Study of Dimuon Production in Photon-Photon Collisions and Measurement of QED Photon Structure Functions at LEP

TL;DR

This study investigates muon pair production in photon-photon collisions at LEP1, testing QED predictions across a wide Q^2 range and measuring photon structure functions, including F_2^γ, F_A^γ, and F_B^γ, with results consistent with theoretical expectations.

Contribution

It provides the first detailed measurement of the photon structure functions F_2^γ, F_A^γ, and F_B^γ in photon-photon collisions at LEP1, validating QED predictions over a broad energy range.

Findings

QED predictions agree with measured distributions across Q^2 range

Measured ratios F_A^γ/F_2^γ and F_B^γ/F_2^γ differ from zero

Photon structure functions are consistent with theoretical models

Abstract

Muon pair production in the process e+e- -> 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.