TA-CON-2014-004

Title
Proton electromagnetic form factors: present status and future perspectives at PANDA

Author:

E. Tomasi-Gustafsson
on behalf of the PANDA Collaboration

Address
CEA, IRFU, SPhN, Saclay, 91191 Gif-sur-Yvette Cedex, France and
CNRS/IN2P3, Institut de Physique Nucl\'eaire, UMR 8608, 91406 Orsay, France

Abstract

Electromagnetic FFs are fundamental quantities, which describe the internal structure of hadrons and the dynamic behaviour of their charge and magnetic distributions. Although experiments and theories develop since decades, recent experimental advances have driven an intensive and renewed activity in the field.

The development of high intensity, high polarized electron beams, large solid angle spectrometers and proton and neutron polarimeters in the GeV range opened the possibility to apply the polarization method suggested in the 70's by the Kharkov School and obtain precise and surprising data at electron accelerators.

At electron-positron facilities, using initial state radiation, BABAR measured FFs in a wide time-like kinematical region and the BES collaboration will measure very precisely proton and neutron FFs in the threshold region.

In next future an antiproton beam with momentum up to 15 GeV/c will be available at FAIR (Darmstadt) and measurements by the PANDA collaboration of proton-antiproton annihilation into an electro-positron pair should allow a precise measurement of electric and magnetic FFs in the time-like region in a wide region of momentum transfer. The emission of an additional pion will allow for the first time to access the unphysical region, below the kinematical threshold.

We will show the results of feasibility studies at PANDA and focus on the consequences of such measurements in view of a unified description of FFs in the full kinematical region. We will present models which have the necessary analytical requirements to apply in the whole kinematical region.