Coherent photoproduction of π0- and η-mesons off 7Li

Y. Maghrbi; B. Krusche; J. Ahrens; J. R. M. Annand; H. J. Arends; R. Beck; V. Bekrenev; B. Boillat; A. Braghieri; D. Branford; W. J. Briscoe; J. Brudvik; S. Cherepnya; R. F. B. Codling; E. J. Downie; P. Drexler; L. V. Fil’kov; A. Fix; D. I. Glazier; R. Gregor; E. Heid; D. Hornidge; I. Jaegle; O. Jahn; V. L. Kashevarov; I. Keshelashvili; A. Knezevic; R. Kondratiev; M. Korolija; D. Krambrich; M. Lang; V. Lisin; K. Livingston; S. Lugert; I. J. D. MacGregor; D. M. Manley; M. Martinez; J. C. McGeorge; D. Mekterovic; V. Metag; B. M. K. Nefkens; A. Nikolaev; R. Novotny; M. Ostrick; P. Pedroni; F. Pheron; A. Polonski; S. Prakhov; J. W. Price; G. Rosner; M. Rost; T. Rostomyan; S. Schadmand; S. Schumann; D. Sober; A. Starostin; I. Supek; C. M. Tarbert; A. Thomas; M. Unverzagt; D. P. Watts; D. Werthmüller; F. Zehr

doi:10.1140/epja/i2013-13038-3

2022 Impact factor 2.7

Hadrons and Nuclei

Eur. Phys. J. A (2013) 49: 38
https://doi.org/10.1140/epja/i2013-13038-3

Regular Article - Experimental Physics

Coherent photoproduction of π⁰- and η-mesons off ⁷Li

The Crystal Ball at MAMI, TAPS, and A2 Collaborations
Y. Maghrbi¹³⁸, B. Krusche¹³⁸^*, J. Ahrens²³⁸, J. R. M. Annand³³⁸, H. J. Arends²³⁸, R. Beck²³⁸^,438, V. Bekrenev⁵³⁸, B. Boillat¹³⁸, A. Braghieri⁶³⁸, D. Branford⁷³⁸, W. J. Briscoe⁸³⁸, J. Brudvik⁹³⁸, S. Cherepnya¹⁰³⁸, R. F. B. Codling³³⁸, E. J. Downie²³⁸^,338^,838, P. Drexler¹¹³⁸, L. V. Fil’kov¹⁰³⁸, A. Fix¹²³⁸, D. I. Glazier⁷³⁸, R. Gregor¹¹³⁸, E. Heid²³⁸, D. Hornidge¹³³⁸, I. Jaegle¹³⁸, O. Jahn²³⁸, V. L. Kashevarov¹⁰³⁸^,238, I. Keshelashvili¹³⁸, A. Knezevic¹⁴³⁸, R. Kondratiev¹⁵³⁸, M. Korolija¹⁴³⁸, D. Krambrich²³⁸, M. Lang²³⁸^,438, V. Lisin¹⁵³⁸, K. Livingston³³⁸, S. Lugert¹¹³⁸, I. J. D. MacGregor³³⁸, D. M. Manley¹⁶³⁸, M. Martinez²³⁸, J. C. McGeorge³³⁸, D. Mekterovic¹⁴³⁸, V. Metag¹¹³⁸, B. M. K. Nefkens⁹³⁸, A. Nikolaev²³⁸^,438, R. Novotny¹¹³⁸, M. Ostrick²³⁸, P. Pedroni⁶³⁸, F. Pheron¹³⁸, A. Polonski¹⁵³⁸, S. Prakhov⁹³⁸, J. W. Price⁹³⁸, G. Rosner³³⁸, M. Rost²³⁸, T. Rostomyan⁶³⁸, S. Schadmand¹¹³⁸, S. Schumann²³⁸^,438, D. Sober¹⁷³⁸, A. Starostin⁹³⁸, I. Supek¹⁴³⁸, C. M. Tarbert⁷³⁸, A. Thomas²³⁸, M. Unverzagt²³⁸^,438, D. P. Watts⁷³⁸, D. Werthmüller¹³⁸ and F. Zehr¹³⁸

¹³⁸ Department of Physics, University of Basel, Ch-4056, Basel, Switzerland
²³⁸ Institut für Kernphysik, University of Mainz, D-55099, Mainz, Germany
³³⁸ School of Physics and Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK
⁴³⁸ Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, D-53115, Bonn, Germany
⁵³⁸ Petersburg Nuclear Physics Institute, RU-188300, Gatchina, Russia
⁶³⁸ INFN, Sezione di Pavia, I-27100, Pavia, Italy
⁷³⁸ School of Physics, University of Edinburgh, EH9 3JZ, Edinburgh, UK
⁸³⁸ Center for Nuclear Studies, The George Washington University, 20052, Washington, DC, USA
⁹³⁸ University of California Los Angeles, 90095-1547, Los Angeles, California, USA
¹⁰³⁸ Lebedev Physical Institute, RU-119991, Moscow, Russia
¹¹³⁸ II. Physikalisches Institut, University of Giessen, D-35392, Giessen, Germany
¹²³⁸ Laboratory of Mathematical Physics, Tomsk Polytechnic University, Tomsk, Russia
¹³³⁸ Mount Allison University, New Brunswick, E4L3B5, Sackville, Canada
¹⁴³⁸ Rudjer Boskovic Institute, HR-10000, Zagreb, Croatia
¹⁵³⁸ Institute for Nuclear Research, RU-125047, Moscow, Russia
¹⁶³⁸ Kent State University, 44242, Kent, Ohio, USA
¹⁷³⁸ The Catholic University of America, 20064, Washington, DC, USA

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

Received: 18 January 2013
Revised: 14 February 2013
Accepted: 5 March 2013
Published online: 21 March 2013

Abstract

Coherent photoproduction of π⁰-mesons from threshold (E _th ≈ 136 MeV) throughout the Δ-resonance region and of η-mesons close to the production threshold (E _th ≈ 570 MeV for η has been measured for ⁷Li nuclei. The experiment was performed using the tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4π solid-angle electromagnetic calorimeter. The reactions were identified by a combined invariant-mass and missing-energy analysis. A comparison of the pion data to plane-wave impulse modelling tests the nuclear mass form factor. So far coherent η production had been only identified for the lightest nuclear systems (²H and ³He . For ³He a large enhancement of the cross section above plane-wave approximations had been reported, indicating the formation of a quasi-bound state. The present Li data for η production agree with a plane-wave approximation. Contrary to ³He , neither a threshold enhancement of the total cross section nor a deviation of the angular distributions from the expected form factor dependence were observed.