210 research outputs found

    Four-pion production in tau decays and e+e- annihilation: an update

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    An improved description of four-pion production in electron-positron annihilation and in tau lepton decays is presented. The model amplitude is fitted to recent data from BaBar which cover a wide energy range and which were obtained exploiting the radiative return. Predicting tau decay distributions from e+e- data and comparing these predictions with ALEPH and CLEO results, the validity of isospin symmetry is confirmed within the present experimental errors. A good description of two- and three-pion sub-distributions is obtained. Special emphasis is put on the predictions for omega pi (-> pi+pi-pi0) in e+e- annihilation and in tau decay. The model amplitude is implemented in the Monte Carlo generator PHOKHARA.Comment: a few typos correcte

    Present status of precise calculation for small-angle Bhabha scattering

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    The problem of obtaining a theoretical description of Bhabha scattering at small angle, to monitor the luminosity at the precision 0 .1% requested by LEP experiments, is discussed and recent results are presented

    BHAGEN-1PH: A Monte Carlo event generator for radiative Bhabha scattering

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    BHAGEN-1PH is a FORTRAN program providing fast Monte Carlo event generation of the process e+e−→e+e−γe^+ e^- \to e^+ e^- \gamma, within electroweak theory, for both unpolarized beams and also for the longitudinally polarized electron beam. The program is designed for final leptons outside a small cone around the initial leptons direction and has a new algorithm allowing also for a fast generation of non collinear initial and final emission, as well as for asymmetric and different angular cuts for final leptons.Comment: 23 pages, plain Tex, no figure

    The Pseudothreshold Expansion of the 2-loop Sunrise Selfmass Master Amplitudes

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    The values at pseudothreshold of two loop sunrise master amplitudes with arbitrary masses are obtained by solving a system of differential equations. The expansion at pseudothreshold of the amplitudes is constructed and some lowest terms are explicitly presented.Comment: 1+22 pages, Latex, no figures, changes in Eq.(41),(44),(47

    Matching perturbative and Parton Shower corrections to Bhabha process at flavour factories

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    We report on a high-precision calculation of the Bhabha process in Quantum Electrodynamics, of interest for precise luminosity determination of electron-positron colliders involved in R measurements in the region of hadronic resonances. The calculation is based on the matching of exact next-to-leading order corrections with a Parton Shower algorithm. The accuracy of the approach is demonstrated in comparison with existing independent calculations and through a detailed analysis of the main components of theoretical uncertainty, including two-loop corrections, hadronic vacuum polarization and light pair contributions. The calculation is implemented in an improved version of the event generator BABAYAGA with a theoretical accuracy of the order of 0.1%. The generator is now available for high-precision simulations of the Bhabha process at flavour factories.Comment: 34 pages, 8 figures, uses elsart.cls. Version to appear on Nuclear Physics

    The Threshold Expansion of the 2-loop Sunrise Selfmass Master Amplitudes

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    The threshold behavior of the master amplitudes for two loop sunrise self-mass graph is studied by solving the system of differential equations, which they satisfy. The expansion at the threshold of the master amplitudes is obtained analytically for arbitrary masses.Comment: 1+18 pages, Latex, no figures, as in Journal reference with more changes in Eq.(31),(42),(45

    Numerical evaluation of the general massive 2-loop sunrise self-mass master integrals from differential equations

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    The system of 4 differential equations in the external invariant satisfied by the 4 master integrals of the general massive 2-loop sunrise self-mass diagram is solved by the Runge-Kutta method in the complex plane. The method, whose features are discussed in details, offers a reliable and robust approach to the direct and precise numerical evaluation of Feynman graph integrals.Comment: 1+21 pages, Latex, 5 ps-figure

    Extension and approximation of mm-subharmonic functions

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    Let Ω⊂Cn\Omega\subset \mathbb C^n be a bounded domain, and let ff be a real-valued function defined on the whole topological boundary ∂Ω\partial \Omega. The aim of this paper is to find a characterization of the functions ff which can be extended to the inside to a mm-subharmonic function under suitable assumptions on Ω\Omega. We shall do so by using a function algebraic approach with focus on mm-subharmonic functions defined on compact sets. We end this note with some remarks on approximation of mm-subharmonic functions

    Simulation of the process e+e−↦e+e−γe^+ e^- \mapsto e^+ e^- \gamma within electroweak theory with longitudinally polarized initial electrons

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    We present simple analytic expressions for the distributions of the Bhabha scattering process with emission of one hard photon, including weak boson exchanges, and with longitudinal polarization of the initial electron. The results from the Monte Carlo generator BHAGEN-1PH, based on these expressions, are presented and compared, for the unpolarized case, with those existing in literature.Comment: 9 pages, plain Tex, no figures, small change in Table
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