Determination of the πN scattering lengths from pionic hydrogen

Abstract The final results from the pionic hydrogen X-ray experiment at PSI are presented. With this experiment the strong interaction energy level shift e 1s and the total decay width Γ 1s of the 1s state of pionic hydrogen were obtained from a precise measurement of the 3p–1s X-ray line: e 1s =−7.108±0.013(stat.)±0.034(syst.) eV (attractive) and Γ 1s = 0.868±0.040(stat.)±0.038(syst.) eV. The corresponding hadronic π N s-wave scattering lengths for elastic scattering and single charge exchange are: a π − p→π − p =0.0883±0.0008 m −1 π and a π − p→π 0 n =−0.128±0.006 m −1 π . Combining the results of the pionic hydrogen and deuterium measurements, the isoscalar ( b 0 ) and isovector ( b 1 ) scattering lengths, corresponding to an isospin symmetric interaction, can be calculated: b 0 =0.0016±0.0013 m −1 π and b 1 =−0.0868±0.0014 m −1 π .