Search Results (142 total)

We measure the masses of b hadrons in exclusively reconstructed final states containing a J/ψ→μ^-μ⁺ decay using 220  pb^-1 of data collected by the CDF II experiment. We find: m(B⁺)=5279.10±0.41_(stat.)±0.36_(sys.)  MeV/c², m(B⁰)=5279.63±0.53_(stat.)±0.33_(sys.)  MeV/c², m(B_s⁰)=5366.01±0.73_(stat.)±0.33_(sys.)  MeV/c², m(Λ_b⁰)=5619.7±1.2_(stat.)±1.2_(sys.)  MeV/c². m(B⁺)-m(B⁰)=-0.53±0.67_(stat.)±0.14_(sys.)  MeV/c², m(B_s⁰)-m(B⁰)=86.38±0.90_(stat.)±0.06_(sys.)  MeV/c², m(Λ_b⁰)-m(B⁰)=339.2±1.4_(stat.)±0.1_(sys.)  MeV/c². The measurements of the B_s⁰, Λ_b⁰ mass, m(B_s⁰)-m(B⁰) and m(Λ_b⁰)-m(B⁰) mass difference are of better precision than the current world averages.

We present the first measurement of the A₂ and A₃ angular coefficients of the W boson produced in proton-antiproton collisions. We study W→eν_e and W→μν_μ candidate events produced in association with at least one jet at CDF, during Run Ia and Run Ib of the Tevatron at sqrt[s]=1.8  TeV. The corresponding integrated luminosity was 110  pb^-1. The jet balances the transverse momentum of the W and introduces QCD effects in W boson production. The extraction of the angular coefficients is achieved through the direct measurement of the azimuthal angle of the charged lepton in the Collins-Soper rest-frame of the W boson. The angular coefficients are measured as a function of the transverse momentum of the W boson. The electron, muon, and combined results are in good agreement with the standard model prediction, up to order α_s² in QCD.

We report the first evidence for a fully reconstructed decay mode of the B_c^± meson in the channel B_c^±→J/ψπ^±, with J/ψ→μ⁺μ^-. The analysis is based on an integrated luminosity of 360  pb^-1 in pp̅ collisions at 1.96 TeV center of mass energy collected by the Collider Detector at Fermilab. We observe 14.6±4.6 signal events with a background of 7.1±0.9 events, and a fit to the J/ψπ^± mass spectrum yields a B_c^± mass of 6285.7±5.3(stat)±1.2(syst)  MeV/c². The probability of a peak of this magnitude occurring by random fluctuation in the search region is estimated as 0.012%.

We present a study of the dijet invariant mass distribution for the reaction p̅ p→two   jets+γ+X, at a center of mass energy of 1.8 TeV, using data collected by the CDF experiment. We compare the data to predictions for the production of a photon with two jets, together with the resonant processes p̅ p→W/Z+γ+X, in which the W and Z bosons decay hadronically. A fit is made to the dijet invariant mass distribution combining the nonresonant background and resonant processes. We use the result to establish a limit for the inclusive production cross section of W/Z+γ with hadronic decay of the W and Z bosons.

A search for the direct production of Higgs bosons in the di-tau decay mode is performed with 86.3±3.5  pb^-1 of data collected with the Collider Detector at Fermilab during the 1994–1995 data taking period of the Tevatron. We search for events where one tau decays to an electron plus neutrinos and the other tau decays hadronically. We perform a counting experiment and set limits on the cross section for supersymmetric Higgs boson production where tan⁡β is large and m_A is small. For a benchmark parameter space point where m_A⁰=100  GeV/c² and tan⁡β=50, we limit the production cross section multiplied by the branching ratio to be less than 77.9 pb at the 95% confidence level compared to the theoretically predicted value of 11.0 pb. This is the first search for Higgs bosons decaying to tau pairs at a hadron collider.

We report on a search for pair production of first-generation scalar leptoquarks (LQ) in pp̅ collisions at sqrt[s]=1.96   TeV using an integrated luminosity of 203   pb^-1 collected at the Fermilab Tevatron collider by the CDF experiment. We observe no evidence for LQ production in the topologies arising from LQLQ̅ →eqeq and LQLQ̅ →eqνq, and derive 95% C.L. upper limits on the LQ production cross section. The results are combined with those obtained from a separately reported CDF search in the topology arising from LQLQ̅ →νqνq and 95% C.L. lower limits on the LQ mass as a function of β=BR(LQ→eq) are derived. The limits are 236, 205 and 145  GeV/c² for β=1, β=0.5 and β=0.1, respectively.

We present the results of a search for anomalous resonant production of tau lepton pairs with large invariant mass, the first such search using the CDF II Detector in Run II of the Tevatron pp̅ collider. Such anomalous production could arise from various new physics processes. In a data sample corresponding to 195  pb^-1 of integrated luminosity we predict 2.8±0.5 events from standard model background processes and observe 4. We use this result to set limits on the production of heavy scalar and vector particles decaying to tau lepton pairs.

We report on a search for Λ_b⁰→pπ^- and Λ_b⁰→pK^- (and charge conjugate) decays in pp̅ collisions at sqrt[s]=1.96  TeV using 193  pb^-1 of data collected by the CDF II experiment at the Fermilab Tevatron Collider. Data were collected using a track trigger that has been optimized to select tracks belonging to a secondary vertex that is typical of two-body charmless decays of b-flavored hadrons, including Λ_b⁰ baryons. As no Λ_b⁰ signal was observed, we set the upper limits on the branching fraction B(Λ_b⁰→ph^-), where h is K or π, of 2.3×10^-5 at 90% C.L. and 2.9×10^-5 at 95% C.L.

We present a measurement of the top pair production cross section in pp̅ collisions at sqrt[s]=1.96  TeV. We collect a data sample with an integrated luminosity of 194±11  pb^-1 with the CDF II detector at the Fermilab Tevatron. We use an artificial neural network technique to discriminate between top pair production and background processes in a sample of 519 lepton+jets events, which have one isolated energetic charged lepton, large missing transverse energy and at least three energetic jets. We measure the top pair production cross section to be σ_tt̅ =6.6±1.1±1.5  pb, where the first uncertainty is statistical and the second is systematic.

We present a study of the production of K_S⁰ and Λ⁰ in inelastic pp̅ collisions at sqrt[s]=1800 and 630 GeV using data collected by the CDF experiment at the Fermilab Tevatron. Analyses of K_S⁰ and Λ⁰ multiplicity and transverse momentum distributions, as well as of the dependencies of the average number and ⟨p_T⟩ of K_S⁰ and Λ⁰ on charged particle multiplicity, are reported. Systematic comparisons are performed for the full sample of inelastic collisions, and for the low and high momentum transfer subsamples, at the two energies. The p_T distributions extend above 8  GeV/c, showing a ⟨p_T⟩ higher than previous measurements. The dependence of the mean K_S⁰(Λ⁰) p_T on the charged particle multiplicity for the three samples shows a behavior analogous to that of charged primary tracks.

We present a measurement of the ratio of top-quark branching fractions R=B(t→Wb)/B(t→Wq), where q can be a b, s, or a d quark, using lepton-plus-jets and dilepton data sets with an integrated luminosity of ∼162  pb^-1 collected with the Collider Detector at Fermilab during Run II of the Tevatron. The measurement is derived from the relative numbers of tt̅ events with different multiplicity of identified secondary vertices. We set a lower limit of R>0.61 at 95% confidence level.

We present a search for long-lived doubly charged Higgs bosons (H^±±), with signatures of high ionization energy loss and muonlike penetration. We use 292  pb^-1 of data collected in pp̅ collisions at sqrt[s]=1.96  TeV by the CDF II detector at the Fermilab Tevatron. Observing no evidence of long-lived doubly charged particle production, we exclude H_L^±± and H_R^±± bosons with masses below 133  GeV/c² and 109  GeV/c², respectively. In the degenerate case we exclude H^±± mass below 146  GeV/c². All limits are quoted at the 95% confidence level.

We present a measurement of the tt̅ production cross section using 194   pb^-1 of CDF II data using events with a high transverse momentum electron or muon, three or more jets, and missing transverse energy. The measurement assumes 100% t→Wb branching fraction. Events consistent with tt̅ decay are found by identifying jets containing heavy-flavor semileptonic decays to muons. The dominant backgrounds are evaluated directly from the data. Based on 20 candidate events and an expected background of 9.5±1.1 events, we measure a production cross section of 5.3±3.3_-1.0^+1.3   pb, in agreement with the standard model.

We present a new search for H⁰V production, where H⁰ is a scalar Higgs boson decaying into bb̅ with branching ratio β, and V is a Z⁰ boson decaying into e⁺e^-, μ⁺μ^-, or νν̅ . This search is then combined with previous searches for H⁰V where V is a W^± boson or a hadronically decaying Z⁰. The data sample consists of 106±4  pb^-1 of pp̅ collisions at sqrt[s]=1.8  TeV accumulated by the Collider Detector at Fermilab. Observing no evidence of a signal, we set 95% Bayesian credibility level upper limits on σ(pp̅ →H⁰V)×β. For H⁰ masses of 90, 110, and 130  GeV/c², the limits are 7.8, 7.2, and 6.6 pb, respectively.

We present the first evidence of charmless decays of the B_s⁰ meson, the decay B_s⁰→ϕϕ, and a measurement of the branching ratio BR(B_s⁰→ϕϕ) using 180  pb^-1 of data collected by the CDF II experiment at the Fermilab Tevatron collider. In addition, the BR and direct CP asymmetry for the B⁺→ϕK⁺ decay are measured. We obtain BR(B_s⁰→ϕϕ)=[14_-5⁺⁶(stat)±6(syst)]×10^-6, BR(B⁺→ϕK⁺)=[7.6±1.3(stat)±0.6(syst)]×10^-6, and A_CP(B⁺→ϕK⁺)=-0.07±0.17(stat)+0.03 / -0.02(syst). Both decays are governed in the standard model by second order (penguin) b→ss̅ s amplitudes.

We report a measurement of the rate of prompt diphoton production in pp̅ collisions at sqrt[s]=1.96  TeV using a data sample of 207  pb^-1 collected with the upgraded Collider Detector at Fermilab. The background from nonprompt sources is determined using a statistical method based on differences in the electromagnetic showers. The cross section is measured as a function of the diphoton mass, the transverse momentum of the diphoton system, and the azimuthal angle between the two photons and is found to be consistent with perturbative QCD predictions.

We report on a search for anomalous kinematics of tt̅ dilepton events in pp̅ collisions at sqrt[s]=1.96  TeV using 193  pb^-1 of data collected with the CDF II detector. We developed a new a priori technique designed to isolate the subset in a data sample revealing the largest deviation from standard model (SM) expectations and to quantify the significance of this departure. In the four-variable space considered, no particular subset shows a significant discrepancy, and we find that the probability of obtaining a data sample less consistent with the SM than what is observed is 1.0%–4.5%.

We report on a study of jet shapes in inclusive jet production in pp̅ collisions at sqrt[s]=1.96   TeV using the upgraded collider detector at Fermilab in Run II (CDF II) and based on an integrated luminosity of 170   pb^-1. Measurements are carried out on jets with rapidity 0.1<|Y^jet|<0.7 and transverse momentum 37  GeV/c<P_T^jet<380  GeV/c. The jets have been corrected to the hadron level. The measured jet shapes are compared to leading-order QCD parton-shower Monte Carlo predictions as implemented in the PYTHIA and HERWIG programs. PYTHIA, tuned to describe the underlying event as measured in CDF Run I, provides a better description of the measured jet shapes than does PYTHIA or HERWIG with their default parameters.

We present a measurement of the W⁺W^- production cross section using 184  pb^-1 of pp̅ collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W⁺W^-→ℓ⁺νℓ^-ν̅ , where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0_-0.8^+2.2 events. The resulting W⁺W^- production cross-section measurement of σ(pp̅ →W⁺W^-)=14.6_-5.1^+5.8(stat)_-3.0^+1.8(syst)±0.9(lum)  pb agrees well with the standard model expectation.

We report on a search for the pair production of scalar leptoquarks (LQ), using 191  pb^-1 of proton-antiproton collision data recorded by the CDF experiment during Run II of the Tevatron. The leptoquarks are sought via their decay into a neutrino and quark yielding missing transverse energy and several jets of large transverse energy. No evidence for LQ production is observed, and limits are set on σ(pp̅ →LQLQ̅ X→νν̅ qq̅ X). Using a next-to-leading order theoretical prediction of the cross section for LQ production, we exclude first-generation LQ in the mass interval 78 to 117  GeV/c² at the 95% confidence level for BR(LQ→νq)=100%.

We present a search for ZZ and ZW vector boson pair production in pp̅ collisions at sqrt[s]=1.96  TeV using the leptonic decay channels ZZ→llνν, ZZ→lll^′l^′, and ZW→lll^′ν. In a data sample corresponding to an integrated luminosity of 194  pb^-1 collected with the Collider Detector at Fermilab, 3 candidate events are found with an expected background of 1.0±0.2 events. We set a 95% confidence level upper limit of 15.2 pb on the cross section for ZZ plus ZW production, compared to the standard model prediction of 5.0±0.4  pb.

We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, N_q and N_g, produced at the Fermilab Tevatron in pp̅ collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of θ_c=0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q=E_jetθ_c varies in the range from 12 to 25 GeV. At Q=19.2  GeV, the ratio of multiplicities r=N_g/N_q is found to be 1.64±0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations.

We have measured the azimuthal angular correlation of bb̅ production, using 86.5  pb^-1 of data collected by Collider Detector at Fermilab (CDF) in pp̅ collisions at sqrt[s]=1.8  TeV during 1994–1995. In high-energy pp̅ collisions, such as at the Tevatron, bb̅ production can be schematically categorized into three mechanisms. The leading-order (LO) process is “flavor creation,” where both b and b̅ quarks substantially participate in the hard scattering and result in a distinct back-to-back signal in final state. The “flavor excitation” and the “gluon splitting” processes, which appear at next-leading-order (NLO), are known to make a comparable contribution to total bb̅ cross section, while providing very different opening angle distributions from the LO process. An azimuthal opening angle between bottom and antibottom, Δϕ, has been used for the correlation measurement to probe the interaction creating bb̅ pairs. The Δϕ distribution has been obtained from two different methods. One method measures the Δϕ between bottom hadrons using events with two reconstructed secondary vertex tags. The other method uses bb̅ →(J/ψX)(ℓX^′) events, where the charged lepton (ℓ) is an electron (e) or a muon (μ), to measure Δϕ between bottom quarks. The bb̅ purity is determined as a function of Δϕ by fitting the decay length of the J/ψ and the impact parameter of the ℓ. Both methods quantify the contribution from higher-order production mechanisms by the fraction of the bb̅ pairs produced in the same azimuthal hemisphere, f_toward. The measured f_toward values are consistent with both parton shower Monte Carlo and NLO QCD predictions.

We report a measurement of the tt̅ production cross section using the CDF II detector at the Fermilab Tevatron. The data consist of events with an energetic electron or muon, missing transverse energy, and three or more hadronic jets, at least one of which is identified as a b-quark jet by reconstructing a secondary vertex. The background fraction is determined from a fit of the transverse energy of the leading jet. Using 162±10  pb^-1 of data, the total cross section is found to be 6.0±1.6(stat.)±1.2(syst.)  pb, which is consistent with the standard model prediction.