München 2006 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 28: Elektromagnetische und Hadronische Sonden

HK 28.8: Talk

Wednesday, March 22, 2006, 15:45–16:00, F

Double Polarization Virtual Compton Scattering — •Luca Doria — Institut für Kernphysik, Johannes Gutenberg-Universität Mainz,Johann-Joachim-Becher-Weg 45,D-55099 Mainz,Germany

Virtual Compton Scattering (VCS) is, like Compton Scattering, a fundamental reaction in order to understand the physics of the nucleon, expecially in the nonperturbative regime of QCD. VCS off the proton consists in the reaction $∖gamma^{*} p ∖rightarrow p ∖gamma$, where $∖gamma^{*}$ and $∖gamma$ are the incoming virtual photon and the outgoing real photon respectively. With this reaction up to six new observables can be extracted: the Generalized Polarizabilities (GPs). Two of them represent the evolution of the ordinary nucleon polarizabilities as a function of the transferred momentum. VCS can be accessed experimentally measuring the reaction $ep ∖rightarrow ep∖gamma$. In an unpolarized in-plane measurement two combinations of GPs can be extracted. Using a polarized beam and measuring the recoil proton polarization one gains access to five GPs. In order to disentangle all the six GPs an out-of-plane measurement is also required. Currently the A1 Collaboration is carrying out the double polarization experiment with the final aim to extract all the six GPs at $Q^{2}=0.33$ $(GeV/c)^{2}$ using the polarized beam of the 100∖% duty-cycle Mainz Microtron (MAMI).