Measurement of the strong interaction width and shift of the ground state of pionic hydrogen.

G.C. Oades
Institute of Physics, Aarhus University, DK-8000 Aarhus, Denmark

S. Biri
Inst. of Nuclear Research (ATOMKI) of the Hungarian Academy of Sciences, H-4001, Debrecen

D. F. Anagnostopoulos
University of Ioannina, Greece

G. Borchert, D. Gotta
Institut für Kernphysik, Forschungsanlage Jülich, D-52425 Jülich, Germany

N. Nelms
Space Research Center, Department of Physics and Astronomy,University of Leicester, University Road, Leicester LE1 7RH, Great Britain

J.-P. Egger
Institut de Physique, Université de Neuchatel, Rue A.-L. Breguet CH-2000 Neuchatel

E. Bovet, G. Fiorucci
EISI, Rue Baptiste-Savoye 26 , CH-2610 St. Imier

P. Indelicato
Laboratoire Kastler-Brossel, Université Pierre et Marie Curie , 4 place Jussieu, F-75252 Paris Cedex 05, France

P. Hauser, P. A. Schmelzbach, L.M. Simons, V. E. Markushin
Paul Scherrer Institut, CH 5232 Villigen PSI, Switzerland

W. H. Breunlich, M. Cargnelli, B. Gartner, R. King, B. Lauss, J. Marton, H. Zmeskal
Institut für Mittelenergiephysik, Wien, Oesterreichische Akademie der Wissenschaften

F. Kottmann
Institut für Teilchenphysik, ETH Zürich, CH-8093 Zürich

G. Rasche
Institut für Theoretische Physik, Universität Zürich, CH-8057 Zürich

We propose to measure the strong interaction width and shift of the ground state of pionic hydrogen in order to determine the pion-nucleon scattering lengths for both isospin components and with a relative accuracy of better than . The scattering length extracted from the width measurement has a direct relation to the pion-nucleon coupling constant and can be directly compared with predictions of chiral perturbation theory. Systematic errors of the width measurement caused by Doppler broadening can be corrected by comparing simultaneous experiments with pionic and muonic hydrogen atoms.