The reactions γp → ηp and γp → η 0 p are measured from their thresholds up to the center-of-mass energy W ¼ 1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η 0 threshold, W ¼ 1896 MeV (E γ ¼ 1447 MeV). Within the framework of a revised ηMAID isobar model, the cusp, in connection with a steep rise of the η 0 total cross section from its threshold, can only be explained by a strong coupling of the poorly known Nð1895Þ1=2 − state to both ηp and η 0 p. Including the new high-accuracy results in the ηMAID fit to available η and η 0 photoproduction data allows the determination of the Nð1895Þ1=2 − properties.

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Measurement of the ω → π 0 e + e − and η → e + e − γ Dalitz decays with the A2 setup at MAMI The Dalitz decays η → e + e − γ and ω → π 0 e + e − have been measured in the γp → ηp and γp → ωp reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the electromagnetic transition form factor of η, Λ −2 η = (1.97 ± 0.11tot ) GeV −2 , is in good agreement with previous measurements of the η → e + e − γ and η → µ + µ − γ decays. The uncertainty obtained in the value of Λ −2 η is lower than in previous results based on the η → e + e − γ decay. The value obtained for the ω slope parameter, Λ −2 ωπ 0 = (1.99 ± 0.21tot) GeV −2 , is somewhat lower than previous measurements based on ω → π 0 µ + µ − , but the results for the ω transition form factor are in better agreement with theoretical calculations, compared to earlier experiments.

The Dalitz decay π 0 → e + e − γ has been measured in the γp → π 0 p reaction with the A2 taggedphoton facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the π 0 electromagnetic transition form factor, aπ = 0.030 ± 0.010tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of aπ is lower than in previous results based on the π 0 → e + e − γ decay.

The Compton double-polarization observable 2z has been measured for the first time in the (1232) resonance region using a circularly polarized photon beam incident on a longitudinally polarized proton target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using either a dispersion relation calculation or a baryon chiral perturbation theory calculations with the weighted average of these two fits resulting in γ E 1E 1 = −2.87 ± 0.52, γ M1M1 = 2.70 ± 0.43, γ E 1M2 = −0.85 ± 0.72, and γ M1E 2 = 2.04 ± 0.43, in units of 10 −4 fm 4 .