Observation of the p η ′ Cusp in the New Precise Beam Asymmetry Σ Data for γ p → p η

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 e...

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Veröffentlicht in:	Physical review letters 2020-10, Vol.125 (15), p.1-152002, Article 152002
Hauptverfasser:	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.
Format:	Artikel
Sprache:	eng
Schlagworte:	Asymmetry Baryons Cusps Eta-mesons Hadronic decays NUCLEAR PHYSICS AND RADIATION PHYSICS Photonuclear reactions Photoproduction Physics Protons Resonance Singularities
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Zusammenfassung:	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.
ISSN:	0031-9007 1079-7114
DOI:	10.1103/PhysRevLett.125.152002