Data on Is and Ic in γ→p→pπ0π0 reveal cascade decays of N(1900) via N(1520)π

Abstract Photoproduction of two neutral pions off the proton is studied using linearly polarized photons, and the polarization observables I s and I c are measured for the first time. These two observables are unique to multi-meson final states; they characterize correlations between the linear photon polarization and the direction of outgoing single particles in photoproduction of three-body final states. The I s and I c distributions suggest that, in the 1.8 to 2.0 GeV mass region, the N ( 1520 ) 3 / 2 − π intermediate state is reached with reaction dynamics consistent with a dominant J P = 3 / 2 + wave. These data are included in the Bonn–Gatchina (BnGa) partial wave analysis which is based on a large variety of data; the analysis confirms a significant contribution from the reaction chain γ p → N ( 1900 ) 3 / 2 + → N ( 1520 ) 3 / 2 − π 0 → p π 0 π 0 .