Formation of the pseudoscalars pi 0, eta, and eta ' in the reaction gamma gamma --> gamma gamma.

Abstract

The Crystal Ball detector has been used at the DORIS II storage ring at DESY to study the reaction e+e−→e+e−γ*γ*→e+e−γγ, where X is a narrow resonance with mass between 100 and 3000 MeV. Formation of π0, η, and η’ mesons is observed, and the following meson partial widths are obtained: Γπ0Γ0→γγ=7.7±0.5±0.5 eV, Γη−γγ=0.514±0.017±0.035 keV, and Γη’→γγ=4.7±0.5±0.5 keV. No other narrow resonances are observed, and upper limits are given for the product ΓX→γγBX→γγ. .AE