https://doi.org/10.1140/epja/i2014-14058-1
Regular Article - Experimental Physics
Determination of the 
mass with the Crystal Ball at MAMI-B
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
A new precise determination of the meson mass is presented. It is based on a measurement of the threshold for the 
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 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 
MeV agrees very well with the precise values of the NA48, KLOE, CLEO and COSY-ANKE Collaborations and deviates by 
from the smaller value obtained by the GEM Collaboration at COSY.
© SIF, Springer-Verlag Berlin Heidelberg, 2014
