Complete QED NLO contributions to the reaction $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}\gamma$ and their implementation in the event generator PHOKHARA

Abstract

KLOE and Babar have an observed discrepancy of 2% to 5% in the invariant pion pair production cross section. These measurements are based on approximate NLO ${\mu }^{+}{\mu }^{-}\gamma$ cross section predictions of the Monte Carlo event generator PHOKHARA7.0. In this article, the complete NLO radiative corrections to ${\mu }^{+}{\mu }^{-}\gamma$ production are calculated and implemented in the Monte Carlo event generator PHOKHARA9.0. Numerical reliability is guaranteed by two independent approaches to the real and the virtual corrections. The novel features include the contribution of pentagon diagrams in the virtual corrections, which form a gauge-invariant set when combined with their box diagram partners. They may contribute to certain distributions at the percent level. Also the real emission was complemented with two-photon final state emission contributions not included in the generator PHOKHARA7.0. We demonstrate that the numerical influence reaches, for realistic charge-averaged experimental setups, not more than 0.1% at KLOE and 0.3% at BaBar energies. As a result, we exclude the approximations in earlier versions of PHOKHARA as origin of the observed experimental discrepancy.

28 pages, 8 figures

References in corpus (9)

• OneLOop: for the evaluation of one-loop scalar functions
• Measurement of sigma(e+ e- -> pi+ pi-) from threshold to 0.85 GeV^2 using Initial State Radiation with the KLOE detector
• Techniques for the calculation of electroweak radiative corrections at the one-loop level and results for W-physics at LEP200
• Narrow resonances studies with the radiative return method
• A complete algebraic reduction of one-loop tensor Feynman integrals
• A complete reduction of one-loop tensor 5- and 6-point integrals
• Simulation of electron-positron annihilation into hadrons with the event generator PHOKHARA
• Calculating contracted tensor Feynman integrals
• Reductions and Contractions of 1-loop Tensor Feynman Integrals

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