected by the CDF II detector at Fermilab and looks for a resonance in the invariant mass distribution of two jets in the lepton+jets sample of tt̅ candidates. We observe no evidence of charged Higgs bosons in top quark decays. Hence, 95% upper limits on the top quark decay branching ratio are placed at B(t→H⁺b)< 0.1 to 0.3 for charged Higgs boson masses of 60 to 150  GeV/c² assuming B(H⁺→cs̅ )=1.0. The upper limits on B(t→H⁺b) are also used as model-independent limits on the decay branching ratio of top quarks to generic scalar charged bosons beyond the standard model.

We present a search for a standard model Higgs boson produced in association with a W boson using 2.7  fb^-1 of integrated luminosity of pp̅ collision data taken at sqrt[s]=1.96  TeV. Limits on the Higgs boson production rate are obtained for masses between 100 and 150  GeV/c². Through the use of multivariate techniques, the analysis achieves an observed (expected) 95% confidence level upper limit of 5.6 (4.8) times the theoretically expected production cross section for a standard model Higgs boson with a mass of 115  GeV/c².

We present the first observation in hadronic collisions of the electroweak production of vector boson pairs (VV, V=W, Z) where one boson decays to a dijet final state. The data correspond to 3.5  fb^-1 of integrated luminosity of pp̅ collisions at sqrt[s]=1.96  TeV collected by the CDF II detector at the Fermilab Tevatron. We observe 1516±239(stat)±144(syst) diboson candidate events and measure a cross section σ(pp̅ →VV+X) of 18.0±2.8(stat)±2.4(syst)±1.1(lumi)  pb, in agreement with the expectations of the standard model.

We report the observation of single top-quark production using 3.2  fb^-1 of pp̅ collision data with sqrt[s]=1.96  TeV collected by the Collider Detector at Fermilab. The significance of the observed data is 5.0 standard deviations, and the expected sensitivity for standard model production and decay is in excess of 5.9 standard deviations. Assuming m_t=175  GeV/c², we measure a cross section of 2.3_-0.5^+0.6(stat+syst)  pb, extract the CKM matrix-element value |V_tb|=0.91±0.11(stat+syst)±0.07(theory), and set the limit |V_tb|>0.71 at the 95% C.L.

We have measured the differential cross section for the inclusive production of ψ(2S) mesons decaying to μ⁺μ^- that were produced in prompt or B-decay processes from pp̅ collisions at 1.96 TeV. These measurements have been made using a data set from an integrated luminosity of 1.1  fb^-1 collected by the CDF II detector at Fermilab. For events with transverse momentum p_T(ψ(2S))>2  GeV/c and rapidity |y(ψ(2S))|<0.6 we measure the integrated inclusive cross section σ(pp̅ →ψ(2S)X)·Br(ψ(2S)→μ⁺μ^-) to be 3.29±0.04(stat)±0.32(syst)  nb.

A search for a narrow diphoton mass resonance is presented based on data from 3.0  fb^-1 of integrated luminosity from pp̅ collisions at sqrt[s]=1.96  TeV collected by the CDF experiment. No evidence of a resonance in the diphoton mass spectrum is observed, and upper limits are set on the cross section times branching fraction of the resonant state as a function of Higgs boson mass. The resulting limits exclude Higgs bosons with masses below 106  GeV/c² at a 95% Bayesian credibility level for one fermiophobic benchmark model.

We compare the inclusive production of events containing a lepton (ℓ), a photon (γ), significant transverse momentum imbalance (E̸_T), and a jet identified as containing a b-quark, to SM predictions. The search uses data produced in proton-antiproton collisions at sqrt[s]=1.96  TeV corresponding to 1.9  fb^-1 of integrated luminosity taken with the CDF detector. We find 28 ℓγbE̸_T events versus an expectation of 31.0_-3.5^+4.1 events. If we further require events to contain at least three jets and large total transverse energy, the largest SM source is radiative top-quark pair production, tt̅ +γ. In the data we observe 16 tt̅ γ candidate events versus an expectation from SM sources of 11.2_-2.1^+2.3. Assuming the difference between the observed number and the predicted non-top-quark total of 6.8_-2.0^+2.2 is due to SM top-quark production, we estimate the tt̅ γ cross section to be 0.15±0.08  pb.

We present new limits on resonant tb̅ production in pp̅ collisions at sqrt[s]=1.96  TeV, using 1.9  fb^-1 of data recorded with the CDF II detector at the Fermilab Tevatron. We reconstruct a candidate tb̅ mass in events with a lepton, neutrino candidate, and two or three jets, and search for anomalous tb̅ production as modeled by W^′→tb̅ . We set a new limit on a right-handed W^′ with standard model-like coupling, excluding any mass below 800  GeV/c² at 95% C.L. The cross section for any narrow, resonant tb̅ production between 750 and 950  GeV/c² is found to be less than 0.28 pb at 95% C.L. We also present an exclusion of the W^′ coupling strength versus W^′ mass over the range 300–950  GeV/c².

We search for new charmless decays of neutral b hadrons to pairs of charged hadrons, using 1  fb^-1 of data collected by the CDF  II detector at the Fermilab Tevatron. We report the first observation of the B_s⁰→K^-π⁺ decay and measure B(B_s⁰→K^-π⁺)=(5.0±0.7(stat)±0.8(syst))×10^-6. We also report the first observation of charmless b-baryon decays, and measure B(Λ_b⁰→pπ^-)=(3.5±0.6(stat)±0.9(syst))×10^-6 and B(Λ_b⁰→pK^-)=(5.6±0.8(stat)±1.5(syst))×10^-6. No evidence is found for other modes, and we set the limit B(B_s⁰→π⁺π^-)<1.2×10^-6 at 90% C.L.

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 that correspond to an integrated luminosity of approximately 1.9  fb^-1. We select events consistent with a signature of a single charged lepton (e^±/μ^±), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method, a jet probability tagging method, and a neural network filter. We use kinematic information in an artificial neural network to improve discrimination between signal and background compared to previous analyses. The observed number of events and the neural network output distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching fraction ranging from 1.2 to 1.1 pb or 7.5 to 102 times the standard model expectation for Higgs boson masses from 110 to 150  GeV/c², respectively.

We performed a signature-based search for long-lived charged massive particles produced in 1.0  fb^-1 of pp̅ collisions at sqrt[s]=1.96  TeV, collected with the CDF II detector using a high transverse-momentum (p_T) muon trigger. The search used time of flight to isolate slowly moving, high-p_T particles. One event passed our selection cuts with an expected background of 1.9±0.2 events. We set an upper bound on the production cross section and, interpreting this result within the context of a stable scalar top-quark model, set a lower limit on the particle mass of 249  GeV/c² at 95% C.L.

We present a search for WW and WZ production in final states that contain a charged lepton (electron or muon) and at least two jets, produced in sqrt[s]=1.96  TeV pp̅ collisions at the Fermilab Tevatron, using data corresponding to 1.2  fb^-1 of integrated luminosity collected with the CDF II detector. Diboson production in this decay channel has yet to be observed at hadron colliders due to the large single W plus jets background. An artificial neural network has been developed to increase signal sensitivity, as compared with an event selection based on conventional cuts. We set a 95% confidence level upper limit of σ_WW×BR(W→ℓν_ℓ,W→jets)+σ_WZ×BR(W→ℓν_ℓ,Z→jets)<2.88  pb, which is consistent with the standard model next-to-leading-order cross section calculation for this decay channel of 2.09±0.12  pb.

Evidence is reported for a narrow structure near the J/ψϕ threshold in exclusive B⁺→J/ψϕK⁺ decays produced in p̅ p collisions at sqrt[s]=1.96  TeV. A signal of 14±5 events, with statistical significance in excess of 3.8 standard deviations, is observed in a data sample corresponding to an integrated luminosity of 2.7  fb^-1, collected by the CDF II detector. The mass and natural width of the structure are measured to be 4143.0±2.9(stat)±1.2(syst)  MeV/c² and 11.7_-5.0^+8.3(stat)±3.7(syst)  MeV/c².

In CDF we have observed the reactions p+p̅ →p+X+p̅ , with X being a centrally produced J/ψ, ψ(2S), or χ_c0, and γγ→μ⁺μ^- in pp̅ collisions at sqrt[s]=1.96  TeV. The event signature requires two oppositely charged central muons, and either no other particles or one additional photon detected. Exclusive vector meson production is as expected for elastic photoproduction, γ+p→J/ψ(ψ(2S))+p, observed here for the first time in hadron-hadron collisions. We also observe exclusive χ_c0→J/ψ+γ. The cross sections dσ / dy|_y=0 for J/ψ, ψ(2S), and χ_c0 are 3.92±0.25(stat)±0.52(syst)  nb, 0.53±0.09(stat)±0.10(syst)  nb, and 76±10(stat)±10(syst)  nb, respectively, and the continuum is consistent with QED. We put an upper limit on the cross section for Odderon exchange in exclusive J/ψ production.

This paper reports a measurement of the cross section for the pair production of top quarks in pp̅ collisions at sqrt[s]=1.96  TeV at the Fermilab Tevatron. The data were collected from the CDF run II detector in a set of runs with a total integrated luminosity of 1.1  fb^-1. The cross section is measured in the dilepton channel, the subset of tt̅ events in which both top quarks decay through t→Wb→ℓνb, where ℓ=e, μ, or τ. The lepton pair is reconstructed as one identified electron or muon and one isolated track. The use of an isolated track to identify the second lepton increases the tt̅ acceptance, particularly for the case in which one W decays as W→τν. The purity of the sample may be further improved at the cost of a reduction in the number of signal events, by requiring an identified b jet. We present the results of measurements performed with and without the request of an identified b jet. The former is the first published CDF result for which a b-jet requirement is added to the dilepton selection. In the CDF data there are 129 pretag lepton+track candidate events, of which 69 are tagged. With the tagging information, the sample is divided into tagged and untagged subsamples, and a combined cross section is calculated by maximizing a likelihood. The result is σ_tt̅ =9.6±1.2(stat)_-0.5^+0.6(sys)±0.6(lum)  pb, assuming a branching ratio of BR(W→ℓν)=10.8% and a top mass of m_t=175  GeV/c².