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Measurement of polarization observables T , P , and H in π 0 and η photoproduction off quasi-free nucleons.

N JermannB KruscheV MetagF AfzalM BadeaR BeckP BielefeldtJ BielingM BirothE BlankeN BorisovM BornsteinK-T BrinkmannS CiupkaV CredeA DolzhikovP DrexlerH DutzD ElsnerA FedorovF FrommbergerS GardnerD GhosalS GoertzI GorodnovM GrünerC HammannJ HartmannW HillertP HoffmeisterC HonischT C JudeF KalischewskiB KetzerP KlassenF KleinE KlemptJ KnaustN KolanusJ KreitP KrönertM LangA B LazarevK LivingstonS LuttererP MahlbergC MeierW MeyerB MitlasoczkiJ MüllersM NanovaA NeganovK NikonovJ F NoëlM OstrickJ OttnadB OttoG PenmanT PollerD ProftG ReicherzN ReinartzL RichterS RunkelB SalisburyA V SarantsevD SchaabC SchmidtH SchmiedenJ SchultesT SeifenK SpiekerN StausbergM SteinacherF TaubertA ThielU ThomaA ThomasM UrbanG UrffY UsovH van PeeY C WangC WendelU WiednerY Wunderlichnull null
Published in: The European physical journal. A, Hadrons and nuclei (2023)
The target asymmetry T , recoil asymmetry P , and beam-target double polarization observable H were determined in exclusive π 0 and η photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the γ p → π 0 p and γ p → η p reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the η n system at W = 1.68 GeV . A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the S 11 ( 1535 ) and S 11 ( 1650 ) resonances within the S 11 -partial wave.
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