897 research outputs found

    Isolated Photons in Deep Inelastic Scattering

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    Photon radiation at large transverse momenta at colliders is a detailed probe of hard interaction dynamics. The isolated photon production cross section in deep inelastic scattering was measured recently by the ZEUS experiment, and found to be considerably larger than theoretical predictions obtained with widely used event generators. To investigate this discrepancy, we perform a dedicated parton-level calculation of this observable, including contributions from fragmentation and large-angle radiation. Our results are in good agreement with all aspects of the experimental measurement.Comment: 4 pages, 3 figure

    Matching NLLA+NNLO for event shape distributions

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    We study the matching of the next-to-leading logarithmic approximation (NLLA) onto the fixed next-to-next-to-leading order (NNLO) calculation for event shape distributions in electron-positron annihilation. The resulting theoretical predictions combine all precision QCD knowledge on the distributions, and are theoretically reliable over an extended kinematical range. Compared to previously available matched NLLA+NLO and fixed order NNLO results, we observe that the effects of the combined NLLA+NNLO are small in the three-jet region, relevant for precision physics.Comment: 14 pages, 18 figures; typos corrected, published versio

    e^+ e^- -> 3 jets and event shapes at NNLO

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    We report on the calculation of NNLO corrections to the 3-jet cross section and related event shape distributions in electron-positron annihilation. The corrections are sizable for all variables, however the magnitude of the corrections is substantially different for different observables. We observe that inclusion of the NNLO corrections yields a considerably better agreement between theory and experimental data both in shape and normalization of the event shape distributions in the region where the perturbative result is expected to hold. A new extraction of αs\alpha_{s} using the event shape variables up to NNLO yields a considerably better consistency between the observables indicating a stabilization of the perturbative corrections at this order.Comment: Contribution to the Proceedings of the 9th DESY workshop on "Loops and Legs in Quantum Field Theory", Sondershausen, April 200

    Estimation of the Compression Modulus of a Technical Rubber via Cyclic Volumetric Compression Tests

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    In many applications for ïŹnite element (FE) simulations rubber materials are assumed to be nearly incompressible by applying a high ratio between compression modulus and shear modulus. The compression modulus is commonly given as a constant value in FE analysis. In reality this assumption is not fully correct. InïŹ‚uencing factors like the compressibility of the included ïŹller can lead to a notably change of the compression modulus during mechanical loading. The focus of this work is on the estimation of the cyclic evolution of the compression modulus for a technical ethylene propylene diene rubber (EPDM) by using cyclic volumetric compression tests

    Determination of the strong coupling constant based on event shapes

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    We report on a determination of the strong coupling constant from a fit of QCD predictions for six event-shape variables, calculated at next-tonext-to-leading order (NNLO) and matched to resummation in the next-to-leadinglogarithmic approximation (NLLA). We use data collected by ALEPH at centre-ofmass energies between 91 and 206 GeV. We also investigate the role of hadronisation corrections, using both Monte Carlo generator predictions and analytic models to parametrise non-perturbative power corrections
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