Determination of the mass with the Crystal Ball at MAMI-B

A. Nikolaev; P. Aguar-Bartolomé; J. Ahrens; J. R. M. Annand; H. J. Arends; R. Beck; V. Bekrenev; B. Boillat; A. Braghieri; D. Branford; W. J. Briscoe; J. W. Brudvik; S. Cherepnya; R. Codling; M. Dehn; E. J. Downie; L. V. Fil’kov; D. I. Glazier; R. Gregor; E. Heid; D. Hornidge; O. Jahn; A. Jankowiak; K. -H. Kaiser; V. L. Kashevarov; R. Kondratiev; M. Korolija; M. Kotulla; D. Krambrich; B. Krusche; M. Lang; V. Lisin; K. Livingston; U. Ludwig-Mertin; S. Lugert; I. J. D. MacGregor; D. M. Manley; M. Martinez-Fabregate; J. C. McGeorge; D. Mekterovic; V. Metag; B. M. K. Nefkens; R. Novotny; R. O. Owens; P. Pedroni; A. Polonski; S. N. Prakhov; J. W. Price; A. Reiter; G. Rosner; M. Rost; T. Rostomyan; S. Schumann; D. Sober; A. Starostin; I. Supek; C. M. Tarbert; A. Thomas; M. Unverzagt; Th. Walcher; D. P. Watts; F. Zehr

doi:10.1140/epja/i2014-14058-1

2024 Impact factor 2.8

Hadrons and Nuclei

Eur. Phys. J. A (2014) 50: 58
https://doi.org/10.1140/epja/i2014-14058-1

Regular Article - Experimental Physics

Determination of the $\eta$ mass with the Crystal Ball at MAMI-B

The Crystal Ball at MAMI, TAPS and A2 Collaborations
A. Nikolaev¹, P. Aguar-Bartolomé², J. Ahrens², J. R. M. Annand³, H. J. Arends², R. Beck¹^*, V. Bekrenev⁴, B. Boillat⁵, A. Braghieri⁶, D. Branford⁷, W. J. Briscoe⁸, J. W. Brudvik⁹, S. Cherepnya¹⁰, R. Codling³, M. Dehn², E. J. Downie³, L. V. Fil’kov¹⁰, D. I. Glazier⁷, R. Gregor¹¹, E. Heid², D. Hornidge¹², O. Jahn², A. Jankowiak², K. -H. Kaiser², V. L. Kashevarov²^,10, R. Kondratiev¹³, M. Korolija¹⁴, M. Kotulla¹¹, D. Krambrich², B. Krusche⁵, M. Lang¹, V. Lisin¹³, K. Livingston³, U. Ludwig-Mertin², S. Lugert¹¹, I. J. D. MacGregor³, D. M. Manley¹⁵, M. Martinez-Fabregate², J. C. McGeorge³, D. Mekterovic¹⁴, V. Metag¹¹, B. M. K. Nefkens⁹, R. Novotny¹¹, R. O. Owens³, P. Pedroni⁶, A. Polonski¹³, S. N. Prakhov⁹, J. W. Price⁹, A. Reiter²^,3, G. Rosner³, M. Rost², T. Rostomyan⁵^,6, S. Schumann¹^,2, D. Sober¹⁶, A. Starostin⁹, I. Supek¹⁴, C. M. Tarbert⁷, A. Thomas², M. Unverzagt¹^,2, Th. Walcher², D. P. Watts⁷ and F. Zehr⁵

¹ Helmholtz-Institut für Strahlen- und Kernphysik, University Bonn, Bonn, Germany
² Institut für Kernphysik, University Mainz, Mainz, Germany
³ Department of Physics and Astronomy, University of Glasgow, Glasgow, UK
⁴ Petersburg Nuclear Physics Institute, Gatchina, Russia
⁵ Institut für Physik, University Basel, Basel, Switzerland
⁶ INFN, Sezione di Pavia, Pavia, Italy
⁷ School of Physics, University of Edinburgh, Edinburgh, UK
⁸ Center for Nuclear Studies, The George Washington University, Washington, USA
⁹ University of California Los Angeles, Los Angeles, California, USA
¹⁰ Lebedev Physical Institute, Moscow, Russia
¹¹ II. Physikalisches Institut, University Gießen, Gießen, Germany
¹² Mount Allison University, Sackville, Canada
¹³ Institute for Nuclear Research, Moscow, Russia
¹⁴ Rudjer Boskovic Institute, Zagreb, Croatia
¹⁵ Kent State University, Kent, Ohio, USA
¹⁶ The Catholic University of America, Washington, USA

^* e-mail: beck@hiskp.uni-bonn.de

Received: 4 July 2013
Revised: 6 February 2014
Accepted: 20 February 2014
Published online: 24 March 2014

Abstract

A new precise determination of the $\eta$ meson mass is presented. It is based on a measurement of the threshold for the $\gamma p\rightarrow p\eta$ reaction using the tagger focal-plane microscope detector at the MAMI-B facility in Mainz. The tagger microscope has a higher energy resolution than the standard tagging spectrometer and, hence, allowed an improvement in the accuracy compared to the previous $\eta$ mass measurement at MAMI-B. Special emphasis was put on a very careful energy calibration of the electron beam and the tagging device, which reduced considerably the systematic uncertainty compared to the previous MAMI experiment. The result $m_{\eta}=(547.865 \pm 0.031_{stat.}\pm 0.062_{syst.})$ MeV agrees very well with the precise values of the NA48, KLOE, CLEO and COSY-ANKE Collaborations and deviates by $6\sigma$ from the smaller value obtained by the GEM Collaboration at COSY.