We search for resonant production of tt¯ pairs in 4.8fb-1 integrated luminosity of pp¯ collision data at s=1.96TeV in the lepton+jets decay channel, where one top quark decays leptonically and the ...other hadronically. A matrix-element reconstruction technique is used; for each event a probability density function of the tt¯ candidate invariant mass is sampled. These probability density functions are used to construct a likelihood function, whereby the cross section for resonant tt¯ production is estimated, given a hypothetical resonance mass and width. The data indicate no evidence of resonant production of tt¯ pairs. A benchmark model of leptophobic Z'→tt¯ is excluded with mZ'<900GeV/c2 at 95% confidence level.
This paper reports a search for nonstandard model topquark resonances, Z', decaying to tt¯→W+bW-b¯, where both W decay to quarks. We examine the top-antitop quark invariant mass spectrum for the ...presence of narrow resonant states. The search uses a data sample of pp¯ collisions at a center of mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 2.8fb-1. No evidence for top-antitop quark resonant production is found. We place upper limits on the production cross section times branching ratio for a specific topcolor assisted technicolor model in which the Z' has a width of ΓZ'=0.012MZ'. Within this model, we exclude a Z' boson with masses below 805GeV/c2 at the 95% confidence level.
The fast track processor (FTK) has been proposed for high-quality track finding at very high rates (level-1 output rates) for the LHC experiments. Fast, efficient and precise pattern recognition has ...been studied using a silicon 6-layer sub-detector, including a subset of the pixel and SCT layers. We tested the FTK algorithms using the ATLAS full simulation. We compare the FTK reconstruction quality with the tracking capability of the offline iPatRec algorithm. We show that similar resolutions and efficiencies are reached by FTK at a speed higher than iPatRec by orders of magnitude. With FTK full events are reconstructed at the level-1 output rate. B s 0 rarrmu + mu - events are fully simulated together with background samples. We show that a low level-2 rate is allowed by FTK, even using a single 6 GeV level-1 muon selection trigger. FTK provides the full-resolution track list ready for the level-2 B s 0 identification. All selection cuts performed by the Event Filter can be easily anticipated at level-2. We present the B s 0 rarrmu + mu - efficiency gain and related level-2 rates.
We describe the architecture evolution of the highly-parallel dedicated processor FTK, which is driven by the simulation of LHC events at high luminosity (1034 cm-2 s-1). FTK is able to provide ...precise on-line track reconstruction for future hadronic collider experiments. The processor, organized in a two-tiered pipelined architecture, execute very fast algorithms based on the use of a large bank of pre-stored patterns of trajectory points (first tier) in combination with full resolution track fitting to refine pattern recognition and to determine off-line quality track parameters. We describe here how the high luminosity simulation results have produced a new organization of the hardware inside the FTK processor core.
The Fast Tracker (FTK) is a proposed upgrade to the ATLAS trigger system that will operate at full Level-1 output rates and provide high quality tracks reconstructed over the entire detector by the ...start of processing in Level-2. FTK solves the combinatorial challenge inherent to tracking by exploiting the massive parallelism of Associative Memories (AM) that can compare inner detector hits to millions of pre-calculated patterns simultaneously. The tracking problem within matched patterns is further simplified by using pre-computed linearized fitting constants and leveraging fast DSP's in modern commercial FPGA's. Overall, FTK is able to compute the helix parameters for all tracks in an event and apply quality cuts in approximately one millisecond. By employing a pipelined architecture, FTK is able to continuously operate at Level-1 rates without deadtime. The system design is defined and studied using ATLAS full simulation. Reconstruction quality is evaluated for single muon events with zero pileup, as well as WH events at the LHC design luminosity. FTK results are compared with the tracking capability of an offline algorithm.
The ttbar spin correlation at production is a fundamental prediction of QCD and a potentially incisive test of new physics coupled to top quarks. We measure the ttbar spin state in ppbar collisions ...at sqrt(s) = 1.96 TeV using 1001 candidate events in the lepton plus jets decay channel reconstructed in the CDF II detector. In the helicity basis, for a top-quark mass of 172.5 GeV/c^2, we find a spin correlation coefficient kappa = 0.60 +/- 0.50 (stat) +/- 0.16 (syst), consistent with the QCD prediction, kappa ~= 0.40.
In this paper we report a measurement of the ttbar production cross section in ppbar collisions at sqrt(s)=1.96 TeV using data corresponding to an integrated luminosity of 2.2fb-1 collected with the ...CDF II detector at the Tevatron accelerator. We select events with significant missing transverse energy and high jet multiplicity. This measurement vetoes the presence of explicitly identified electrons and muons, thus enhancing the tau contribution of ttbar decays. Signal events are discriminated from the background using a neural network, and heavy flavor jets are identified by a secondary-vertex tagging algorithm. We measure a ttbar production cross section of 7.99 +/- 0.55(stat) +/- 0.76(syst) +/- 0.46(lumi) pb, assuming a top mass m_top = 172.5 GeV/c^2, in agreement with previous measurements and standard model predictions.
We report the first observation of two Cabibbo-suppressed decay modes of the B0_s meson. Using a sample of p-pbar collisions at sqrt{s}=1.96 TeV corresponding to 5.9 fb-1 of integrated luminosity ...collected with the CDFII detector at the Fermilab Tevatron, we search for new B0_s decay modes in a sample of events containing J/psi to mu+ mu- decays. We reconstruct a B0_s to J/psi K*(892)0 signal with K^*(892)0 to K+ pi-, observing a yield of 151 +/- 25 events with a statistical significance of 8.0 sigma. We also reconstruct a B0_s to J/psi K0_S signal with K0_S to pi+ pi-, observing a yield of 64 +/- 14 events with a statistical significance of 7.2 sigma. From these yields, we extract the branching ratios B(B0_s -> J/psi K*(892)0)= (8.3 +/- 3.8) x 10{-5} and B(B0_s -> J/psi K0)= (3.5 +/- 0.8) x 10{-5}, where statistical, systematic and fragmentation fraction uncertainties are included in the combined uncertainty.
A measurement of the top-quark pair-production cross section in ppbar collisions at sqrt{s}=1.96 TeV using data corresponding to an integrated luminosity of 1.12/fb collected with the Collider ...Detector at Fermilab is presented. Decays of top-quark pairs into the final states e nu + jets and mu nu + jets are selected, and the cross section and the b-jet identification efficiency are determined using a new measurement technique which requires that the measured cross sections with exactly one and multiple identified b-quarks from the top-quark decays agree. Assuming a top-quark mass of 175 GeV/c^2, a cross section of 8.5+/-0.6(stat.)+/-0.7(syst.) pb is measured.
We report on a search for the flavor-changing neutral-current decay D0 \to {\mu}+ {\mu}- in pp collisions at \surd s = 1.96 TeV using 360 pb-1 of integrated luminosity collected by the CDF II ...detector at the Fermilab Tevatron collider. A displaced vertex trigger selects long-lived D0 candidates in the {\mu}+ {\mu}-, {\pi}+{\pi}-, and K-{\pi}+ decay modes. We use the Cabibbo-favored D0 \to K-{\pi}+ channel to optimize the selection criteria in an unbiased manner, and the kinematically similar D0 \to{\pi}+ {\pi}- channel for normalization. We set an upper limit on the branching fraction (D0 --> {\mu}+ {\mu}-) < 2.1 E-7 (3.0 E-7) at the 90% (95%) confidence level.
PDF
