We discuss the experimental issues confronting measurements of the Virtual Compton Scattering (VCS) reaction ep → epγ with electron beam energies 6–30 GeV. We specifically address the kinematics of Deeply Virtual Compton Scattering (Deep Inelastic Scattering, with coincident detection of the exclusive real photon nearly parallel to the virtual photon direction) and large transverse momentum VCS (High energy VCS of arbitrary Q 2 , and the recoil proton emitted with high momentum transverse to the virtual photon direction). We discuss the experimental equipment necessary for these measurements. For the DVCS, we emphasize the importance of the Bethe-Heitler – Compton interference terms that can be measured with the electron-positron (beam charge) asymmetry, and the electron beam helicity asymmetry.

2014 Nous décrivons un spectromètre de paires comportant des chambres à étincelles à lecture par magnétostriction utilisé pour étudier la matérialisation de photons dans le champ des électrons atomiques.Un calculateur Varian 620 i en ligne permet de stocker les données sur bandes magnétiques.

A new technique for the measurement of the opening angle of electron-position pairs produced by γ-rays in nuclear emulsion is described. The photon beam axis is normal to the emulsion plane, while in the classical method it will be parallel to that plane. For the scanning of the plates in our method one follows the two electron tracks in the emulsion by displacing the stage along a direction parallel to the beam axis. We show that such a technique eliminates most of the systematic errors found in other methods and that the measurement errors are smaller in our case. Results are given for measurements done on 15460 pairs.