Measurement of polarization observables [Formula: see text], [Formula: see text], and [Formula: see text] in [Formula: see text] and [Formula: see text] photoproduction off quasi-free nucleons

N Jermann; B Krusche; V Metag; F Afzal; M Badea; R Beck; P Bielefeldt; J Bieling; M Biroth; E Blanke; N Borisov; M Bornstein; K-T Brinkmann; S Ciupka; V Crede; A Dolzhikov; P Drexler; H Dutz; D Elsner; A Fedorov; F Frommberger; S Gardner; D Ghosal; S Goertz; I Gorodnov; M Grüner; C Hammann; J Hartmann; W Hillert; P Hoffmeister; C Honisch; T C Jude; F Kalischewski; B Ketzer; P Klassen; F Klein; E Klempt; J Knaust; N Kolanus; J Kreit; P Krönert; M Lang; A B Lazarev; K Livingston; S Lutterer; P Mahlberg; C Meier; W Meyer; B Mitlasoczki; J Müllers; M Nanova; A Neganov; K Nikonov; J F Noël; M Ostrick; J Ottnad; B Otto; G Penman; T Poller; D Proft; G Reicherz; N Reinartz; L Richter; S Runkel; B Salisbury; A V Sarantsev; D Schaab; C Schmidt; H Schmieden; J Schultes; T Seifen; K Spieker; N Stausberg; M Steinacher; F Taubert; A Thiel; U Thoma; A Thomas; M Urban; G Urff; Y Usov; H van Pee; Y C Wang; C Wendel; U Wiedner; Y Wunderlich; CBELSA/TAPS Collaboration

doi:10.1140/epja/s10050-023-01134-0

Measurement of polarization observables $T$ , $P$ , and $H$ in $π^{0}$ and $η$ photoproduction off quasi-free nucleons

Eur Phys J A Hadron Nucl. 2023;59(10):232. doi: 10.1140/epja/s10050-023-01134-0. Epub 2023 Oct 17.

Authors

N Jermann^{1

2}, B Krusche¹, V Metag³, F Afzal², M Badea², R Beck², P Bielefeldt², J Bieling², M Biroth⁴, E Blanke², N Borisov⁵, M Bornstein⁶, K-T Brinkmann³, S Ciupka², V Crede⁷, A Dolzhikov⁵, P Drexler⁴, H Dutz⁶, D Elsner⁶, A Fedorov⁵, F Frommberger⁶, S Gardner⁸, D Ghosal^{1

9}, S Goertz⁶, I Gorodnov⁵, M Grüner², C Hammann², J Hartmann², W Hillert^{6

10}, P Hoffmeister², C Honisch², T C Jude⁶, F Kalischewski², B Ketzer², P Klassen², F Klein⁶, E Klempt², J Knaust², N Kolanus², J Kreit², P Krönert², M Lang², A B Lazarev⁵, K Livingston⁸, S Lutterer^{1

11}, P Mahlberg², C Meier¹, W Meyer¹², B Mitlasoczki², J Müllers², M Nanova³, A Neganov⁵, K Nikonov², J F Noël², M Ostrick⁴, J Ottnad², B Otto², G Penman⁸, T Poller², D Proft⁶, G Reicherz¹², N Reinartz², L Richter², S Runkel^{2

6}, B Salisbury², A V Sarantsev², D Schaab², C Schmidt², H Schmieden⁶, J Schultes², T Seifen², K Spieker², N Stausberg², M Steinacher¹, F Taubert², A Thiel², U Thoma², A Thomas⁴, M Urban², G Urff², Y Usov⁵, H van Pee², Y C Wang², C Wendel², U Wiedner¹², Y Wunderlich²; CBELSA/TAPS Collaboration

Affiliations

¹ Department of Physics, University of Basel, Basel, Switzerland.
² Helmholtz-Institut für Strahlen-und Kernphysik, University of Bonn, Bonn, Germany.
³ II. Physikalisches Institut, University of Giessen, Giessen, Germany.
⁴ Institut für Kernphysik, University of Mainz, Mainz, Germany.
⁵ Joint Institute for Nuclear Research, Dubna, Russia.
⁶ Physikalisches Institut, University of Bonn, Bonn, Germany.
⁷ Department of Physics, Florida State University, Tallahassee, USA.
⁸ SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, UK.
⁹ Present Address: resent address: University of Liverpool, Liverpool, UK.
¹⁰ Present Address: resent address: University of Hamburg, Hamburg, Germany.
¹¹ Present Address: resent address: Ruhr University Bochum, Bochum, Germany.
¹² Institut für Experimentalphysik I, Ruhr University Bochum, Bochum, Germany.

Abstract

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 $γ p \to π^{0} p$ and $γ p \to η p$ 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.