122 research outputs found

    Measuring Bremsstrahlung Photons in 200 GeV p+p Collisions

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    Direct photon production is an important observable in heavy ion collisions as photons are penetrating and therefore largely insensetive to final state effects that lead to jet quenching. Measurements of the fragmentation component to prompt photon yields in p+p and Au+Au collisions will provide both an important test of pQCD predictions and of predictions for modifications of this component in heavy ion collisions. By selecting photons associated with jets on the near side using hadron-photon correlations, fragmentation photons can be measured directly.Comment: 5 pages, 4 figures, poster presented at the 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (QM2006

    Is a Large Intrinsic k_T Needed to Describe Photon + Jet Photoproduction at HERA?

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    We study the photoproduction of an isolated photon and a jet based on a code of partonic event generator type which includes the full set of next-to-leading order corrections. We compare our results to a recent ZEUS analysis in which an effective k_T of the incoming partons has been determined. We find that no additional intrinsic k_T is needed to describe the data.Comment: 23 pages LaTeX, 12 figure

    Isolated prompt photon photoproduction at NLO

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    We present a full next-to-leading order code to calculate the photoproduction of prompt photons. The code is a general purpose program of partonic event generator type with large flexibility. We study the possibility to constrain the photon structure functions and comment on isolation issues. A comparison to ZEUS data is also shown.Comment: 22 pages LaTeX, 15 figure

    A NLO calculation of the hadron-jet cross section in photoproduction reactions

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    We study the photoproduction of large-p_T charged hadrons in e p collisions, both for the inclusive case and for the case where a jet in the final state is also measured. Our results are obtained by a NLO generator of partonic events. We discuss the sensitivity of the cross section to the renormalisation and factorisation scales, and to various fragmentation function parametrisations. The possibility to constrain the parton densities in the proton and in the photon is assessed. Comparisons are made with H1 data for inclusive charged hadron production.Comment: 28 pages LaTeX, 14 figure

    A full Next to Leading Order study of direct photon pair production in hadronic collisions

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    We discuss the production of photon pairs in hadronic collisions, from fixed target to LHC energies. The study which follows is based on a QCD calculation at full next-to-leading order accuracy, including single and double fragmentation contributions, and implemented in the form of a general purpose computer program of "partonic event generator" type. To illustrate the possibilities of this code, we present the comparison with observables measured by the WA70 and D0 collaborations, and some predictions for the irreducible background to the search of Higgs bosons at LHC in the channel h→γγh \to \gamma \gamma. We also discuss theoretical scale uncertainties for these predictions, and examine several infrared sensitive situations which deserve further study.Comment: 45 pages Latex, 16 eps files plus some metafont files; replaced by the version to appear in Eur. Phys. J.

    Tools for NLO automation: extension of the golem95C integral library

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    We present an extension of the program golem95C for the numerical evaluation of scalar integrals and tensor form factors entering the calculation of one-loop amplitudes, which supports tensor ranks exceeding the number of propagators. This extension allows various applications in Beyond the Standard Model physics and effective theories, for example higher ranks due to propagators of spin two particles, or due to effective vertices. Complex masses are also supported. The program is not restricted to the Feynman diagrammatic approach, as it also contains routines to interface to unitarity-inspired numerical reconstruction of the integrand at the tensorial level. Therefore it can serve as a general integral library in automated programs to calculate one-loop amplitudes.Comment: 17 pages, 1 figure, the program can be downloaded from http://golem.hepforge.org/95/. arXiv admin note: substantial text overlap with arXiv:1101.559

    Next-To-Leading Order Determination of Fragmentation Functions

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    We analyse LEP and PETRA data on single inclusive charged hadron cross-sections to establish new sets of Next-to-Leading order Fragmentation Functions. Data on hadro-production of large-p⊥p_{\bot} hadrons are also used to constrain the gluon Fragmentation Function. We carry out a critical comparison with other NLO parametrizations

    Stable One-Dimensional Integral Representations of One-Loop N-Point Functions in the General Massive Case: I - Three Point Functions

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    In this article we provide representations for the one-loop three point functions in 4 and 6 dimensions in the general case with complex masses. The latter are part of the GOLEM library used for the computation of one-loop multileg amplitudes. These representations are one-dimensional integrals designed to be free of instabilites induced by inverse powers of Gram determinants, therefore suitable for stable numerical implementations.Comment: 40 pages, 1 figur
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