Wide-angle Compton Scattering at 8 and 10 GeV Photon Energies

We propose an experiment to measure the cross-section for Real Compton Scattering (RCS) from the proton in Hall C at incident photon energies of 8 GeV (s = 15.9 GeV) and 10 GeV (s = 19.6 GeV) over a broad span of scattering angles in the wide-angle regime. With 425 hours (18 days) of beam-time, high precision data in a previously unexplored kinematic regime will be obtained. The experiment will utilize an untagged bremsstrahlung photon beam and the standard cryogenic liquid hydrogen target. The scattered photon will be detected in the new NPS photon spectrometer, presently under construction in Hall C. The electron beam will pass through the target, while the electrons scattered in the direction of the calorimeter will be deflected by a small magnet which will allow for discrimination between the Compton and elastic electron scattering processes. The recoil protons will be detected in the Hall C HMS magnetic spectrometer. In the proposed experiment we will perform precise cross-section measurements at the highest possible photon energies over a broad kinematic range. These results will be essential in order to confirm whether the factorization regime has been attained and investigate the nature of the factorized reaction mechanism. Understanding this simplest of processes, which involves only two real photons and a single hadron, will provide a solid foundation for the understanding of other photo-induced exclusive reactions in the JLab energy range. Moreover, the universality of the underlying nucleon form-factors means that these data will be extremely valuable in understanding high momentum transfer data for two-photon exchange effects in elastic electron-nucleon scattering, time-like Compton scattering and other hard exclusive reactions. We have taken into account the PAC 40 recommendation to try to refocus the experiment in terms of the kinematic range, and to offer a very detailed explanation of how the proposed measurements will help lead to systematic improvements in the various theories of WACS. This is handled in Sec. 2.6, comprising one of the two major changes in the text since the first proposal. The other is a complete rewrite of the sections dealing with the simulation (Sec. 4.2) and in particular the sections describing the way data is actually going to be analyzed (Secs. 4.3 and 4.4).