STRONG INTERACTION SHIFT AND WIDTH OF THE 1S LEVEL IN PIONIC HYDROGEN

The 3p-1s 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 Is state, obtained from the transitio n energy and the linewidth, are epsilon(1s) = -7.127 +/- 0.028(stat) /- 0.036(syst) eV (attractive) and Gamma(1s) = 0.97 +/- 0.10(stat) +/- 0.05(syst) eV. The corresponding hadronic pi N s-wave scattering leng ths for elastic scattering and single charge exchange are a(pi)(h)-(p- ->pi)-(p) = 0.0885 +/- 0.0009m(pi)(-1) and a(pi)-(h)(p-->pi)0(n) = -0. 136 +/- 0.010m(pi)(-1).