The Mainz high-precision proton form factor measurement

par M. Jan Bernauer (Nuclear Physics Institute, Johannes Gutenberg University, MAINZ.)

vendredi 23 oct. 2009, 11:00 → 12:00 Europe/Paris

Salle 9111

New interest in the low Q^2 behavior of the form factors of the proton stems from recent, strongly deviating measurements of the proton charge radius by laser spectroscopy [1] and from a potential bump structure at a Q^2 around 0.2 to 0.3 (GeV/c)^2 [2]. A high precision measurement program covering the Q2-range from 0.003 (GeV/c)2 to 1 (GeV/c)2 has been carried out at the 3-spectrometer-facility at MAMI with the aim to determine the electric and magnetic form factor of the proton with an uncertainty below 1%. The dataset includes about 2000 separate measurements, spanning the scattering angles from below 20° to above 120° at six beam energies. The overlapping and redundant measurements of the cross section, simultaneous monitoring of the luminosity, combined with beam stabilization systems and additional current measurements enable excellent control over systematic uncertainties. Besides the standard Rosenbluth separation, the data are analyzed with a direct global fit of different form factor models to this extensive set of measured cross sections. In the talk, I will present main design ideas of the experiment, analysis techniques and preliminary results. [1] S. G. Karshenboim, Cand. J. Phys. 77 (1999) 241. [2] J. Friedrich, Th. Walcher, Eur. Phys. J. A 17 (2003) 607.