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  • Observation of the p η ′ Cu...
    Afzal, F.; Wunderlich, Y.; Anisovich, A. V.; Bayadilov, D.; Beck, R.; Becker, M.; Blanke, E.; Brinkmann, K.-Th; Ciupka, S.; Crede, V.; Dieterle, M.; Dutz, H.; Elsner, D.; Friedrich, S.; Frommberger, F.; Gridnev, A.; Gottschall, M.; Grüner, M.; Gutz, E.; Hammann, C.; Hannappel, J.; Hartmann, J.; Hillert, W.; Hoff, J.; Hoffmeister, P.; Honisch, C.; Jude, T.; Kalinowsky, H.; Kalischewski, F.; Keshelashvili, I.; Klassen, P.; Klein, F.; Klempt, E.; Koop, K.; Kroenert, P.; Krusche, B.; Lang, M.; Lopatin, I.; Mahlberg, P.; Meißner, U.-G.; Messi, F.; Metag, V.; Meyer, W.; Mitlasóczki, B.; Müller, J.; Müllers, J.; Nanova, M.; Nikonov, K.; Nikonov, V.; Novinskiy, V.; Novotny, R.; Piontek, D.; Reicherz, G.; Richter, L.; Rönchen, D.; Rostomyan, T.; Salisbury, B.; Sarantsev, A.; Schaab, D.; Schmidt, C.; Schmieden, H.; Schultes, J.; Seifen, T.; Sokhoyan, V.; Sowa, C.; Spieker, K.; Stausberg, N.; Thiel, A.; Thoma, U.; Triffterer, T.; Urban, M.; Urff, G.; van Pee, H.; Walther, D.; Wendel, Ch; Wiedner, U.; Wilson, A.; Winnebeck, A.; Witthauer, L.

    Physical review letters, 10/2020, Letnik: 125, Številka: 15
    Journal Article

    Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W = 1748 MeV to W = 2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη′ threshold Eγ = 1447 MeV (W = 1896 MeV). The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N (1895)1/2− nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.