Photoproduction of eta mesons off protons at CB-ELSA

QCD-inspired models predict more states in the hadron mass spectrum than have been seen experimentally. Models show that some of these states should be observed in photoproduction experiments, thus providing a sensitive tool to study hadron properties. Baryon resonances have broad, overlapping widths. Photoproduction of $\eta$ mesons serves as an isospin filter; the $\eta$ meson has isospin $I=0$ and for this reason, isospin conservation guarantees that the N$\eta$ final state can only be reached via formation of N$^\ast$ resonances. Contributions from $\Delta^\ast$ states with $I=3/2$ are excluded. We used the Crystal-Barrel Detector (CsI(Tl) calorimeter) at ELSA to determine the cross-section of the reaction $\gamma p\to\eta p$ studying the $\eta$ in its two neutral decay modes ($\eta \to 3\pi^{0} \to 6\gamma$ and $\eta \rightarrow 2\gamma$) for photon incoming energies in the range of $E_{\gamma} = 850-3000$ MeV. In this experiment, the Two-Armed Photon Spectrometer (TAPS) was placed in the forward direction. This BaF$_2$ calorimeter serves as a fast trigger and increases the overall angular coverage to essentially the full $4\pi$ solid angle. We present differential cross sections for $\eta$ photoproduction off the proton for ($-1 < {\rm cos}\,\theta^{\rm cms}_\eta < 1$). Approximately 600,000 events have been identified. Preliminary results of a partial wave analysis are discussed.