Double Polarization Observable E in η, π0 and 2π0 Photoproduction off Protons and Neutrons

Helicity dependent cross sections σ1/2, σ3/2, and the polarization observable E for π0, π0π0, and η photoproduction from quasi-free protons and neutrons in the second and third nucleon resonance region were measured for the first time at the electron accelerator facility MAMI. Different methods for the extraction of the observables were used to determine the systematics of the measurements. The results will provide stringent constraints on the resonances that contribute to the excitation spectrum of the nucleon and will clearly help to improve its theoretical understanding.