Observation of the pη^{'} Cusp in the New Precise Beam Asymmetry Σ Data for γp→pη

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

doi:10.1103/PhysRevLett.125.152002

Observation of the pη^{'} Cusp in the New Precise Beam Asymmetry Σ Data for γp→pη

Phys Rev Lett. 2020 Oct 9;125(15):152002. doi: 10.1103/PhysRevLett.125.152002.

Authors

F Afzal¹, Y Wunderlich¹, A V Anisovich^{1

2}, D Bayadilov^{1

2}, R Beck¹, M Becker¹, E Blanke¹, K-Th Brinkmann³, S Ciupka¹, V Crede⁴, M Dieterle⁵, H Dutz⁶, D Elsner⁶, S Friedrich³, F Frommberger⁶, A Gridnev², M Gottschall¹, M Grüner¹, E Gutz³, C Hammann¹, J Hannappel⁶, J Hartmann¹, W Hillert⁶, J Hoff¹, P Hoffmeister¹, C Honisch¹, T Jude⁶, H Kalinowsky¹, F Kalischewski¹, I Keshelashvili⁵, P Klassen¹, F Klein⁶, E Klempt¹, K Koop¹, P Kroenert¹, B Krusche⁵, M Lang¹, I Lopatin², P Mahlberg¹, U-G Meißner^{1

7}, F Messi⁶, V Metag³, W Meyer⁸, B Mitlasóczki¹, J Müller¹, J Müllers¹, M Nanova³, K Nikonov^{1

2}, V Nikonov^{1

2}, V Novinskiy², R Novotny³, D Piontek¹, G Reicherz⁸, L Richter¹, D Rönchen¹, T Rostomyan⁵, B Salisbury¹, A Sarantsev^{1

2}, D Schaab¹, C Schmidt¹, H Schmieden⁶, J Schultes¹, T Seifen¹, V Sokhoyan¹, C Sowa⁸, K Spieker¹, N Stausberg¹, A Thiel¹, U Thoma¹, T Triffterer⁸, M Urban¹, G Urff¹, H van Pee¹, D Walther¹, Ch Wendel¹, U Wiedner⁸, A Wilson^{1

4}, A Winnebeck¹, L Witthauer⁵; CBELSA/TAPS Collaboration

Affiliations

¹ Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Germany.
² National Research Centre "Kurchatov Institute", Petersburg Nuclear Physics Institute, Gatchina, Russia.
³ II. Physikalisches Institut, Universität Giessen, Germany.
⁴ Department of Physics, Florida State University, Tallahassee, Florida 32306, USA.
⁵ Physikalisches Institut, Universität Basel, Switzerland.
⁶ Physikalisches Institut, Universität Bonn, Germany.
⁷ Institute for Advanced Simulation, Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich, Germany.
⁸ Institut für Experimentalphysik I, Ruhr Universität Bochum, Germany.

PMID: 33095637
DOI: 10.1103/PhysRevLett.125.152002

Abstract

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 [E_{γ}=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.