851 research outputs found

    Probabilistic Particle Flow Algorithm for High Occupancy Environment

    Full text link
    Algorithms based on the particle flow approach are becoming increasingly utilized in collider experiments due to their superior jet energy and missing energy resolution compared to the traditional calorimeter-based measurements. Such methods have been shown to work well in environments with low occupancy of particles per unit of calorimeter granularity. However, at higher instantaneous luminosity or in detectors with coarse calorimeter segmentation, the overlaps of calorimeter energy deposits from charged and neutral particles significantly complicate particle energy reconstruction, reducing the overall energy resolution of the method. We present a technique designed to resolve overlapping energy depositions of spatially close particles using a statistically consistent probabilistic procedure. The technique is nearly free of ad-hoc corrections, improves energy resolution, and provides new important handles that can improve the sensitivity of physics analyses: the uncertainty of the jet energy on an event-by-event basis and the estimate of the probability of a given particle hypothesis for a given detector response. When applied to the reconstruction of hadronic jets produced in the decays of tau leptons using the CDF-II detector at Fermilab, the method has demonstrated reliable and robust performance.Comment: Accepted by Nuclear Instruments and Methods

    Independent measurement of the top quark mass and the light- and bottom-jet energy scales at hadron colliders

    Get PDF
    A method for the simultaneous determination of the energy scales for b-quark jets and light jets, the jet energy resolution, and the top quark mass at hadron colliders is presented. The method exploits the unique kinematics of events with top-antitop pair production, where one of the top quarks involves a leptonic and one a hadronic W boson decay. The paper shows a feasibility study of how this simultaneous measurement can be performed at the upcoming LHC experiments ATLAS and CMS.Comment: 10 pages, 5 figure

    Search for B\u3csub\u3es\u3c/sub\u3e\u3csup\u3e0\u3c/sup\u3e→µ\u3csup\u3e+\u3c/sup\u3eµ\u3csup\u3e-\u3c/sup\u3e and B\u3csub\u3ed\u3c/sub\u3e\u3csup\u3e0\u3c/sup\u3e→µ\u3csup\u3e+\u3c/sup\u3eµ\u3csup\u3e-\u3c/sup\u3e Decays in \u3ci\u3ep\u3c/i\u3e\u3csup\u3eρ̅\u3c/sup\u3e Collisions with CDF II

    Get PDF
    We report on a search for Bs0→µ+µ- and Bd0→µ+µ- decays in pρ̅ collisions at √8=1.96 TeV using 364 pb-1 of data collected by the CDF II detector at the Fermilab Tevatron Collider. After applying all selection requirements, we observe no candidates inside the Bs0 or Bd0 mass windows. The resulting upper limits on the branching fractions are Ɓ (Bs0→µ+µ-)\u3c1.5×10-7 and Ɓ (Bd0→µ+µ-)\u3c3.9×10-8 at 90% confidence level

    B(Ds^+ -> l^+ nu) and the Decay Constant f_(D_s^+)

    Full text link
    I report final CLEO-c results on the purely leptonic decays of the D_s^+ -> l^+ nu, for the cases when l^+ is a mu^+ or tau^+, when it decays into pi^+ anti-nu, using 314/pb of data at 4.170 GeV. I also include preliminary results from the tau^+ -> e^+ nu anti-nu channel using 195/pb. Combining both we measure f_{D_s}= 275 +/- 10 +/- 5 MeV, and f_{D_s^+}/{f_{D^+}=1.24 +/- 0.10 =/- 0.03 .Comment: Presented at "The 2007 Europhysics Conference on High Energy Physics," Manchester, England, 19-25 July 2007, to appear in the proceedings. Three pages, 1 figur

    Review of Top Quark Physics Results

    Get PDF
    As the heaviest known fundamental particle, the top quark has taken a central role in the study of fundamental interactions. Production of top quarks in pairs provides an important probe of strong interactions. The top quark mass is a key fundamental parameter which places a valuable constraint on the Higgs boson mass and electroweak symmetry breaking. Observations of the relative rates and kinematics of top quark final states constrain potential new physics. In many cases, the tests available with study of the top quark are both critical and unique. Large increases in data samples from the Fermilab Tevatron have been coupled with major improvements in experimental techniques to produce many new precision measurements of the top quark. The first direct evidence for electroweak production of top quarks has been obtained, with a resulting direct determination of VtbV_{tb}. Several of the properties of the top quark have been measured. Progress has also been made in obtaining improved limits on potential anomalous production and decay mechanisms. This review presents an overview of recent theoretical and experimental developments in this field. We also provide a brief discussion of the implications for further efforts.Comment: 119 pages, 55 figure

    Evidence for the Exclusive Decay \u3ci\u3eB\u3c/i\u3e\u3csub\u3e\u3ci\u3ec\u3c/i\u3e\u3c/sub\u3e\u3csup\u3e±\u3c/sup\u3e → \u3ci\u3eJ\u3c/i\u3e/ψπ\u3csup\u3e±\u3c/sup\u3e and Measurement of the Mass of the \u3ci\u3eB\u3c/i\u3e\u3csub\u3e\u3ci\u3ec\u3c/i\u3e\u3c/sub\u3e\u3csup\u3e±\u3c/sup\u3e Meson

    Get PDF
    We report the first evidence for a fully reconstructed decay mode of the Bc± meson in the channel Bc± → 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 Bc± 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%

    Top-Quark Mass Measurement from Dilepton Events at CDF II

    Get PDF
    We report a measurement of the top-quark mass using events collected by the CDF II detector from pp̅ collisions at √s = 1.96 TeV at the Fermilab Tevatron. We calculate a likelihood function for the top-quark mass in events that are consistent with tt̅ → b̅ℓ-ν̅ℓbℓ′+ν′ℓ decays. The likelihood is formed as the convolution of the leading-order matrix element and detector resolution functions. The joint likelihood is the product of likelihoods for each of 33 events collected in 340 pb-1 of integrated luminosity, yielding a top-quark mass Mt = 165.2 ± 6.1(stat) ± 3.4(syst) GeV/c2. This first application of a matrix-element technique to tt̅ → bℓ+νℓb̅ℓ′-ν̅ℓ′ decays gives the most precise single measurement of Mt in dilepton events. Combined with other CDF run II measurements using dilepton events, we measure Mt = 167.9 ± 5.2(stat) ± 3.7(syst) GeV/c2

    Measurement of heavy-flavour production in proton-proton collisions at sqrt{s} = 7 TeV with ALICE

    Get PDF
    The measurement of the heavy-flavour production cross sections in pp collisions at the LHC will allow to test perturbative QCD calculations in a new energy domain. Moreover, within the physics program of the ALICE experiment, it will provide the reference for the study of medium effects in Pb-Pb collisions, where heavy quarks are regarded as sensitive probes of parton-medium interaction dynamics. We present the status and first preliminary results of charm and beauty production measurements with the ALICE experiment, using hadronic D meson decays and semi-leptonic D and B meson decays, including the first cross section measurement of muons from heavy flavour decays at forward rapidity. We also describe the preliminary cross section measurement for J/psi production, obtained using the di-electron decay channel at central rapidity and the di-muon decay channel at forward rapidity.Comment: 8 pages, 5 figures, proceedings of the conference HARD PROBES 2010, Eilat, October 201

    Search for B\u3csub\u3es\u3c/sub\u3e\u3csup\u3e0\u3c/sup\u3e→µ\u3csup\u3e+\u3c/sup\u3eµ\u3csup\u3e-\u3c/sup\u3e and B\u3csub\u3ed\u3c/sub\u3e\u3csup\u3e0\u3c/sup\u3e→µ\u3csup\u3e+\u3c/sup\u3eµ\u3csup\u3e-\u3c/sup\u3e Decays in \u3ci\u3ep\u3c/i\u3e\u3csup\u3eρ̅\u3c/sup\u3e Collisions with CDF II

    Get PDF
    We report on a search for Bs0→µ+µ- and Bd0→µ+µ- decays in pρ̅ collisions at √8=1.96 TeV using 364 pb-1 of data collected by the CDF II detector at the Fermilab Tevatron Collider. After applying all selection requirements, we observe no candidates inside the Bs0 or Bd0 mass windows. The resulting upper limits on the branching fractions are Ɓ (Bs0→µ+µ-)\u3c1.5×10-7 and Ɓ (Bd0→µ+µ-)\u3c3.9×10-8 at 90% confidence level

    Understanding the newly observed Y(4008) by Belle

    Full text link
    Very recently a new enhancement around 4.05 GeV was observed by Belle experiment. In this short note, we discuss some possible assignments for this enhancement, i.e. ψ(3S)\psi(3S) and DDˉD^*\bar{D}^* molecular state. In these two assignments, Y(4008) can decay into J/ψπ0π0J/\psi\pi^0\pi^0 with comparable branching ratio with that of Y(4008)J/ψπ+πY(4008)\to J/\psi\pi^+\pi^-. Thus one suggests high energy experimentalists to look for Y(4008) in J/ψπ0π0J/\psi\pi^0\pi^0 channel. Furthermore one proposes further experiments to search missing channel DDˉD\bar{D}, DDˉ+h.c.D\bar{D}^*+h.c. and especially χcJπ+ππ0\chi_{cJ}\pi^+\pi^-\pi^0 and ηcπ+ππ0\eta_c\pi^+\pi^-\pi^0, which will be helpful to distinguish ψ(3S)\psi(3S) and DDˉD^*\bar{D}^* molecular state assignments for this new enhancement.Comment: 4 pages, 5 figures. Typos correcte
    corecore