The ratio of the elastic e + p to e − p scattering cross sections has been measured precisely, allowing the determination of the two-photon exchange contribution to these processes. This neglected contribution is believed to be the cause of the discrepancy between the Rosenbluth and polarization transfer methods of measuring the proton electromagnetic form factors. The experiment was performed at the VEPP-3 storage ring at beam energies of 1.6 and 1.0 GeV and at lepton scattering angles between 15 • and 105 • . The data obtained show evidence of a significant two-photon exchange effect. The results are compared with several theoretical predictions.

An internal-target technique was used to make the first measurements of the tensor analyzing power 7^20 of electron-deuteron elastic scattering in the four-momentum-transfer range of 2-3 fm _l . Polarized deuterium atoms were confined within a storage cell in the VEPP-3 electron storage ring in Novosibirsk to achieve a total target thickness of 3x 10 12 cm ~2, 15 times greater than was previously possible with an atomic-beam target alone. The results for T20 are in agreement with reasonable models of the deuteron wave function.

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