Narrow structure in the excitation function of η photoproduction off the neutron

D Werthmüller; L Witthauer; I Keshelashvili; P Aguar-Bartolomé; J Ahrens; J R M Annand; H J Arends; K Bantawa; R Beck; V Bekrenev; A Braghieri; D Branford; W J Briscoe; J Brudvik; S Cherepnya; B Demissie; M Dieterle; E J Downie; P Drexler; L V Fil'kov; A Fix; D I Glazier; D Hamilton; E Heid; D Hornidge; D Howdle; G M Huber; I Jaegle; O Jahn; T C Jude; A Käser; V L Kashevarov; R Kondratiev; M Korolija; S P Kruglov; B Krusche; A Kulbardis; V Lisin; K Livingston; I J D MacGregor; Y Maghrbi; J Mancell; D M Manley; Z Marinides; M Martinez; J C McGeorge; E F McNicoll; V Metag; D G Middleton; A Mushkarenkov; B M K Nefkens; A Nikolaev; R Novotny; M Oberle; M Ostrick; B Oussena; P Pedroni; F Pheron; A Polonski; S N Prakhov; J Robinson; G Rosner; T Rostomyan; S Schumann; M H Sikora; D Sober; A Starostin; I Supek; M Thiel; A Thomas; M Unverzagt; D P Watts; Crystal Ball/TAPS experiment at MAMI, A2 Collaboration

doi:10.1103/PhysRevLett.111.232001

Narrow structure in the excitation function of η photoproduction off the neutron

Phys Rev Lett. 2013 Dec 6;111(23):232001. doi: 10.1103/PhysRevLett.111.232001. Epub 2013 Dec 4.

Authors

D Werthmüller¹, L Witthauer¹, I Keshelashvili¹, P Aguar-Bartolomé², J Ahrens², J R M Annand³, H J Arends², K Bantawa⁴, R Beck⁵, V Bekrenev⁶, A Braghieri⁷, D Branford⁸, W J Briscoe⁹, J Brudvik¹⁰, S Cherepnya¹¹, B Demissie⁹, M Dieterle¹, E J Downie¹², P Drexler¹³, L V Fil'kov¹¹, A Fix¹⁴, D I Glazier⁸, D Hamilton³, E Heid², D Hornidge¹⁵, D Howdle³, G M Huber¹⁶, I Jaegle¹, O Jahn², T C Jude⁸, A Käser¹, V L Kashevarov¹⁷, R Kondratiev¹⁸, M Korolija¹⁹, S P Kruglov⁶, B Krusche¹, A Kulbardis⁶, V Lisin¹⁸, K Livingston³, I J D MacGregor³, Y Maghrbi¹, J Mancell³, D M Manley⁴, Z Marinides⁹, M Martinez², J C McGeorge³, E F McNicoll³, V Metag¹³, D G Middleton¹⁵, A Mushkarenkov⁷, B M K Nefkens¹⁰, A Nikolaev⁵, R Novotny¹³, M Oberle¹, M Ostrick², B Oussena²⁰, P Pedroni⁷, F Pheron¹, A Polonski¹⁸, S N Prakhov²¹, J Robinson³, G Rosner³, T Rostomyan¹, S Schumann⁵, M H Sikora⁸, D Sober²², A Starostin¹⁰, I Supek¹⁹, M Thiel²³, A Thomas², M Unverzagt⁵, D P Watts⁸; Crystal Ball/TAPS experiment at MAMI, A2 Collaboration

Affiliations

¹ Departement für Physik, Universität Basel, Switzerland.
² Institut für Kernphysik, Universität Mainz, Germany.
³ SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
⁴ Kent State University, Kent, Ohio, USA.
⁵ Institut für Kernphysik, Universität Mainz, Germany and Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Germany.
⁶ Petersburg Nuclear Physics Institute, Gatchina, Russia.
⁷ INFN Sezione di Pavia, Pavia, Italy.
⁸ SUPA, School of Physics, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom.
⁹ Institute for Nuclear Studies, The George Washington University, Washington, District of Columbia, USA.
¹⁰ University of California at Los Angeles, Los Angeles, California, USA.
¹¹ Lebedev Physical Institute, Moscow, Russia.
¹² Institut für Kernphysik, Universität Mainz, Germany and SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom and Institute for Nuclear Studies, The George Washington University, Washington, District of Columbia, USA.
¹³ II. Physikalisches Institut, Universität Giessen, Germany.
¹⁴ Laboratory of Mathematical Physics, Tomsk Polytechnic University, Tomsk, Russia.
¹⁵ Mount Allison University, Sackville, New Brunswick E4L 1E6, Canada.
¹⁶ University of Regina, Regina, SK S4S 0A2, Canada.
¹⁷ Institut für Kernphysik, Universität Mainz, Germany and Lebedev Physical Institute, Moscow, Russia.
¹⁸ Institute for Nuclear Research, Moscow, Russia.
¹⁹ Rudjer Boskovic Institute, Zagreb, Croatia.
²⁰ Institut für Kernphysik, Universität Mainz, Germany and Institute for Nuclear Studies, The George Washington University, Washington, District of Columbia, USA.
²¹ Institut für Kernphysik, Universität Mainz, Germany and Institute for Nuclear Studies, The George Washington University, Washington, District of Columbia, USA and University of California at Los Angeles, Los Angeles, California, USA.
²² The Catholic University of America, Washington, District of Columbia, USA.
²³ Institut für Kernphysik, Universität Mainz, Germany and II. Physikalisches Institut, Universität Giessen, Germany.

PMID: 24476257
DOI: 10.1103/PhysRevLett.111.232001

Abstract

The photoproduction of η mesons off nucleons bound in 2H and 3He has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the η→2γ and η→3π0 decays and the recoil nucleons were detected with an almost 4π electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of γn→nη. The results from the two measurements are consistent, taking into account the expected effects from nuclear Fermi motion. The best estimates for position and intrinsic width of the structure are W=(1670±5) MeV and Γ=(30±15) MeV. For the first time precise results for the angular dependence of this structure have been extracted.