Bonn 2020 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 22: Hadron Structure and Spectroscopy V

HK 22.1: Group Report

Wednesday, April 1, 2020, 14:00–14:30, J-HS A

Truncated partial-wave analyses and complete experiments in pseudoscalar meson photoproduction — •Yannick Wunderlich — HISKP, Universität Bonn

The unravelling of the nucleon excitation spectrum poses a long lasting challenge on the way towards a precise understanding of bound-state formation in QCD. Experiments on the photoproduction of mesons have been performed, in order to find resonances which have escaped observations before. The photoproduction of a single pseudoscalar meson allows for the extraction of 16 polarization observables.

One can search for so-called "complete experiments", i.e. for minimal subsets of the 16 observables which still allow for an unambiguous determination of the underlying set of 4 spin-amplitudes. At least for studies of numerically precise pseudo-data, 8 carefully selected observables can form a complete experiment. The numerical extraction of the 4 spin-amplitudes is termed a complete experiment analysis (CEA).

In a truncated partial-wave analysis (TPWA), i.e. the extraction of a finite number of photoproduction multipoles from angular distributions of the data, fewer than 8 observables can be already sufficient. However, the apparent reduction of complete sets in the TPWA breaks down once one attempts to determine high multipoles from data with realistic error-bars. In this case, further constraints are needed.

The presentation will outline a new bipartite fit-method for the TPWA, which includes constraints from the results of a previously performed CEA. Preliminary results for an analysis of eta photoproduction (γ p —→ η p) will be shown.