Scattering and annihilation electromagnetic processes

18 févr. 2013, 09:00 → 22 févr. 2013, 13:00 Europe/Rome

Trento ECT*

The electromagnetic structure of the hadrons can be described in terms of form factors. For a nucleon, two form factors are necessary to describe the charge and magnetic distributions. Form factors are considered fundamental quantities as their experimental values constitute a stringent test for any model which, after describing the static properties of a particle, like masses or magnetic moments should be also able to describe the dynamical *content*. They are measurable and data can be extracted from differential cross sections and polarization observables in elementary reactions. The basic tools to investigate hadron structure are the elementary processes electron proton elastic scattering, electron-positron annihilation into hadrons, and proton-antiproton annihilation into lepton pairs. New interest recently aroused due to the achievements in high energy accelerators: high intensity beams, high resolution spectrometers, full coverage detectors; but especially to the availability of polarized beams, targets and hadron polarimeters. A large experimental effort has been devoted to the determination of hadron form factors, at electron accelerators, as JLab, MAMI (Mainz), MIT-Bates on one side, at electron colliders as Novosibirsk, Frascati, Beijing (and also BaBar, Belle) and proton-antiproton rings (LEAR, FermiLab, and in next future, FAIR). Recent, very precise data from the GEp Collaboration at JLab, have been obtained using the polarization method, suggested many years ago by the Kharkov School (A.I. Akhiezer and M. P. Rekalo, 1967). These data have shown a decreasing of the ratio of electric to magnetic form factor of the proton, in disagreement with the previous data based on polarized cross section measurements (Rosenbluth method, 1950). As no shortcoming has been found in the experimental procedure, possible explanations have been suggested, which rely to radiative corrections at higher order, or to the reaction mechanism. The situation should still be clarified. BESIII is currently acquiring data in order to measure proton and neutron form factors in the time like region, in electron-positron annihilation into a nucleon-antinucleon pair, with energy scan and also using initial state radiation; the first results are expected soon. At PANDA (FAIR) full simulations with a realistic detector give promising results on the possibility to access form factors at very large values of the momentum transfer squared as well as in the unphysical region, when a pion is also emitted. The BESIII and PANDA form factors programs are somewhat complementary, the former accessing the threshold region, the latter probing asymptotic behavior. Although analytical considerations require that a unified description of form factors should be at the basis of the interpretation of all existing data, and fundamental symmetry properties of electromagnetic and strong interactions give prescriptions for a coherent description of annihilation and scattering channels, at least at lowest order of perturbation theory, the physics communities who work in these fields are quite dispersed. Large efforts are done in modeling the hadron structure and in interpreting the data in specific kinematic regions, but very few developments take in consideration the data in their globality. Therefore we find timely and necessary to gather the physicists working in the field of hadron structure, in order to emphasize and give priority and efforts to a satisfactory and complete description of the nucleon in the entire kinematical region. It is worth to note that the study of form factors has been initiated decades ago, and in the 60's in Italy and in Soviet Union, particularly, there were ideas in the directions we indicated above. Another aspect, which we would like to clarify and to revive for present and future experiments, is the problem of the reaction mechanism. We would like to focus the discussions during the workshop to the understanding of the interplay between the reaction mechanism and the hadron structure. The simple and elegant formalism that relates the matrix element and the form factors is based on the hypothesis of one photon exchange. At large values of the energy and momentum transfer achieved by modern experiments and due to the required precision, one has to take into account carefully radiative corrections. There are hints that higher order corrections could seriously affect the observables and those aspects should be coherently developed, in narrow connection with experimentalists.

lundi 18 février

09:00 → 12:30 Introductory Session

09:00 Registration

09:30 Opening

Orateur: Prof. WEISE Wolfram (ECT*)

09:45 Historical aspects of nucleon form factors

Orateur: Paola Ferretti-Dalpiaz (Universita di Ferrara)

10:40 Coffee Break

11:00 Experimental and theoretical aspects of nucleon form factors

Orateur: Prof. Rinaldo Baldini Ferroli (LNF, frascati)

11:45 Complementary views on nucleon structure from JLab and BES III to PANDA

Orateur: Prof. Frank Maas

12:30 → 14:30 Lunch Break

14:30 → 17:00 Radiative Corrections

14:30 Radiative Corrections to EM processes

Orateur: Prof. Victor S. Fadin

15:15 Application to experiments

Orateur: Dr Alexander GRAMOLIN

16:00 Coffee break

16:30 Methids, reactions, kinematics

Orateur: Dr Graziano Venanzoni

mardi 19 février

09:30 → 12:30 Nucleon models in time-like and space-like regions I

09:30 About physical meaning of Sachs FF

Orateur: Mikhail Galynskii

10:15 TBA

Orateur: Prof. Andrea Bianconi

10:45 Coffee Break

11:15 Constituent quarks

Orateur: Elena Santopinto

12:00 Interesting kinematical regions

Orateur: Dr Thierry Hennino

12:30 → 14:30 Lunch break

14:30 → 17:00 Nucleon Models in SL and TL regions II

14:30 Soliton models

Orateur: Dr Alessandro Drago

15:15 The light front constituent quark model and the EM properties of the nucleon

Orateur: Prof. Giovanni Salmè

16:00 Coffee break

16:30 From DIS to e+e- annihilation

Orateur: Prof. Marco Radici

mercredi 20 février

09:30 → 12:30 p-pbar annihilation

09:30 Nucleon Form Factor Experiments with 12 GeV at Jefferson Lab

Orateur: Dr Patrizia Rossi

10:15 Interpretation of TL-FFs

Orateur: Prof. Eduard Kuraev

10:45 Coffee break

11:15 ppbar-> mu+mu- X

Orateur: Dr Marco Destefanis

12:00 ppbar-> e+e- pi0

Orateur: Dr Yury Bystritskiy

12:30 → 14:30 Lunch

14:30 → 17:00 Crossed channels: ep elastic scattering

14:30 The form factors of the nucleon: present status

Orateur: Prof. Charles Perdrisat

15:15 Low energy ep scattering

Orateur: Prof. Hans Hammer

16:00 Coffee break

16:30 TBA

Orateur: Dr Bogdan Wojtsekhowski

jeudi 21 février

09:30 → 12:30 Crossed channel: e+e- annhilation

09:30 TBA

10:15 Study e+e- annihilation into nucleon-antinucleon pairs near threshold at VEPP-2000

Orateur: Prof. Vladimir Galubev

10:45 Coffee break

11:15 TBA

12:00 Fixed target experiments at the storage ring VEPP-3

Orateur: Prof. Dimitri Nikolenko

12:30 → 14:30 Lunch

14:30 → 17:15 Crossed channels: pe elastic scattering

14:30 Antiproton polarization

Orateur: Dr Paolo Lenisa

15:15 pe scattering applications

Orateur: M. Alaa Dbeyssi

15:45 Coffee break

16:15 Probing baryonic time-like electromagnetic transition form factors: results from the HADES experiments at GSI

16:45 Radiative corrections in ppbar in e+e-

Orateur: Dr Vladimir Bytev

vendredi 22 février

09:30 → 12:30 Furure projects

09:30 TL-FFs perspectives

Orateur: Prof. Diego Bettoni

10:10 FAIR perspectives

Orateur: Prof. Ulrich Wiedner

10:50 Coffee break

11:20 BESIII results

Orateur: Dr Monica Bertani

12:00 Conclusions