SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Direct (prompt) photon production is a field of very high interest in hadron colliders. It provides probes to search for new phenomena and to test QCD predictions. In this article, two recent cross-section results for direct photon production using the full CDF Run II data set are presented: diphoton production and photon production in association with a heavy quark.
We present a measurement of the $Z \to b \bar b$ production cross section in $p \bar p$ collisions at $\sqrt{s}$ = 1.96 TeV . We use a data set of 5.46 fb -1 collected by the CDF experiment at the Tevatron collider during Run II using a dedicated trigger path which required a displaced vertex compatible with a $b$-hadron decay. A data-driven procedure is applied to estimate the dijet mass spectrum of the non-resonant multijet background. Using a similar strategy we set one of the most stringent upper limits on the production of a Higgs-like particle in association with $b$ quarks. We also set a limit on the inclusive SM $ H \to b \bar b$ .
A brief report of some recent experimental developments concerning the X, Y and Z charmoniumlike mesons states and other puzzling states from the BaBar, Belle, BESIII and CDF experiments is presented.
We report updated results by the CDF II collaboration on diffractive W and Z production and preliminary results from a study of rapidity gaps between very forward jets.
The vibrational spectra of group 12 difluorides, MF{sub 2} (M = Zn, Cd, Hg), were investigated via coupled cluster singles, doubles, and perturbative triples, CCSD(T), including core correlation, with a series of correlation consistent basis sets ranging in size from triple-zeta through quintuple-zeta quality, which were then extrapolated to the complete basis set (CBS) limit using a variety of extrapolation procedures. The explicitly correlated coupled cluster method, CCSD(T)-F12b, was employed as well. Although exhibiting quite different convergence behavior, the F12b method yielded the CBS limit estimates closely matching more computationally expensive conventional CBS extrapolations. The convergence with respect to basis set size was examined for the contributions entering into composite vibrational spectroscopy, including those from higher-order correlation accounted for through the CCSDT(Q) level of theory, second-order spin-orbit coupling effects assessed within four-component and two-component relativistic formalisms, and vibrational anharmonicity evaluated via a perturbative treatment. Overall, the composite results are in excellent agreement with available experimental values, except for the CdF{sub 2} bond-stretching frequencies compared to spectral assignments proposed in a matrix isolation infrared and Raman study of cadmium difluoride vapor species [Loewenschuss et al., J. Chem. Phys. 50, 2502 (1969); Givan and Loewenschuss, J. Chem. Phys. 72, 3809 (1980)]. These assignments are called into question in the light of the composite results.
Abstract The W mass determination at the Tevatron CDF experiment reported a deviation from the SM expectation at the 7 σ level. We discuss a few possible interpretations and their collider implications. We perform electroweak global fits under various frameworks and assumptions. We consider three types of electroweak global fits in the effective-field-theory framework: the S - T , S - T - , and eight-parameter flavor-universal one. We discuss the amounts of tensions between different measurements reflected in these fits and the corresponding shifts in central values of these parameters. With these electroweak fit pictures in hand, we present a few different classes of models and discuss their compatibility with these results. We find that while explaining the discrepancy, the single gauge boson extensions face strong LHC direct search constraints unless the is fermiophobic (leptophobic), which can be realized if extra vector fermions (leptons) mix with the SM fermions (leptons). Vector-like top partners can partially generate the needed shift to the electroweak observables. The compatibility with the top squark is also studied in detail. We find that the non-degenerate top squark soft masses enhance the needed operator coefficients, enabling an allowed explanation compatible with current LHC measurements. Overall, more theoretical and experimental developments are highly in demand to reveal the physics behind this discrepancy.
The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. After the observation of the Higgs boson, the last missing component of the model, the measurement of the W boson mass provides a stringent test of the model. A measurement of the W boson mass is presented, which used data corresponding to 8.8 fb$^{-1}$ of integrated luminosity, collected in proton-antiproton collisions at a 1.96 TeV center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately 4 million W boson candidates was used to obtain a Wboson mass of 80433.5±6.4$_{stat}$ ±6.9$_{syst}$ = 80433.5±9.4 MeV, the precision of which exceeds that of all previous measurements combined. This measurement is in significant tension with the standard model expectation.
We present status of a search for two rare of the Z boson, Z(0) -> J/I- l and Z(0) -> Upsilon l at CDF. The state of analysis is described at the time of this worksop.
We present the most recent CDF results on the measurements of the decay and production vertex of the top-quark. New results on forward-backward asymmetry in top-antitop events are presented. Also, recent measurements of the branching fractions of top-quark are discussed. Finally, measurements in single top events, where top-quark is produced through electroweak processes, are presented. Despite the much larger number of top events collected at the LHC, due to the symmetric initial state and the better signal-to-background ratio in specific channels, some results will be lasting heritage of the Tevatron.
We present a measurement of the top quark mass in the lepton+jets and dilepton channels of t$\bar{t}$ decays using the template method. The data sample corresponds to an integrated luminosity of 5.6 fb -1 of p$\bar{p}$ collisions at Tevatron with √s = 1.96 TeV, collected with the CDF II detector. The measurement is performed by constructing templates of three kinematic variables in the lepton+jets and two kinematic variables in the dilepton channel. The variables are two reconstructed top quark masses from different jets-to-quarks combinations and the invariant mass of two jets from the W decay in the lepton+jets channel, and a reconstructed top quark mass and m T2 , a variable related to the transverse mass in events with two missing particles, in the dilepton channel. The simultaneous fit of the templates from signal and background events in the lepton+jets and dilepton channels to the data yields a measured top quark mass of M top = 172.1±1.1 (stat)±0.9 (syst) GeV/c 2 .
We present a study of Bs0 decays to the CP-odd final state J/ψ f 0 (980) with J/ψ → µ + µ - and f 0 (980) → π + π - . Using pp̄ collision data with an integrated luminosity of 3.8 fb -1 collected by the CDF II detector at the Tevatron we measure a Bs0 lifetime of τ(B 0 s → J/ψ f 0 (980)) = 1.70 -0.11 +0.12 (stat) ± 0.03(syst) ps. This is the first measurement of the Bs0} lifetime in a decay to a CP eigenstate and corresponds in the standard model to the lifetime of the heavy Bs0 eigenstate. We also measure the product of branching fractions of B 0 s → J/ψ f 0 (980) and f 0 (980) → π + π - relative to the product of branching fractions of B 0 s → J/ψφ and φ→K + K - to be R f 0/ψ = 0.257 ± 0.020(stat) ± 0.014(syst), which is the most precise determination of this quantity to date.
This paper presents a search for standard model Higgs boson production in association with a W boson using events recorded by the CDF experiment in a data set corresponding to an integrated luminosity of 5.6 fb⁻¹. The search is performed using a matrix element technique in which the signal and background hypotheses are used to create a powerful discriminator. The discriminant output distributions for signal and background are fit to the observed events using a binned likelihood approach to search for the Higgs boson signal. We find no evidence for a Higgs boson, and 95% confidence level (C.L.) upper limits are set on σ(pp̄→WH)×B(H→bb¯). The observed limits range from 3.5 to 37.6 relative to the standard model expectation for Higgs boson masses between mH=100 GeV/c² and mH=150 GeV/c². The 95% C.L. expected limit is estimated from the median of an ensemble of simulated experiments and varies between 2.9 and 32.7 relative to the production rate predicted by the standard model over the Higgs boson mass range studied.
We extend the standard model to include a weak-triplet and color-octet scalar. This 'octo-triplet' field consists of three particles, two charged and one neutral, whose masses and renormalizable interactions depend only on two new parameters. The charged octo-triplet decay into a W boson and a gluon is suppressed by a loop factor and an accidental cancellation. Thus, the main decays of the charged octo-triplet may occur through higher-dimensional operators, mediated by a heavy vectorlike fermion, into quark pairs. For an octo-triplet mass below the tb¯ threshold, the decay into Wb b¯ through an off-shell top quark has a width comparable to that into cs¯ or cb¯. Pair production with one octo-triplet decaying to two jets and the other decaying to a W and two soft b jets may explain the dijet-plus-W excess reported by the CDF Collaboration. The same higher-dimensional operators lead to CP violation in B s -B¯ s mixing.
Production of the Υ(1S) meson in association with a vector boson is a rare process in the standard model with a cross section predicted to be below the sensitivity of the Tevatron. Observation of this process could signify contributions not described by the standard model or reveal limitations with the current nonrelativistic quantum-chromodynamic models used to calculate the cross section. We perform a search for this process using the full Run II data set collected by the CDF II detector corresponding to an integrated luminosity of 9.4 fb -1 . Our search considers the Υ→μμ decay and the decay of the W and Z bosons into muons and electrons. Furthermore, in these purely leptonic decay channels, we observe one ΥW candidate with an expected background of 1.2±0.5 events, and one ΥZcandidate with an expected background of 0.1±0.1 events. Both observations are consistent with the predicted background contributions. The resulting upper limits on the cross section for Υ+W/Zproduction are the most sensitive reported from a single experiment and place restrictions on potential contributions from non-standard-model physics.
We present a measurement of the top-quark mass in events containing two leptons (electrons or muons) with a large transverse momentum, two or more energetic jets, and a transverse-momentum imbalance. We use the full proton-antiproton collision data set collected by the CDF experiment during the Fermilab Tevatron Run II at center-of-mass energy √s = 1.96 TeV, corresponding to an integrated luminosity of 9.1 fb –1 . A special observable is exploited for an optimal reduction of the dominant systematic uncertainty, associated with the knowledge of the absolute energy of the hadronic jets. The distribution of this observable in the selected events is compared to simulated distributions of tt¯ dilepton signal and background. We measure a value for the top-quark mass of 171.5±1.9 (stat)±2.5 (syst) GeV/c 2 .
We present a measurement of the total WW and WZ production cross sections in $p\bar{p}$ collision at $\sqrt{s}$ = 1.96 TeV, in a final state consistent with leptonic W boson decay and jets originating from heavy-flavor quarks from either a W or a Z boson decay. This analysis uses the full data set collected with the CDF II detector during Run II of the Tevatron collider, corresponding to an integrated luminosity of 9.4 fb -1 . An analysis of the dijet mass spectrum provides 3.7σ evidence of the summed production processes of either WW or WZ bosons with a measured total cross section of σ WW+WZ = 13.7±3.9 pb. Independent measurements of the WW and WZ production cross sections are allowed by the different heavy-flavor decay patterns of the W and Z bosons and by the analysis of secondary-decay vertices reconstructed within heavy-flavor jets. The productions of WW and of WZ dibosons are independently seen with significances of 2.9σ and 2.1σ, respectively, with total cross sections of σ WW = 9.4±4.2 pb and σ WZ = 3.7$+2.5\atop{-2.2}$ pb. Lastly, the measurements are consistent with standard-model predictions.
We present a measurement of the top-quark width in the lepton+jets decay channel of tt events produced in pp collisions at Fermilab's Tevatron collider and collected by the CDF II detector. From a data sample corresponding to 4.3 fb{sup -1} of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of the hadronically decaying W boson that comes from the top-quark decay are reconstructed for each event and compared with templates of different top-quark widths ({Gamma}{sub t}) and deviations from nominal jet energy scale ({Delta}{sub JES}) to perform a simultaneous fit for both parameters, where {Delta}{sub JES} is used for the in situ calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95% confidence level (CL) of {Gamma}{sub t}<7.6 GeV and a two-sided 68% CL interval of 0.3 GeV<{Gamma}{sub t}<4.4 GeV for a top-quark mass of 172.5 GeV/c{sup 2}, which are consistent with the standard model prediction.
The latest CDF anomaly, the excess of dijet events in the invariant-mass window 120-160 GeV in associated production with a W boson, can be explained by a baryonic Z{sup '} model in which the Z{sup '} boson has negligible couplings to leptons. Although this Z{sup '} model is hardly subject to the Drell-Yan constraint from Tevatron, it is constrained by the dijet data from UA2 ({radical}(s)=630 GeV), and the precision measurements at LEP through the mixing with the SM Z boson. We show that under these constraints this model can still explain the excess in the M{sub jj{approx}}120-160 GeV window, as well as the claimed cross section {sigma}(WZ{sup '}){approx}4 pb. Implications at the Tevatron would be the associated production of {gamma}Z{sup '}, ZZ{sup '}, and Z{sup '}Z{sup '} with the Z{sup '}{yields}jj. We show that with tightened jet cuts and improved systematic uncertainties both {gamma}Z{sup '}{yields}{gamma}jj and ZZ{sup '}{yields}l{sup +}l{sup -}jj channels could be useful to probe this model at the Tevatron.