Abstract : This thesis, divided into two parts, presents the calculation of radiative corrections to virtual Compton scattering (VSC) and describes the magnetic method (ARC project) adopted in the Hall A of Jefferson Lab. to measure the electron beam energy within an accuracy of 10-4.
Virtual Compton scattering experiments allow us to access to new proton observables: the generalized polarizabilities. As the extraction of those polarizabilities is made by comparing experimental and theoretical cross sections, systematical errors and radiative effects related to the experiments must be very accurately controlled. Therefore, a complete calculation of internal radiative corrections has been done in the frame work of quantum electrodynamics. This original calculation takes into account all graphs which contribution to the cross section is in alpha^4 except those related to proton radiation and to the exchange of two photons between leptonic and hadronic arms. The dimensional regularization method has been used for ultraviolet and infrared divergences treatment. After an addition-subtraction procedure, the infrared compensation is verified. Analytical calculation has been favored for the more internal integrals and then a specific numerical treatment has been employed for all other integrals. The results presented correspond to the different kinematics of VCS experiment which was held at TJNAF.
The method of absolute energy measurement we developed is based on the magnetic deviation composed of eight identical dipoles and leading the beam to the Hall A. The energy is determined from the measurement of the bending angle of the beam and from the measurement of the magnetic field integral along the deviation. The measurement of the bending angle is decomposed in a punctual measurement of a reference angle (by autocollimation) and in an on-line measurement of the deviations of the beam from that reference angle (four wire scanners are used). The absolute field integral along the deviation results from the punctual measurement of the relative field integral of the eight dipoles to a reference magnet and from the on-line measurement of that reference magnet.