Measurement of the double polarization observable G in π[sup 0]-and η-photoproduction

The excitation spectrum of the proton consists of several strongly overlapping resonances, which are difficult to disentangle. To determine the exact contributions and identify these resonances, a solution of the partial wave analysis has to be found. For a complete experiment, which leads to an unambiguous solution, at least 8 well chosen single and double polarization observables are needed. With the new Crystal‐Barrel/TAPS experiment at ELSA, the measurement of double polarization parameters like E and G in different reactions is possible by using a circularly or linearly polarized photon beam on a longitudinally polarized butanol target. The Crystal‐Barrel/TAPS setup provides a nearly 4π angular coverage and a high detection efficiency for neutral states, which gives an ideal condition for the study of final state comprising neutral mesons. First preliminary results of the G asymmetry measurement in the reactions γ→p→→pπ0 and γ→p→→pη, which utilizes linearly polarized photons in combination with the l...