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Photoproduction of $\pi\eta$-pairs from nucleons has been investigated fromthreshold up to incident photon energies of $\approx$~1.4~GeV. The quasi-freereactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$,$\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ were forthe first time measured from nucleons bound in the deuteron. The correspondingreactions from a free-proton target were also studied to investigatefinal-state interaction effects (for neutral pions the free-proton resultscould be compared to previous measurements; the $\gamma p\rightarrown\pi^+\eta$ reaction was measured for the first time). For the $\pi^0\eta$final state coherent production via the $\gamma d\rightarrow d\pi^0\eta$reaction was also investigated. The experiments were performed at the taggedphoton beam of the Mainz MAMI accelerator using an almost $4\pi$ coverageelectromagnetic calorimeter composed of the Crystal Ball and TAPS detectors.The total cross sections for the four different final states obey the relation$\sigma(p\pi^0\eta)$ $\approx$ $\sigma(n\pi^0\eta)$ $\approx$$2\sigma(p\pi^-\eta)$ $\approx$ $2\sigma(n\pi^+\eta)$ as expected for adominant contribution from a$\Delta^{\star}\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ reaction chain,which is also supported by the shapes of the invariant-mass distributions ofnucleon-meson and $\pi$-$\eta$ pairs. The experimental results are compared tothe predictions from an isobar reaction model.

The isospin structure of photoproduction of pi-eta pairs from the nucleon in the threshold region