Search Results (68 total)

The design of a low-energy (4 GeV) neutrino factory (NF) is described, along with its expected performance. The neutrino factory uses a high-energy proton beam to produce charged pions. The π^± decay to produce muons (μ^±), which are collected, accelerated, and stored in a ring with long straight sections. Muons decaying in the straight sections produce neutrino beams. The scheme is based on previous designs for higher energy neutrino factories, but has an improved bunching and phase rotation system, and new acceleration, storage ring, and detector schemes tailored to the needs of the lower energy facility. Our simulations suggest that the NF scheme we describe can produce neutrino beams generated by ∼1.4×10²¹ μ⁺ per year decaying in a long straight section of the storage ring, and a similar number of μ^- decays.

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 present measurements of dark currents and x rays in a six cell 805 MHz cavity, taken as part of an rf development program for muon cooling, which requires high power, high stored energy, low frequency cavities operating in a strong magnetic field. We have done the first systematic study of the behavior of high power rf in a strong (2.5–4 T) magnetic field. Our measurements extend over a very large dynamic range in current and provide good fits to the Fowler-Nordheim field emission model assuming mechanical structures produce field enhancements at the surface. The locally enhanced field intensities we derive at the tips of these emitters are very large, (∼10  GV/m), and should produce tensile stresses comparable to the tensile strength of the copper cavity walls and should be capable of causing breakdown events. We also compare our data with estimates of tensile stresses from a variety of accelerating structures. Preliminary studies of the internal surface of the cavity and window are presented, which show splashes of copper with many sharp cone shaped protrusions and wires which can explain the experimentally measured field enhancements. We discuss a “cold copper” breakdown mechanism and briefly review alternatives. We also discuss a number of effects due to the 2.5 T solenoidal fields on the cavity such as altered field emission due to mechanical deformation of emitters, and dark current ring beams, which are produced from the irises by E×B drifts during the nonrelativistic part of the acceleration process.

We present the results of a search in pp̅ collisions at sqrt[s]=1.8 TeV for anomalous production of events containing a photon with large transverse energy and a lepton (e or μ) with large transverse energy, using 86 pb^-1 of data collected with the Collider Detector at Fermilab during the 1994–1995 collider run at the Fermilab Tevatron. The presence of large missing transverse energy (E_T), additional photons, or additional leptons in these events is also analyzed. The results are consistent with standard model expectations, with the possible exception of photon-lepton events with large E_T, for which the observed total is 16 events and the expected mean total is 7.6±0.7 events.

We present a search for the flavor-changing neutral current decay B_s→μ⁺μ^-φ in pp̅ collisions at sqrt[s]=1.8 TeV, using 91 pb^-1 of data collected at the Collider Detector at Fermilab (CDF). We find two candidate events for this decay, which are consistent with the background estimate of one event, and set an upper limit on the branching fraction of B(B_s→μ⁺μ^-φ)<6.7×10^-5 at a 95% confidence level. This is the first limit on the branching fraction of this decay.

The growth and development of “charged particle jets” produced in proton-antiproton collisions at 1.8 TeV  are studied over a transverse momentum range from 0.5 GeV/c to 50 GeV/c. A variety of leading (highest transverse momentum) charged jet observables are compared with the QCD Monte Carlo models HERWIG, ISAJET, and PYTHIA. The models describe fairly well the multiplicity distribution of charged particles within the leading charged jet, the size of the leading charged jet, the radial distribution of charged particles and transverse momentum around the leading charged jet direction, and the momentum distribution of charged particles within the leading charged jet. The direction of the leading “charged particle jet” in each event is used to define three regions of η-φ space. The “toward” region contains the leading “charged particle jet,” while the “away” region, on the average, contains the away-side jet. The “transverse” region is perpendicular to the plane of the hard 2-to-2 scattering and is very sensitive to the “underlying event” component of the QCD Monte Carlo models. HERWIG, ISAJET, and PYTHIA with their default parameters do not describe correctly all the properties of the “transverse” region.

We report a measurement of the diffractive structure function F_jj^D of the antiproton obtained from a study of dijet events produced in association with a leading antiproton in p̅ p collisions at sqrt[s]  =  630 GeV at the Fermilab Tevatron. The ratio of F_jj^D at sqrt[s]  =  630 GeV to F_jj^D obtained from a similar measurement at sqrt[s]  =  1800 GeV is compared with expectations from QCD factorization and other theoretical predictions. We also report a measurement of the ξ ( x-Pomeron) and β ( x of parton in Pomeron) dependence of F_jj^D at sqrt[s]  =  1800 GeV. In the region 0.035<ξ<0.095, |t|<1 GeV², and β<0.5, F_jj^D(β,ξ) is found to be of the form β^-1.0±0.1ξ^-0.9±0.1, which obeys β-ξ factorization.

We present a detailed examination of the heavy flavor content of the W+jet data sample collected with the Collider Detector at Fermilab during the 1992–1995 collider run at the Fermilab Tevatron. Jets containing heavy flavor quarks are selected via the identification of secondary vertices or semileptonic decays of b and c quarks. There is generally good agreement between the rates of secondary vertices and soft leptons in the data and in the standard model simulation including single and pair production of top quarks. An exception is the number of events in which a single jet has both a soft lepton and a secondary vertex tag. In W+2,3 jet data, we find 13 such events where we expected 4.4±0.6 events. The kinematic properties of this small sample of events are statistically difficult to reconcile with the simulation of standard model processes.

We have searched for evidence of physics beyond the standard model in events that include an energetic photon and an energetic b-quark jet, produced in 85 pb^-1 of p̅ p collisions at 1.8 TeV at the Tevatron Collider at Fermilab. This signature, containing at least one gauge boson and a third-generation quark, could arise in the production and decay of a pair of new particles, such as those predicted by supersymmetry, leading to a production rate exceeding standard model predictions. We also search these events for anomalous production of missing transverse energy, additional jets and leptons (e, μ and τ), and additional b quarks. We find no evidence for any anomalous production of γb or γb+X events. We present limits on two supersymmetric models: a model where the photon is produced in the decay χ̃₂⁰→γχ̃₁⁰, and a model where the photon is produced in the neutralino decay into the gravitino LSP, χ̃₁⁰→γG̃. We also present our limits in a model-independent form and test methods of applying model-independent limits.

We present the first general search for new heavy particles, X, which decay via X→WZ⁰→eν+jj as a function of M_X and Γ(X) in pp̅ collisions at sqrt[s]  =  1.8 TeV. No evidence is found for production of X in 110 pb^-1 of data collected by the Collider Detector at Fermilab. General cross section limits are set at the 95% C.L. as a function of mass and width of the new particle. The results are further interpreted as mass limits on the production of new heavy charged vector bosons which decay via W^′→WZ⁰ in an extended gauge model as a function of the width, Γ(W^′), and mixing factor between the W^′ and the standard model W bosons.

We report a study of the decays B⁰→J/ψK^(*)0π⁺π^-, which involve the creation of a uu̅ or dd̅ quark pair in addition to a b̅ →c̅ (cs̅ ) decay. The data sample consists of 110 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8 TeV collected by the CDF detector at the Fermilab Tevatron collider during 1992–1995. We measure the branching fractions to be B(B⁰→J/ψK^*0π⁺π^-)  =  (6.6±1.9±1.1)×10^-4 and B(B⁰→J/ψK⁰π⁺π^-)  =  (10.3±3.3±1.5)×10^-4. Evidence is seen for contributions from ψ(2S)K^(*)0, J/ψK⁰ρ⁰, J/ψK^*+π^-, and J/ψK₁(1270).

We report a measurement of the strong coupling constant, α_s(M_Z), extracted from inclusive jet production in pp̅ collisions at sqrt[s]  =  1800 GeV. The QCD prediction for the evolution of α_s with jet transverse energy E_T is tested over the range 40<E_T<450 GeV using E_T for the renormalization scale. The data show good agreement with QCD in the region below 250 GeV. The value of α_s at the mass of the Z⁰ boson averaged over the range 40<E_T<250 GeV is found to be α_s(M_Z)  =  0.1178±0.0001(stat)_-0.0095^+0.0081(expt. syst). The associated theoretical uncertainties are mainly due to the choice of renormalization scale ({+6%}{-4%}) and input parton distribution functions (5%).

We have performed a search for gluinos (g̃) and scalar quarks (q̃) in a data sample of 84 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8 TeV, recorded by the Collider Detector at Fermilab. We investigate the final state of large missing transverse energy and three or more jets, a characteristic signature in R-parity-conserving supersymmetric models. The analysis has been performed “blind,” in that the inspection of the signal region is made only after the predictions from standard model backgrounds have been calculated. Comparing the data with predictions of constrained supersymmetric models, we exclude gluino masses below 195 GeV/c² ( 95% C.L.), independent of the squark mass. For the case m_q̃≈m_g̃, gluino masses below 300 GeV/c² are excluded.

We present a measurement of the cross section and the first measurement of the heavy flavor content of associated direct photon + muon events produced in hadronic collisions. These measurements come from a sample of 1.8 TeV pp̅ collisions recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily due to the Compton scattering process cg→cγ, with the final-state charm quark producing a muon. The cross section for events with a photon transverse momentum between 12 and 40 GeV/c is measured to be 46.8±6.3±7.5 pb, which is two standard deviations below the most recent theoretical calculation. A significant fraction of the events in the sample contain a final-state bottom quark. The ratio of charm to bottom production is measured to be 2.4±1.2, in good agreement with QCD models.

We present results of the first search for like-sign dilepton ( e^±e^±, e^±μ^±, μ^±μ^±) events associated with multijets and large missing energy using 106 pb^-1 of data in pp̅ collisions at sqrt[s]  =  1.8 TeV collected during 1992–1995 by the CDF experiment. Finding no events that pass our selection, we examine pair production of gluinos ( g̃) and squarks ( q̃) in a constrained framework of the minimal supersymmetric standard model. At tanβ  =  2 and μ  =  -800 GeV/c², we set 95% confidence level limits of M_g̃>221 GeV/c² for M_g̃≃M_q̃, and M_g̃>168 GeV/c² for M_q̃≫M_g̃, both with small variation as a function of μ.

We report the first observation of diffractive J/ψ(→μ⁺μ^-) production in p̅ p collisions at sqrt[s]  =  1.8 TeV. Diffractive events are identified by their rapidity gap signature. In a sample of events with two muons of transverse momentum p_T^μ>2 GeV/c within the pseudorapidity region |η|<1.0, the ratio of diffractive to total J/ψ production rates is found to be R_J/ψ  =  [1.45±0.25]%. The ratio R_J/ψ(x) is presented as a function of x-Bjorken. By combining it with our previously measured corresponding ratio R_jj(x) for diffractive dijet production, we extract a value of 0.59±0.15 for the gluon fraction of the diffractive structure function of the proton.

We present searches for quark-lepton compositeness and a heavy W^′ boson at high electron-neutrino transverse mass. We use ∼110 pb^-1 of data collected in pp̅ collisions at sqrt[s]  =  1.8 TeV by the CDF Collaboration during 1992–1995. The data are consistent with standard model expectations. Limits are set on the quark-lepton compositeness scale Λ, the ratio of partial cross sections σ(W^′→eν)/σ(W→eν), and the mass of a W^′ boson with standard model couplings. We exclude Λ<2.81 TeV and a W^′ boson with mass below 754 GeV/c² at the 95% confidence level. Combining with our previously published limit obtained using the muon channel, we exclude a W^′ boson with mass below 786 GeV/c² at the 95% confidence level.

We report on a measurement of the mean charged-particle multiplicity of jets in dijet events with dijet masses in the range 80–630 GeV/c², produced at the Tevatron in pp̅ collisions with sqrt[s]  =  1.8 TeV and recorded by the Collider Detector at Fermilab. The data are fit to perturbative-QCD calculations carried out in the framework of the modified leading log approximation and the hypothesis of local parton-hadron duality. The fit yields values for two parameters in that framework: the ratio of parton multiplicities in gluon and quark jets, r≡N_partons^g-jet/N_partons^q-jet  =  1.7±0.3, and the ratio of the number of charged hadrons to the number of partons in a jet, K_LPHD^charged≡N_hadrons^charged/N_partons  =  0.57±0.11.

We present results of searches for diphoton resonances produced both inclusively and also in association with a vector boson (W or Z) using 100 pb^-1 of pp̅ collisions using the CDF detector. We set upper limits on the product of cross section times branching ratio for both pp̅ →γγ+X and pp̅ →γγ+W/Z. Comparing the inclusive production to the expectations from heavy sgoldstinos we derive limits on the supersymmetry-breaking scale sqrt[F] in the TeV range, depending on the sgoldstino mass and the choice of other parameters. Also, using a NLO prediction for the associated production of a Higgs boson with a W or Z boson, we set an upper limit on the branching ratio for H→γγ. Finally, we set a lower limit on the mass of a “bosophilic” Higgs boson (e.g., one which couples only to γ, W, and Z bosons with standard model couplings) of 82 GeV/c² at 95% confidence level.

We present results from a measurement of double diffraction dissociation in p̅ p collisions at the Fermilab Tevatron collider. The production cross section for events with a central pseudorapidity gap of width Δη⁰>3 (overlapping η  =  0) is found to be 4.43±0.02(stat)±1.18(syst) mb [ 3.42±0.01(stat)±1.09(syst) mb] at sqrt[s]  =  1800[630] GeV. Our results are compared with previous measurements and with predictions based on Regge theory and factorization.