Speaker
Description
One of the remaining challenges within the standard model is to gain a good
understanding of QCD in the non-perturbative regime. A key step towards this
aim is baryon spectroscopy, investigating the spectrum and the properties of
baryon resonances. To gain access to resonances with small
width, experiments with electromagnetic probes provide essential information.
Partial wave analyses need to be performed to extract the contributing
resonances. Here, a complete experiment is required to unambiguously determine
the contributing amplitudes. This involves the measurement of carefully chosen
single and double polarization observables.
In a joint endeavor by Jefferson Lab, MAMI, and ELSA, a new generation of experiments
with polarized beams, polarized proton and neutron targets, and
particle detection have been started in recent years. Many results of
unprecedented quality were recently published and included by the various
partial wave analysis groups in their analyses, leading to substantial
improvements, e.g. a more precise determination of resonance parameters. In
this talk, an overview of recent results is given, and their impact on our
understanding of the nucleon excitation spectrum is discussed.
