,
S. Biri
,
G. Borchert
,
W. H. Breunlich
,
M. Cargnelli,
J.-P. Egger
,
B. Gartner,
D. Gotta,
P. Hauser
,
M. Hennebach,
P. Indelicato
,
T. Jensen,
R. King,
F. Kottmann
,
B. Lauss,
Y. W. Liu,
V. E. Markushin,
J. Marton,
N. Nelms
,
G. C. Oades
,
G. Rasche
,
P. A. Schmelzbach,
L. M. Simons,
J. Zmeskal
Department of Material Science, University of Ioannina,
GR-45110 Ioannina, Greece
Institute of Nuclear Research (ATOMKI) of the Hungarian
Academy of Sciences, H-4001,Debrecen, Hungary
Institut für Kernphysik, Forschungszentrum Jülich,
D-52425 Jülich, Germany
Institut für Mittelenergiephysik,A-1090 Wien,
Österreichische Akademie der Wissenschaften, Austria
Institut de Physique de l'Université de Neuchâtel,
CH-2000 Neuchâtel, Switzerland
Paul-Scherrer-Institut (PSI), CH-5232 Villigen, Switzerland
Laboratoire Kastler-Brossel, Université Pierre et Marie Curie,
F-75252 Paris, France
Institut für Teilchenphysik, ETH Zürich, CH-8057
Zürich , Switzerland
Department of Astronomy and Physics, University of Leicester,
Leicester LEI7RH, England
Institute of Physics, Aarhus University, DK-8000 Aarhus, Denmark
Institut für Theoretische Physik, Universität
Zürich, Switzerland
a stringent
test of chiral perturbation theory and a determination
of the pion nucleon coupling constant can be obtained.
Past measurements determined
the shift with an accuracy better than , and the width with an
accuracy of 
. Additional information from pionic deuterium
measurements has been used in order to extract isospin separated scattering
lengths with sufficient accuracy.
Future measurements plan to directly measure the width of
pionic hydrogen with an accuracy on the level on .