EPJ A Highlight - Photocouplings at the Pole from Pion Photoproduction

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Published on 01 July 2014

While the strong force is well understood at high energies in terms of perturbative QCD, the precise mechanism responsible for the confinement of quarks and gluons in color-neutral hadrons at low energies remains a mystery to date. The intermediate energy region is characterized by rich and complex spectra of excited baryons and mesons. Its phenomenology provides a key to our understanding of the fundamental properties of matter.

This theoretical interest has triggered large-scale experimental programs. Extracting the spectrum of baryon resonances from experimental data is a theoretical challenge, since the resonances are unstable and exhibit different decay patterns into different final states. Moreover, many resonances are broad and overlap in energy. Accordingly, a global multi-channel partial-wave analysis is required.

To this purpose, a theoretical model of meson-baryon interactions has been developed and resonance parameters were determined in the analysis of the reactions πN→πN, πN→ηN, πN→KΛ and πN→KΣ.

The present paper extends this analysis to single pion-photoproduction data - including over 20,000 measurements of cross sections and single- and double-polarization observables - from which the electromagnetic resonance properties are then extracted.