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Background: Photoproduction of pion pairs allows to study sequential decaysof nucleon resonances via excited intermediate states. Such decays areimportant e.g. for states which in the quark model have both oscillatorsexcited and de-excite them in a two-step process. However, analyses ofmulti-meson final states is difficult and requires more than unpolarized crosssection measurements. Purpose: Experimental study and model analysis in view ofresonant contributions of target and beam-target polarization observables forthe reaction $\gamma p \to \pi^0 \pi^0 p$. Methods: Investigated were target(single) and beam-target (double) polarization asymmetries in dependence ofseveral parameters. The experiments were performed at the Mainz Microtron(MAMI) using circularly polarized photon beams and transversally polarizedsolid-state butanol targets. The reaction products were analyzed with theCrystal Ball and TAPS detectors. Results: Studied were the polarizationobservables Py (unpolarized beam, target polarized in y direction) and Px(circularly polarized beam, target polarized in x direction), which are similarto T (target asymmetry) and F (beam-target asymmetry) for single pionproduction. The asymmetries were analyzed with three independent methods,revealing systematic uncertainties.

Target and beam-target asymmetries for the $\gamma p \to \pi^0 \pi^0 p$ reaction