EPJ A Highlight - Photocouplings at the Pole from Pion Photoproduction

Тelected fit results for the beam asymmetry Σ (left) and the double polarization E (right)

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.

Photocouplings at the pole from pion photoproduction, D. Rönchen et al. (2014), European Physical Journal A 50: 101, DOI 10.1140/epja/i2014-14101-3

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