Multi-photon final states in e^+e^- collisions at sqrt{s} = 130-172 GeV
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The process e^+e^- -> gamma gamma (gamma) is studied using data recorded with the OPAL detector at LEP. The data sample corresponds to a total integrated luminosity of 25.38 pb^{-1} taken at centre-of-mass energies of 130-172 GeV. The measured cross-sections agree well with the expectation from QED. In a combined fit using data from all centre-of-mass energies, the angular distribution is used to obtain improved limits on the cut-off parameters: Lambda_+ > 195 GeV and Lambda_- > 210 GeV (95% CL). In addition, limits on non-standard e^+e^-gamma couplings and contact interactions, as well as a 95% CL mass limit for an excited electron, M_{e^*} > 194 GeV for an e^+e^-gamma coupling kappa = 1, are determined.
25 pages, LaTeX. uses a4p.sty, 9 eps figures included (plus in colour), submitted to Zeit. Phys. C
25 pages, LaTeX. uses a4p.sty, 9 eps figures included (plus in colour), submitted to Zeit. Phys. C