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HK: Fachverband Hadronen und Kerne

HK 46: Hadron Structure and Spectroscopy I

HK 46.2: Talk

Wednesday, March 18, 2009, 14:30–14:45, H-ZO 20

Helicity asymmetries in double pion photoproduction off deuterium — •Markus Oberle — Department of Physics, University of Basel

Recently, the measurement of the beam helicity asymmetry of pion pairs off the proton, using circularly polarized photon beams, has revealed surprising deficiencies in most reaction models for double pion production. With the present experiment a first attempt was made to measure such asymmetries also for photoproduction off the neutron, using a deuteron target. It was done at the Mainz MAMI accelerator for photon energies from 400 MeV to 1.5 GeV, using the combined Crystal Ball and TAPS electromagnetic calorimeters. In a first step the data for quasi-free protons were compared to free proton data. Good agreement indicates that the measurement is not seriously disturbed by nuclear Fermi motion. Very preliminary results seem to indicate that in the studied energy range, the asymmetries for n(γ,π⁰ π⁰)n are rather similar to p(γ,π⁰ π⁰)p.

Supported by Schweizerischer Nationalfond, DFG, and EU/FP6.