994 research outputs found

    Searches for Physics Beyond the Standard Model at Colliders

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    All experimental measurements of particle physics today are beautifully described by the Standard Model. However, there are good reasons to believe that new physics may be just around the corner at the TeV energy scale. This energy range is currently probed by the Tevatron and HERA accelerators and selected results of searches for physics beyond the Standard Model are presented here. No signals for new physics have been found and limits are placed on the allowed parameter space for a variety of different particles.Comment: Proceedings for 2007 Europhysics Conference on High Energy Physics, Manchester, July 200

    New angles on top quark decay to a charged Higgs

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    To properly discover a charged Higgs Boson (H¬ĪH^\pm) requires its spin and couplings to be determined. We investigate how to utilize \ttbar spin correlations to analyze the H¬ĪH^\pm couplings in the decay t‚ÜíbH+‚ÜíbŌĄ+őĹŌĄt\to bH^+\to b\tau^+\nu_\tau. Within the framework of a general Two-Higgs-Doublet Model, we obtain results on the spin analyzing coefficients for this decay and study in detail its spin phenomenology, focusing on the limits of large and small values for tan‚Ā°ő≤\tan\beta. Using a Monte Carlo approach to simulate full hadron-level events, we evaluate systematically how the H¬Ī‚ÜíŌĄ¬ĪőĹŌĄH^\pm\to\tau^\pm\nu_\tau decay mode can be used for spin analysis. The most promising observables are obtained from azimuthal angle correlations in the transverse rest frames of t(tňČ)t(\bar{t}). This method is particularly useful for determining the coupling structure of H¬ĪH^\pm in the large tan‚Ā°ő≤\tan\beta limit, where differences from the SM are most significant.Comment: 28 pages, 13 figures. Uses JHEP forma

    Study of Ző≥ events and limits on anomalous ZZő≥ and Ző≥ő≥ couplings in ppŐĄ collisions at s=1.96TeV

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    We present a measurement of the Ző≥ production cross section and limits on anomalous ZZő≥ and Ző≥ő≥ couplings for form-factor scales of őõ=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the eeő≥ (őľőľő≥) final state using 320(290)pb-1 of ppŐĄ collisions at s=1.96TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h10,30Z|<0.23, |h20,40Z|<0.020, |h10,30ő≥|<0.23, and |h20,40ő≥|<0.019 for őõ=1000GeV. ¬© 2005 The American Physical Society

    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

    Measurement of the ppbar to ttbar production cross section at sqrt(s)=1.96 TeV in the fully hadronic decay channel

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    A measurement of the top quark pair production cross section in proton anti-proton collisions at an interaction energy of sqrt(s)=1.96 TeV is presented. This analysis uses 405 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. Fully hadronic ttbar decays with final states of six or more jets are separated from the multijet background using secondary vertex tagging and a neural network. The ttbar cross section is measured as sigma(ttbar)=4.5 -1.9 +2.0 (stat) -1.1 +1.4 (syst) +/- 0.3 (lumi) pb for a top quark mass of m(t) = 175 GeV/c^2.Comment: 10 pages, 10 figures, submitted to Phys. Rev.