Abstract
Data and models on electromagnetic proton form factors are reviewed, highlighting the contribution foreseen by the PANDA collaboration. Electromagnetic hadron form factors contain essential information on the internal structure of hadrons. Precise and surprising data have been obtained at electron accelerators, applying the polarization method in electron-proton elastic scattering. At electron-positron colliders, using initial state radiation, BABAR measured proton time-like form factors in a wide time-like kinematical region and the BESIII collaboration will measure very precisely proton and neutron form factors in the threshold region. In the next future an antiproton beam with momentum up to 15 GeV/c will be available at FAIR (Darmstadt). Measurements of the reaction p̅ + p -> e^+ + e^- by the PANDA collaboration will contribute to the individual determination of electric and magnetic form factors in the time-like region of momentum transfer squared, as well as to their first determination in the unphysical region (below the kinematical threshold), through the reaction p̅ + p -> e^+ + e^- + pi^0. From the discussion on feasibility studies at PANDA, we focus on the consequences of such measurements in view of an unified description of form factors in the full kinematical region. We present models which have the necessary analytical requirements and apply to the data in the whole kinematical region.
Highlights
In future the PANDA collaboration [1] will make use of the antiproton beam of momentum up to 15 GeV/c at FAIR (Facility for Ions and Antiproton Research) [2] to study open problems related to non-perturbative Quantum Chromo Dynamics (QCD), the theory that drives the strong interaction
The kinematical domain which will be covered by PANDA is often called the transition or intermediate energy domain and the field of research "hadron physics", as in this energy range one can explore the internal structure of the hadron
The main challenge of the measurement of the reaction p + p → e+ + e− is the identification of the lepton pair in a huge hadronic background, in particular the production cross section of a charged pion pair, which is larger than the signal by six orders of magnitude and has very similar kinematics
Summary
In future the PANDA (antiProton Annihilation at Darmstadt) collaboration [1] will make use of the antiproton beam of momentum up to 15 GeV/c at FAIR (Facility for Ions and Antiproton Research) [2] to study open problems related to non-perturbative Quantum Chromo Dynamics (QCD), the theory that drives the strong interaction. We focus on the annihilation of pp into an electron pair through a virtual photon of momentum squared q2 = s (s is the total energy squared) which gives access to the hadron electromagnetic vertex γ∗ → pp (which is equivalent to γ∗ → pp, assuming charge invariance of the strong and electromagnetic interactions). In this case, q2 > 0, and this reaction (as well as the time reverse e+ + e− → p + p) gives access to the time-like (TL) region of momentum transfer squared.
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