Etude des Distributions de Parton Généralisées avec la Diffusion Compton Profondément Virtuelle 'genre espace' et 'genre temps'

摘要

More than forty years after the discovery of pointlike constituents inside the nucleon, its quarks and gluons structure is still intensively studied. Some exclusive processes (where all the final state products are known) of leptoproduction or of photoproduction of photon or meson off the nucleon provide access to the Generalized Parton Distributions (GPDs). These functions parameterize the complex structure of the nucleon and contain informations about the longitudinal momentum and the spatial transverse distribution of partons inside the nucleon. Such exclusive processes are the "Spacelike" and the "Timelike" Deeply Virtual Compton Scattering processes (DVCS and TCS respectively) which correspond to the scattering of a high-energy photon off a quark in the nucleon and are respectively measured in the reactions lN⇾l'N'γ (N = proton or neutron, l' = lepton) and γN⇾N'l+l-The first part of this thesis is devoted to the experimental study of DVCS, using the 2009 data from the COMPASS experiment at CERN. In a first step, the Deep Inelastic Scattering cross section is measured in order to check the muon flux measurement and to evaluate some systematic effects. Then, the cross section for the exclusive production of a photon is measured. It is made up of the DVCS process (the photon is emitted by a quark) and of the Bethe-Heitler process (the photon is emitted by the scattered lepton) which has the same final state. The study of the background has allowed to estimate in parallel an upper limit for the cross section of the exclusive production of a π° meson. The second part of the thesis is devoted to a phenomenological study of TCS at typical energies for the JLab 12 GeV upgrade. Firstly, the amplitudes for the TCS and for the associated Bethe-Heitler process are derived. Then, all single and double polarization (beam and/or target) observables are calculated as a function of different GPD contributions. Finally, a method is presented to extract the Compton Form Factors (functions of GPDs) from fits on DVCS and/or TCS data and/or simulations.