812 research outputs found

    Some Predators of Polyps of Chrysaora quinquecirrha (Scyphozoa, Semaeostomeae) in the Chesapeake Bay

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    Some invertebrate predators of polyps of Chrysaora quinquecirrha were identified. They included Caprella equilibra, Callipallene brevirostris, N eopanope texana sayi, Pagurus longicarpus, Libinia dubia, and Cratena pilata. Only C. pilata showed a preference over other possible prey organisms

    Supersymmetric Electroweak Corrections to Single Top Quark Production at the Fermilab Tevatron

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    We have calculated the O(αewMt2/MW2)O(\alpha_{ew} M_t^2/M_W^2) supersymmetric electroweak corrections to single top quark production via qqˉtbˉq\bar q' \to t\bar b at the Fermilab Tevatron in the minimal supersymmetric model. The supersymmetric electroweak corrections to the cross section are a few percent for tanβ>1tan \beta> 1, and can exceed 10% for tanβ<1tan\beta<1. The combined effects of SUSY electroweak corrections and the Yukawa corrections can exceed 10% for favorable parameter values, which might be observable at a high-luminosity Tevatron.Comment: 13 pages, 4 figures available at reques

    Ratios of BB and DD Meson Decay Constants in Relativistic Quark Model

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    We calculate the ratios of BB and DD meson decay constants by applying the variational method to the relativistic hamiltonian of the heavy meson. We adopt the Gaussian and hydrogen-type trial wave functions, and use six different potentials of the potential model. We obtain reliable results for the ratios, which are similar for different trial wave functions and different potentials. The obtained ratios show the deviation from the nonrelativistic scaling law, and they are in a pretty good agreement with the results of the Lattice calculations.Comment: 13 pages, 1 Postscript figur

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    Single top quark production as a probe of R-parity-violating SUSY at pp and p\bar p colliders

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    We investigate the ability of single top quark production via qq'-> squark->tb and q \bar q'->slepton->t\bar b at the LHC and Tevatron to probe the strength of R-parity violating couplings in the minimal supersymmetric model. We found that given the existing bounds on R-parity violating couplings, single top quark production may be greatly enhanced over that predicted by the standard model, and that both colliders can either discover R-parity violating SUSY or set strong constraints on the relevant R-parity violating couplings. We further found that the LHC is much more powerful than the Tevatron in probing the squark couplings, but the two colliders have comparable sensitivity for the slepton couplings.Comment: 15 pages, 4 figure

    Radiative Scalar Meson Decays in the Light-Front Quark Model

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    We construct a relativistic 3P0^3P_0 wavefunction for scalar mesons within the framework of light-front quark model(LFQM). This scalar wavefunction is used to perform relativistic calculations of absolute widths for the radiative decay processes(0++)γγ,(0++)ϕγ(0^{++})\to\gamma\gamma,(0^{++})\to\phi\gamma, and (0++)ργ(0^{++})\to\rho\gamma which incorporate the effects of glueball-qqˉq\bar{q} mixing. The mixed physical states are assumed to be f0(1370),f0(1500)f_0(1370),f_0(1500),and f0(1710)f_0(1710) for which the flavor-glue content is taken from the mixing calculations of other works. Since experimental data for these processes are poor, our results are compared with those of a recent non-relativistic model calculation. We find that while the relativistic corrections introduced by the LFQM reduce the magnitudes of the decay widths by 50-70%, the relative strengths between different decay processes are fairly well preserved. We also calculate decay widths for the processes ϕ(0++)γ\phi\to(0^{++})\gamma and (0^{++})\to\gamma\gamm involving the light scalars f0(980)f_0(980) and a0(980)a_0(980) to test the simple qqˉq\bar{q} model of these mesons. Our results of qqˉq\bar{q} model for these processes are not quite consistent with well-established data, further supporting the idea that f0(980)f_0(980) and a0(980)a_0(980) are not conventional qqˉq\bar{q} states.Comment: 10 pages, 4 figure

    Angular Distributions of Drell-Yan Lepton Pairs at the Tevatron: Order αs2\alpha_s^2 Corrections and Monte Carlo Studies

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    We investigate the angular distribution of the lepton pair in the process ppˉγ+X++Xp \bar{p} \rightarrow \gamma^{\ast} + X \rightarrow \ell^+\ell^- + X, where the virtual photon is produced at high transverse momentum. The angular distribution of the leptons is very sensitive to possible nonperturbative effects, such as a nontrivial vacuum structure of QCD, and offers a good chance to test such effects. We present complete O(αs2){\cal O}(\alpha_s^2) calculations of the decay lepton distributions in the lepton pair rest frame. An order O(αs){\cal O}(\alpha_s) Monte Carlo study of the lepton angular distributions, with acceptance cuts and energy resolution smearing applied to the leptons, is also presented.Comment: 26 pages (Revtex) plus 9 (uuencoded) postscript figures available as a compressed tar file at ftp://phenom.physics.wisc.edu/pub/preprints/madph-94-857-figs.tar.

    Search for a Higgs Boson Produced in Association with a W Boson in pbar-p Collisions at sqrt{s} = 1.96 TeV

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    We present a search for a standard model Higgs boson produced in association with a W boson using 2.7 1/fb of integrated luminosity of pbar-p collision data taken at sqrt{s} = 1.96 TeV. Limits on the Higgs boson production rate are obtained for masses between 100 GeV and 150 GeV. Through the use of multivariate techniques, the analysis achieves an observed (expected) 95% confidence level upper limit of 5.6 (4.8) times the theoretically expected production cross section for a standard model Higgs boson with a mass of 115 GeV.Comment: submitted to Phys. Rev. Let

    Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

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    The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

    Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda_b -> Lambda mu+ mu-

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    We report the first observation of the baryonic flavor-changing neutral current decay Lambda_b -> Lambda mu+ mu- with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses ppbar collisions data sample corresponding to 6.8fb-1 at sqrt{s}=1.96TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Lambda_b -> Lambda mu+ mu- are measured. We find B(Lambda_b -> Lambda mu+ mu-) = [1.73+-0.42(stat)+-0.55(syst)] x 10^{-6}. We also report the first measurement of the differential branching ratio of B_s -> phi mu+ mu- using 49 signal events. In addition, we report branching ratios for B+ -> K+ mu+ mu-, B0 -> K0 mu+ mu-, and B -> K*(892) mu+ mu- decays.Comment: 8 pages, 2 figures, 4 tables. Submitted to Phys. Rev. Let
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