532 research outputs found

    Photon pair production at flavour factories with per mille accuracy

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    We present a high-precision QED calculation, with 0.1% theoretical accuracy, of two photon production in e+ee^+ e^- annihilation, as required by more and more accurate luminosity monitoring at flavour factories. The accuracy of the approach, which is based on the matching of exact next-to-leading order corrections with a QED Parton Shower algorithm, is demonstrated through a detailed analysis of the impact of the various sources of radiative corrections to the experimentally relevant observables. The calculation is implemented in the latest version of the event generator BabaYaga, available for precision simulations of photon pair production at e+ee^+ e^- colliders of moderately high energies.Comment: 11 pages, 5 figures, 1 tabl

    Impact of QED corrections to Higgs decay into four leptons at the LHC

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    At the LHC a precise measurement of the Higgs boson mass (if discovered), at the level of 0.1-1%, will be possible through the channel g g --> H --> 4l for a wide range of Higgs mass values. To match such an accuracy, the systematic effects induced by QED corrections need to be investigated. In the present study the calculation of O(alpha) and higher order QED corrections is illustrated as well as their impact on the Higgs mass determination, once realistic event selection criteria for charged leptons and photons are considered.Comment: 5 pages, 5 figures, 1 table. Presented at HEP2005 July 21st-27th, 2005, Lisboa, Portugal and at RADCOR 2005, Shonan Village, October 2nd-7th, 2005, Japa

    Matrix elements and Parton Shower in the event generator BABAYAGA

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    A new version of the event generator BABAYAGA is presented, which is based on an original matching of the Parton Shower approach with the complete exact O(alpha) matrix element for the inclusion of the QED radiative corrections to the Bhabha process at flavour factories. The theoretical accuracy of the improved generator is conservatively estimated to be 0.2%, by comparison with independent calculations. The generator is a useful tool for precise luminosity determination at flavour factories, for center of mass energies below 10 GeV.Comment: 4 pages, 2 figures. To appear in the proceedings of the International Workshop e+ e- Collisions from phi to psi, Novosibirsk (Russia), 27 Feb - 2 Mar 200

    Multi-photon corrections to W boson mass determination at hadron colliders

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    The impact of higher-order final-state photonic corrections on the precise determination of the W-boson mass at the Tevatron and LHC colliders is evaluated. The W-mass shift from a fit to the transverse mass distribution is found to be about 10 MeV in the W --> mu nu channel and a few MeV in the W --> e nu channel. The calculation, which is implemented in the Monte Carlo event generator HORACE for data analysis, can contribute to reduce the uncertainty associated to the W mass measurement at present and future hadron collider experiments.Comment: 3 pages, 2 figures, to appear in the proceedings of International Europhysics Conference on High-Energy Physics (EPS 2003), Aachen, Germany, 17-23 Jul 200

    Precision electroweak calculation of the production of a high transverse-momentum lepton pair at hadron colliders

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    We present a detailed study of the production of a high transverse-momentum lepton pair at hadron colliders, which includes the exact O(alpha) electroweak corrections properly matched with leading logarithmic effects due to multiple photon emission, as required by the experiments at the Fermilab Tevatron and the CERN LHC. Numerical results for the relevant observables of single Z-boson production at hadron colliders are presented. The impact of the radiative corrections is discussed in detail. The presence in the proton of a photon density is considered and the effects of the photon-induced partonic subprocesses are analyzed. The calculation has been implemented in the new version of the event generator HORACE, which is available for precision simulations of the neutral and charged current Drell-Yan processes.Comment: October 2007, 22p

    A new approach to evaluate the leading hadronic corrections to the muon g-2

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    We propose a novel approach to determine the leading hadronic corrections to the muon g-2. It consists in a measurement of the effective electromagnetic coupling in the space-like region extracted from Bhabha scattering data. We argue that this new method may become feasible at flavor factories, resulting in an alternative determination potentially competitive with the accuracy of the present results obtained with the dispersive approach via time-like data.Comment: 7 pages, 3 figures. Version accepted for publication in Phys. Lett.

    Status and accuracy of the Monte Carlo generators for luminosity measurements

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    The status and accuracy of the precision Monte Carlo generators used for luminosity measurements at flavour factories is reviewed. It is shown that, thanks to a considerable, long-term effort in tuned comparisons between the predictions of independent programs, as well as in the validation of the generators against the presently available calculations of the next-to-next-to-leading order QED corrections to Bhabha scattering, the theoretical accuracy reached by the most precise tools is of about one per mille. This error estimate is valid for realistic experimental cuts, appears to be quite robust and is already sufficient for very accurate luminosity measurements. However, recent progress and possible advances to further improve it are also discussed.Comment: 6 pages, 1 table. Proceedings of the PhiPsi09 workshop, Oct. 13-16, 2009, Beijing, Chin
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