Photoproduction of pairs off nucleons and deuterons

A. Käser; F. Müller; J. Ahrens; J. R. M. Annand; H. J. Arends; K. Bantawa; P. A. Bartolome; R. Beck; A. Braghieri; W. J. Briscoe; S. Cherepnya; S. Costanza; M. Dieterle; E. J. Downie; P. Drexler; L. V. Fil’kov; A. Fix; S. Garni; D. I. Glazier; D. Hamilton; D. Hornidge; D. Howdle; G. M. Huber; I. Jaegle; T. C. Jude; V. L. Kashevarov; I. Keshelashvili; R. Kondratiev; M. Korolija; B. Krusche; V. Lisin; K. Livingston; I. J. D. MacGregor; Y. Maghrbi; J. Mancell; D. M. Manley; Z. Marinides; J. C. McGeorge; E. McNicoll; D. Mekterovic; V. Metag; S. Micanovic; D. G. Middleton; A. Mushkarenkov; A. Nikolaev; R. Novotny; M. Oberle; M. Ostrick; P. Otte; B. Oussena; P. Pedroni; F. Pheron; A. Polonski; S. Prakhov; J. Robinson; T. Rostomyan; S. Schumann; M. H. Sikora; D. Sober; A. Starostin; Th. Strub; I. Supek; M. Thiel; A. Thomas; M. Unverzagt; N. K. Walford; D. P. Watts; D. Werthmüller; L. Witthauer

doi:10.1140/epja/i2016-16272-1

2023 Impact factor 2.6

Hadrons and Nuclei

Eur. Phys. J. A (2016) 52: 272
https://doi.org/10.1140/epja/i2016-16272-1

Regular Article - Experimental Physics

Photoproduction of $\eta$ $\pi$ pairs off nucleons and deuterons

The A2 Collaboration
A. Käser¹, F. Müller¹, J. Ahrens², J. R. M. Annand³, H. J. Arends², K. Bantawa⁴, P. A. Bartolome², R. Beck²^,5, A. Braghieri⁶, W. J. Briscoe⁷, S. Cherepnya⁸, S. Costanza⁶, M. Dieterle¹, E. J. Downie²^,3^,7, P. Drexler⁹, L. V. Fil’kov⁸, A. Fix¹⁰, S. Garni¹, D. I. Glazier³^,11, D. Hamilton³, D. Hornidge¹², D. Howdle³, G. M. Huber¹³, I. Jaegle¹, T. C. Jude¹¹, V. L. Kashevarov²^,8, I. Keshelashvili¹, R. Kondratiev¹⁴, M. Korolija¹⁵, B. Krusche¹^*, V. Lisin¹⁴, K. Livingston³, I. J. D. MacGregor³, Y. Maghrbi¹, J. Mancell³, D. M. Manley⁴, Z. Marinides⁷, J. C. McGeorge³, E. McNicoll³, D. Mekterovic¹⁵, V. Metag⁹, S. Micanovic¹⁵, D. G. Middleton¹², A. Mushkarenkov⁶, A. Nikolaev²^,5, R. Novotny⁹, M. Oberle¹, M. Ostrick², P. Otte², B. Oussena²^,7, P. Pedroni⁶, F. Pheron¹, A. Polonski¹⁴, S. Prakhov¹⁶, J. Robinson³, T. Rostomyan¹, S. Schumann²^,5, M. H. Sikora¹¹, D. Sober¹⁷, A. Starostin¹⁶, Th. Strub¹, I. Supek¹⁵, M. Thiel⁹, A. Thomas², M. Unverzagt²^,5, N. K. Walford¹, D. P. Watts¹¹, D. Werthmüller¹^,3 and L. Witthauer¹

¹ Department of Physics, University of Basel, CH-4056, Basel, Switzerland
² Institut für Kernphysik, University of Mainz, D-55099, Mainz, Germany
³ SUPA School of Physics and Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK
⁴ Kent State University, 44242, Kent, OH, USA
⁵ Helmholtz-Institut für Strahlen- und Kernphysik, University Bonn, D-53115, Bonn, Germany
⁶ INFN Sezione di Pavia, I-27100 Pavia, Pavia, Italy
⁷ Center for Nuclear Studies, The George Washington University, 20052, Washington, USA
⁸ Lebedev Physical Institute, RU-119991, Moscow, Russia
⁹ II. Physikalisches Institut, University of Giessen, D-35392, Giessen, Germany
¹⁰ Laboratory of Mathematical Physics, Tomsk Polytechnic University, Tomsk, Russia
¹¹ SUPA School of Physics, University of Edinburgh, EH9 3JZ, Edinburgh, UK
¹² Mount Allison University, E4L3B5, Sackville, New Brunswick, Canada
¹³ University of Regina, SK S4S-0A2, Regina, Canada
¹⁴ Institute for Nuclear Research, RU-125047, Moscow, Russia
¹⁵ Rudjer Boskovic Institute, HR-10000, Zagreb, Croatia
¹⁶ University of California Los Angeles, 90095-1547, Los Angeles, California, USA
¹⁷ The Catholic University of America, 20064, Washington, USA

^* e-mail: Bernd.Krusche@unibas.ch

Received: 4 April 2016
Accepted: 12 July 2016
Published online: 9 September 2016

Abstract

Quasi-free photoproduction of $\pi\eta$ -pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^{0}\eta$ , $\gamma n\rightarrow n\pi^{0}\eta$ , $\gamma p\rightarrow n\pi^{+}\eta$ , and $\gamma n\rightarrow p\pi^{-}\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial-state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $\pi^{0}\eta$ pairs from nucleons bound in ³ He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost 4 $\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential $\Delta^{\star}3/2^{-}\rightarrow \eta\Delta(1232) \rightarrow\pi\eta N$ decay chain, mainly with $\Delta(1700)3/2^{-}$ and $\Delta(1940)3/2^{-}$ . The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.