QED Test at LEP200 Energies in the Reaction $\rm e^+ e^-\to \gamma\gamma (\gamma)$

Abstract

The measurements of the QED reaction $ \EEGG $ performed with the L3 detector are used to search for new physics phenomena beyond the Standard Model. No evidence for these phenomena is found and new limits on their parameters are set. First the reaction is used to constrain a model of an excited electron and second to study contact interactions. The total and differential cross sections for the process $ \EEGG $, are measured at energies from 91 GeV to 202 GeV using the data collected with the L3 detector from 1991 to 1999. The L3 data set lower limits on the mass of an excited electron $ \MESTAR > 402 $ GeV, on the QED cutoff parameters $ \LAMP > 415 $ GeV, $ \LAMM > 258 $ GeV and on the contact interaction energy scale $ \Lambda > 1687 $ GeV. The last parameter limits the size of the interaction area to $ R < 1.17\times 10^{-17} $ cm. Some limits on the string and quantum gravity scales are also discussed.