833 research outputs found

    Resummed jet rates for heavy quark production in electron-positron annihilation

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    Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.Comment: Talk given by German Rodrigo at EPS2003 - Aachen, Germany, July 2003; 3 pages, 2 figure

    From B Modes to Quantum Gravity and Unification of Forces

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    It is commonly anticipated that gravity is subject to the standard principles of quantum mechanics. Yet some (including Einstein) have questioned that presumption, whose empirical basis is weak. Indeed, recently Freeman Dyson has emphasized that no conventional experiment is capable of detecting individual gravitons. However, as we describe, if inflation occurred, the Universe, by acting as an ideal graviton amplifier, affords such access. It produces a classical signal, in the form of macroscopic gravitational waves, in response to spontaneous (not induced) emission of gravitons. Thus recent BICEP2 observations of polarization in the cosmic microwave background will, if confirmed, provide empirical evidence for the quantization of gravity. Their details also support quantitative ideas concerning the unification of strong, electromagnetic, and weak forces, and of all these with gravity.Comment: 4 pages, no figures. v2: minor typos corrected, reference added. v3: very minor typo corrected. Winning entry in Gravity Research Foundation essay competitio

    Using Cosmology to Establish the Quantization of Gravity

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    While many aspects of general relativity have been tested, and general principles of quantum dynamics demand its quantization, there is no direct evidence for that. It has been argued that development of detectors sensitive to individual gravitons is unlikely, and perhaps impossible. We argue here, however, that measurement of polarization of the Cosmic Microwave Background due to a long wavelength stochastic background of gravitational waves from Inflation in the Early Universe would firmly establish the quantization of gravity.Comment: 4 pages, no figures, revised in response to referee's reports. Accepted for publication in PR

    W+n-jet predictions at NLO matched with a parton shower

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    The MC@NLO method as implemented in the Sherpa MC generator is presented using the production of W-bosons in conjunction with up to three jets as an example. Corresponding results computed at next-to leading order in QCD and including parton shower corrections are compared to recent experimental data from the Large Hadron Collider.Comment: 4 pages, 2 figures. To appear in the proceedings of DIS 201

    Next-to-leading order matrix elements and truncated showers

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    An algorithm is presented that combines the ME+PS approach to merge sequences of tree-level matrix elements into inclusive event samples with the POWHEG method, which combines exact next-to-leading order matrix elements with parton showers. The quality of the approach and its implementation in Sherpa are exemplified by results for e+e- annihilation into hadrons at LEP, for Drell-Yan lepton-pair production at the Tevatron and for Higgs-boson and W+W- production at LHC energies.Comment: 5 pages, 8 figures; To appear in the proceedings of Physics at the LHC 2010, DESY, Hamburg, 7-12 June 201

    Bottom-quark mass effects in associated production with ZZ and HH bosons

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    In this study, predictions obtained in the four and in the five flavour schemes are compared for two important processes involving heavy flavours at the LHC: the production of a ZZ or a Higgs boson in association with bb quarks. In particular we obtain predictions with \Sherpa's \MCatNLO implementation for the four--flavour scheme, treating the bb's as massive, and with multijet merging at leading and next-to leading order for the five--flavour scheme. While differences between the two schemes, at the inclusive level, are well understood from resummation of possibly large logs into the bb-PDFs, differences in shape present a major problem for experimental measurements. We make use of data for Z+b(bˉ)Z+b(\bar{b}) production at the 77 TeV LHC to exhibit strengths and weaknesses of the different approaches and we use these results to validate predictions for bb-associated Higgs-boson production at the 13 TeV Run II.Comment: Proceedings of XXV International Workshop on Deep-Inelastic Scattering and Related Subjects, 3-7 April 2017, University of Birmingham, UK. 10 pages, 6 figure

    Resummed jet rates with heavy quarks in electron-positron collisions

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    Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.Comment: Talk given by German Rodrigo at QCD@Work 2003 - Conversano, Italy, June 2003; 6 pages, three figure

    Using cosmology to establish the quantization of gravity

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    While many aspects of general relativity have been tested, and general principles of quantum dynamics demand its quantization, there is no direct evidence for that. It has been argued that development of detectors sensitive to individual gravitons is unlikely, and perhaps impossible. We argue here, however, that measurement of polarization of the Cosmic Microwave Background due to a long wavelength stochastic background of gravitational waves from Inflation in the Early Universe would firmly establish the quantization of gravity

    Matching Parton Showers and Matrix Elements

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    We compare different procedures for combining fixed-order tree-level matrix element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different implementations of the so-called CKKW scheme and one based on the so-called MLM scheme using different matrix element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.Comment: Proceedings of the "HERA and the LHC" workshop, CERN/DESY 2004/200
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