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We propose to measure the strong interaction width and shift of the ground of pionic hydrogen in order to determine the pion-nucleon scattering lengths for both isospin components a+ and aˉ with a relative accuracy of better than 10ˉ˛. The scattering length aˉ 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. The present experiment serve to test the Quantum chromodynamic QCD at low energies. For more description of the experiments see:at Paul Scherrer Institute PSI










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