Search Results (218 total)

The 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 M_W=80.456±0.059  GeV. We also report the Tevatron collider average of the directly measured W boson width Γ_W=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 Γ_W=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.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

We measure the relative rate of production of orbitally excited (L=1) states of B mesons (B^**) by observing their decays into Bπ^±. We reconstruct B mesons through semileptonic decay channels using data collected in pp̅ collisions at sqrt[s]=1.8 TeV. The fraction of light B mesons that are produced as L=1B^** states is measured to be 0.28±0.06(stat)±0.03(syst). We also measure the collective mass of the B^** states, and quantify the result by quoting the (model-dependent) mass of the lowest B^** state to be m(B₁)=5.71±0.02 GeV/c².

We present a measurement of the W boson mass using data collected with the CDF detector during the 1994–1995 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 30115 W→eν events recorded in an integrated luminosity of 84 pb^-1 gives a mass M_W=80.473±0.065(stat)±0.092(syst) GeV/c². A fit to the transverse mass spectrum of a sample of 14740 W→μν events from 80 pb^-1 gives a mass M_W=80.465±0.100(stat)±0.103(syst) GeV/c². The dominant contributions to the sys- tematic uncertainties are the uncertainties in the electron energy scale and the muon momentum scale, 0.075 GeV/c² and 0.085 GeV/c², respectively. The combined value for the electron and muon channel is M_W=80.470±0.089 GeV/c². When combined with previously published CDF measurements, we obtain M_W=80.433±0.079 GeV/c².

This report describes a measurement of the top quark mass in pp̅ collisions at a center of mass energy of 1.8 TeV. The data sample was collected with the CDF detector during the 1992–1995 collider run at the Fermilab Tevatron, and corresponds to an integrated luminosity of 106 pb^-1. Candidate tt̅ events in the “lepton+jets” decay channel provide our most precise measurement of the top quark mass. For each event a top quark mass is determined by using energy and momentum constraints on the production of the tt̅ pair and its subsequent decay. A likelihood fit to the distribution of reconstructed masses in the data sample gives a top quark mass in the lepton+jets channel of 176.1±5.1(stat)±5.3(syst) GeV/c². Combining this result with measurements from the “all-hadronic” and “dilepton” decay topologies yields a top quark mass of 176.1±6.6 GeV/c².

We report on the first measurement of the rapidity distribution dσ/dy over nearly the entire kinematic region of rapidity for e⁺e^- pairs in both the Z-boson region of 66<M_ee<116 GeV/c² and in the high mass region of M_ee>116 GeV/c². The data sample consists of 108 pb^-1 of pp̅ collisions at sqrt[s]=1.8 TeV taken by the Collider Detector at Fermilab during 1992–1995. The total cross section in the Z-boson region is measured to be 252±11 pb. The measured total cross section and dσ/dy are compared with quantum chromodynamics calculations in leading and higher orders.

An angular analysis of B⁰→J/ψK^*0 and B_s⁰→J/ψφ has been used to determine the decay amplitudes with parity-even longitudinal ( A₀) and transverse ( A_∥) polarization and parity-odd transverse ( A_⊥) polarization. The measurements are based on 190 B⁰ and 40 B_s⁰ candidates obtained from 89 pb^-1 of p̅ p collisions at the Fermilab Tevatron. The longitudinal decay amplitude dominates with |A₀|²  =  0.59±0.06±0.01 for B⁰ and |A₀|²  =  0.61±0.14±0.02 for B_s⁰ decays. The parity-odd amplitude is found to be small with |A_⊥|²  =  0.13_-0.09^+0.12±0.06 for B⁰ and |A_⊥|²  =  0.23±0.19±0.04 for B_s⁰ decays.

We report the first observation of dijet events with a double Pomeron exchange topology produced in p̅ p collisions at sqrt[s]  =  1800  GeV. The events are characterized by a leading antiproton, two jets in the central pseudorapidity region, and a large rapidity gap on the outgoing proton side. We present results on jet kinematics and production rates, compare them with corresponding results from single diffractive and inclusive dijet production, and test factorization.

This Letter describes a direct measurement of the W boson total decay width, Γ_W, using the Collider Detector at Fermilab. The measurement uses an integrated luminosity of 90 pb^-1, collected during the 1994–1995 run of the Fermilab Tevatron pp̅ collider. The width is determined by normalizing predicted signal and background distributions to 49 844 W→eν candidates and 21 806 W→μν candidates in the transverse-mass region M_T<200 GeV and then fitting the predicted shape to the 438 electron events and 196 muon events in the high- M_T region, 100<M_T<200 GeV. The result is Γ_W  =  2.04±0.11(stat)±0.09(syst) GeV.

We have measured the polarization of J/ψ and ψ(2S) mesons produced in pp̅ collisions at sqrt[s]  =  1.8 TeV, using data collected at the Collider Detector at Fermilab during 1992–1995. The polarization of promptly produced J/ψ [ψ(2S)] mesons is isolated from those produced in B-hadron decay, and measured over the kinematic range 4 [5.5]<P_T<20 GeV/c and | y|<0.6. For P_T≳12 GeV/c we do not observe significant polarization in the prompt component.

We use 106 pb ^-1 of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an antitop quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to tt̅ are presented. At the 95% confidence level, we exclude the existence of a leptophobic Z^′ boson in a model of top-color-assisted technicolor with mass M_Z^′<480  GeV/c² for natural width Γ  =  0.012M_Z^′, and M_Z^′<780  GeV/c² for Γ  =  0.04M_Z^′.

We report the results of a search for second and third generation leptoquarks using 88 pb^-1 of data recorded by the Collider Detector at Fermilab. Color triplet technipions, which play the role of scalar leptoquarks, are investigated due to their potential production in decays of strongly coupled color octet technirhos. Events with a signature of two heavy flavor jets and missing energy may indicate the decay of a second (third) generation leptoquark to a charm (bottom) quark and a neutrino. As the data are found to be consistent with standard model expectations, mass limits are determined.

Events collected by the Collider Detector at Fermilab (CDF) with an energetic jet plus large missing transverse energy can be used to search for physics beyond the standard model. We see no deviations from the expected backgrounds and set upper limits on the production of new processes. We consider in addition the production of light gravitinos and set a limit at 95% confidence level on the breaking scale sqrt[F]≥217 GeV, which excludes gravitino masses smaller than 1.1×10^-5 eV/c².

We report the results of a search for a W^′ boson produced in pp̅ collisions at a center-of-mass energy of 1.8 TeV using a 107 pb^-1 data sample recorded by the Collider Detector at Fermilab. We consider the decay channel W^′→μν_μ and search for anomalous production of high transverse mass μν_μ lepton pairs. We observe no excess of events above background and set limits on the rate of W^′ boson production and decay relative to standard model W boson production and decay using a fit of the transverse mass distribution observed. If we assume standard model strength couplings of the W^′ boson to quark and lepton pairs, we exclude a W^′ boson with invariant mass less than 660 GeV/c² at 95% confidence level.

We have searched for direct pair production of scalar top and scalar bottom quarks in 88 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8 TeV with the CDF detector. We looked for events with a pair of heavy flavor jets and missing energy, consistent with scalar top (bottom) quark decays to a charm (bottom) quark and a neutralino. The numbers of events that pass our selections show no significant deviation from standard model expectations. We compare our results to the next-to-leading order scalar quark production cross sections to exclude regions in scalar quark-neutralino mass parameter space.

Top quark production offers the unique opportunity to search for a charged Higgs boson (H^±), as the contribution from t→H⁺b→τ⁺νb can be large in extensions of the standard model. We use results from a search for top quark pair production by the Collider Detector at Fermilab (CDF) in the eτ+E_T+jets and μτ+E_T+jets signatures to set an upper limit on the branching ratio of B(t→H⁺b) in 106 pb^-1 of data. The upper limit is in the range 0.5 to 0.6 at 95% C.L. for H⁺ masses in the range 60 to 160 GeV, assuming the branching ratio for H⁺→τν is 100%. The τ lepton is detected through its 1-prong and 3-prong hadronic decays.

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c² and scalar neutrino masses of at least 40 GeV/c², we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.

We report results from a study of events with a leading antiproton of beam momentum fraction 0.905<x_F<0.965 and 4-momentum transfer squared |t|<3 GeV² produced in p̅ p collisions at sqrt[s]  =  1800 GeV at the Fermilab Tevatron collider. Approximately 2% of the events contain two jets of transverse energy E_T^jet>7 GeV. Using the dijet events, we evaluate the diffractive structure function of the antiproton and compare it with expectations based on results obtained in diffractive deep inelastic scattering experiments at the DESY ep collider HERA.

We present a measurement of the cross section for production of two or more jets as a function of dijet mass, based on an integrated luminosity of 86 pb^-1 collected with the Collider Detector at Fermilab. Our dijet mass spectrum is described within errors by next-to-leading order QCD predictions using CTEQ4HJ parton distributions, and is in good agreement with a similar measurement from the DØ experiment.

This paper reports an updated measurement of the standard model CP violation parameter sin 2β using the CDF Detector at Fermilab. The entire run I data sample of 110 pb^-1 of proton-antiproton collisions at sqrt[s]=1.8 TeV is used to identify a signal sample of ∼400 B→J/ψ K_S⁰ events, where J/ψ→μ⁺μ^- and K_S⁰→π⁺π^-. The flavor of the neutral B meson is identified at the time of production by combining information from three tagging algorithms: a same-side tag, a jet-charge tag, and a soft-lepton tag. A maximum likelihood fitting method is used to determine sin 2β=0.79_-0.44^+0.41(stat+syst). This value of sin 2β is consistent with the standard model prediction, based upon existing measurements, of a large positive CP-violating asymmetry in this decay mode.

We have reconstructed the radiative decays χ_b(1P)→ϒ(1S)γ and χ_b(2P)→ϒ(1S)γ in pp̅ collisions at sqrt[s]  =  1.8 TeV, and measured the fraction of ϒ(1S) mesons that originate from these decays. For ϒ(1S) mesons with p_T^ϒ>8.0 GeV/c, the fractions that come from χ_b(1P) and χ_b(2P) decays are [27.1±6.9(stat)±4.4(syst)]% and [10.5±4.4(stat)±1.4(syst)]%, respectively. We have derived the fraction of directly produced ϒ(1S) mesons to be [50.9±8.2(stat)±9.0(syst)]%.

We have studied the production of B hadrons in 1.8-TeV pp̅ collisions. We present measurements of the fragmentation fractions, f_u, f_d, f_s, and f_baryon, of produced b quarks that yield B⁺, B⁰, B_s⁰, and Λ̅ _b⁰ hadrons. Reconstruction of five electron-charm final states yields f_s/( f_u+f_d)  =  0.213±0.068 and f_baryon/( f_u+f_d)  =  0.118±0.042, assuming f_u  =  f_d. If all B hadrons produced in pp̅ collisions cascade to one of these four hadrons, we determine f_u  =  f_d  =  0.375±0.023, f_s  =  0.160±0.044, and f_baryon  =  0.090±0.029. If we do not assume f_u  =  f_d, we find f_d/f_u  =  0.84±0.16.

We search for color singlet technirho and technipion production in pp̅ collisions at sqrt[s]  =  1.8  TeV recorded with the Collider Detector at Fermilab. These exotic technimesons are present in a model of walking technicolor. The signatures studied are lepton plus two jets plus E_T and multijet final states. No excess of events is seen in either final state. We set an upper limit on the technirho production cross section and exclude a region in the technipion mass versus technirho mass plane.

The transverse momentum and total cross section of e⁺e^- pairs in the Z-boson region of 66<M_ee<116  GeV/c² from pp̅ collisions at sqrt[s]  =  1.8  TeV are measured using 110 pb^-1 of collisions taken by the Collider Detector at Fermilab during 1992–1995. The total cross section is measured to be 248±11 pb. The differential transverse momentum cross section is compared with calculations that match quantum chromodynamics perturbation theory at high transverse momentum with the gluon resummation formalism at low transverse momentum.

We present the results of a search for pair production of a fourth-generation charge -1 / 3 quark (b^′) in sqrt[s]  =  1.8 TeV pp̅ collisions using 88 pb^-1 of data obtained with the Collider Detector at Fermilab. We assume that both quarks decay via the flavor-changing neutral current process b^′→bZ⁰ and that the b^′ mass is greater than m_Z+m_b. We studied the decay mode b^′b^′̅ →Z⁰Z⁰bb̅ where one Z⁰ decays into e⁺e^- or μ⁺μ^- and the other decays hadronically, giving a signature of two leptons plus jets. An upper limit on the σ_{pp̅ →b^′b^′̅} ×[B(b^′→bZ⁰)]² is established as a function of the b^′ mass. We exclude at 95% confidence level a b^′ quark with mass between 100 and 199 GeV/c² for B(b^′→bZ⁰)  =  100%.