Abstract
Pseudoscalar meson photoproduction experiments lead the search for an expanded \(N^*\) spectroscopy that is required by lattice solutions of QCD. Extensive data have been collected with proton targets that can potentially over-determine the production amplitude and allow a search for weak resonances. In contrast, data on photoproduction from neutrons is drastically limited. Both are needed since the \(\gamma p N^*\) and \(\gamma n N^*\) photo-couplings to \(I=1/2\) states are different and provide complementary information on the mechanisms for resonance excitation. The main subtleties in experiments with an effective polarized neutron target are reviewed. The considerable impact of new polarization data on multipole analyses are discussed, using the example of recent \(\pi ^- p\) measurements of the beam-target helicity asymmetry (E) from polarized \({ HD}\) in CLAS at Jefferson Lab. New partial wave analyses incorporating these data have found significant changes in helicity amplitudes of some established resonances, and signatures of weak resonances that previously were observed only in hyperon decay channels.
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Work supported by the US Department of Energy, Office of Nuclear Physics Division, under contract DE-AC05-06OR23177 under which Jefferson Science Associates operate Jefferson Laboratory.
This article belongs to the Topical Collection “NSTAR 2017—The International Workshop on the Physics of Excited Nucleons”.
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Sandorfi, A.M. Spin Asymmetries and Helicity Amplitudes in Photo-Production from Polarized Neutrons. Few-Body Syst 60, 10 (2019). https://doi.org/10.1007/s00601-018-1478-4
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DOI: https://doi.org/10.1007/s00601-018-1478-4