Baryon spectroscopy: Recent results from the Crystal Barrel∕TAPS experiment at ELSA

Abstract

To understand the spectrum and the properties of baryon resonances, the CBELSA/TAPS experiment at ELSA investigates the photoproduction of single‐ and multi‐meson final states off the nucleon. In the latter final states baryon cascades via Dp and Dh and also via higher mass baryon resonances are clearly observed. A partial wave analysis based on single and double meson photoproduction data as well as data from other reactions allows a first determination of resonance properties including partial decay widths of various N* and Δ* states. Those include also the decays into the different pπ0π0 and pπ0η decay channels resulting partly in unexpected results. Recently not only single but also double polarisation experiments have been performed, which are absolutelly necessary to resolve ambiguities in the partial wave analyses (PWA) used to extract the resonances from the data; without the measurement of polarisation observables a model‐independent PWA will not be possible. Polarisation observables have been investigated using linearly, circularly polarized or unpolarized photons impinging on an longitudinally polarized or unpolarized target. Given the angular coverage of the Crystal‐Barrel/TAPS experiment this data cover almost the full angular range and phase space. This data will provide key information for the partial wave analyses and brings us one step closer towards the needed complete experiment.