Adjustment of the Crystal-Diffraction Measurement of the Pion Mass

Abstract

The measurement of the negative-pion mass by crystal diffraction of pionic x rays is adjusted for the revised fine-structure constant, improved radiative energy-level calculations, and more precise values of the calibration lines. We find that the result quoted earlier should be reduced by 80 ppm (parts per million) to 139.566±0.010 MeV (± 73 ppm).