Measurement of polarization observables [Formula: see text] , [Formula: see text] , and [Formula: see text] in [Formula: see text] and [Formula: see text] photoproduction off quasi-free nucleons

The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive [Formula: see text] and [Formula: see text] photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the [Formula: see text] and [Formula: see text] reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the [Formula: see text] system at [Formula: see text] . A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the [Formula: see text] and [Formula: see text] resonances within the [Formula: see text] -partial wave.