"Unique Form of Continuity in Space"
by Umberto Boccioni

News...

• Proposal to measure nucleon form factors at a future, upgraded DAFNE facility: Letter of intent
• DAFNE Accelerator upgrade CDR

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Aim of the Workshop

is to discuss recent and new data on the form factors and their strangeness contribution as well as their theoretical interpretation and connection to GPD's. A special attention is also devoted to fostering current and future measurements, in particular to the proposal to separate the time like G_E and G_M form factors by measuring the center-of-mass angular distributions and polarization of the proton in reaction at the DAFNE storage ring upgraded in energy, or in the annihilationon a transversely polarized target, with the PAX experiment at the new GSI facility.

The form factors of the nucleon as measured in both the space-like and time-like domains provide information on the structure and dynamics of the nucleon. Both the analytical structure and phases of the form factors in the time-like regime are connected by dispersion relations to the space-like regime.

The recent experiments raised two serious issues: first the Fermilab E835 mesurements of |G_M(q²)| of the proton at q²=11.63 and 12.43 GeV² have shown that |G_M(q²)| in the time-like region is twice as large as in the space-like region; second, the studies of the electron-to-proton polarization transfer in electron proton scattering at Jlab show that the ratio of the electric to magnetic form factor of the proton |G_E(q²)|/|G_M(q²)| is monotonically decreasing with increasing Q²=-q², in strong contradiction with the ratio scaling derived in the traditional Rosenbluth separation method.

The knowledge of the phase difference between G_E and G_M may strongly constrain the models for both form factors. Despite the fundamental implications of the phases for an understanding of the connection between the space-like and time-like form factors, such measurements have never been made. Also the available data on |G_M^P| in the time-like region are scarce.

We would like that all scientists active in the field participate into the meeting. We are planning for about 60 physicists to attend the Workshop but can accommodate many more. We would reserve ample time for discussion both at the end of the presentations and between the sessions, so that one can progress on the open points and eventually express a strong scientific support for future measurements. The format of the workshop, with no written proceedings, is meant to encourage presentations and discussions of even very preliminary results.