Measurements of the reaction e + e − → γ γ at center-of-mass energies in the range 6.2-7.4 GeV

Measurements of the cross section for the pair-annihilation reaction e/sup +/e/sup -/ ..-->.. ..gamma gamma.. at angles close to 90degree, relative to Bhabha scattering at 4degree, are reported at center-of-mass energies in the range 6.2--7.4 GeV. These measurements provide a fundamental test of quantum electrodynamics (QED) for spacelike values of the invariant four-momentum transfer q/sup 2/ as high at -40 (GeV/c)/sup 2/, which in this reaction is carried by the lepton propagator. A principal feature of the detection apparatus is the use of large NaI(Tl) total-absorption spectrometers. The results are in agreement with the predictions of QED.