Strong interaction shift and width of the 1s level in pionic hydrogen.

The 3{ital p}{minus}1{ital s} x-ray line of pionic hydrogen was measured with a reflecting bent crystal spectrometer. The strong interaction energy level shift and the total decay width of the 1{ital s} state, obtained from the transition energy and the linewidth, are {var_epsilon}{sub 1{ital s}}={minus}7.127{plus_minus}0.028(stat){plus_minus}0.036(syst)eV (attractive) and {Gamma}{sub 1{ital s}}=0.97{plus_minus}0.10(stat){plus_minus}0.05(syst)eV. The corresponding hadronic {pi}{ital N} {ital s}-wave scattering lengths for elastic scattering and single charge exchange are {ital a}{sub {pi}{sup {minus}}{ital p}{r_arrow}{pi}{sup {minus}}{ital p}}{sup {ital h}}=0.0885{plus_minus}0.0009{ital m}{sub {pi}}{sup {minus}1} and {ital a}{sub {pi}{sup {minus}}{ital p}{r_arrow}{pi}{sup 0}{ital n}}{sup {ital h}}={minus}0.136{plus_minus}0.010{ital m}{sub {pi}}{sup {minus}1}. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.