Time-Like Electromagnetic Form Factors at Panda-FAIR

Abstract : At the accelerator complex FAIR (Darmstadt, Germany) a program of measurements of electromagnetic proton form factors is foreseen in the time-like region, with the detector PANDA. The high intensity and high energy antiproton beams will open the possibility to determine these form factors in a wide kinematical range, through the annihilation reaction $ p+\bar p\to e^++e^-$. The status of the proposed experiment as well as the expected results will be presented on the basis of realistic simulations. The impact of these measurements on the understanding of the nucleon structure and of the reaction mechanism will be discussed. At moderate values of the momentum transfer squared, $q^2$ the individual determination of the electric and magnetic FFs will strongly constrain the nucleon models, whereas at larger $q^2$ the validity of asymptotic properties predicted by QCD will be tested. These data, together with the information from the space-like region, will provide the experimental ground for a unified view of the electromagnetic structure of the proton as observed in scattering and annihilation reactions.