Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP

Abstract

Muon pair production in the process $e^+e^-\to e^+e^-\mu^+\mu^-$ is studied using the data taken at LEP1 ( $\sqrt{s}\simeq m_Z$ ) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb $^{-1}$ . The QED predictions have been tested over the whole $Q^2$ range accessible at LEP1 (from several GeV $^2/c^4$ to several hundred GeV $^2/c^4$ ) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function $F_2^\gamma$ . Azimuthal correlations are used to obtain information on additional structure functions, $F_A^\gamma$ and $F_B^\gamma$ , which originate from interference terms of the scattering amplitudes. The measured ratios $F_A^\gamma/F_2^\gamma$ and $F_B^\gamma/F_2^\gamma$ are significantly different from zero and consistent with QED predictions.