Determination of the 2p-1s transition energy and strong interaction shift in pionic hydrogen using crystal diffraction

The 2p-1s atomic transition in pionic hydrogen has been studied with the help of a point-focusing graphite diffraction spectrometer. The transition energy was measured to be E(2p-1s)=2433.5±1.7 eV. From this result a strong interaction shift of -3.9±1.7 eV was derived. The Kα x-ray yield in the 2.7 atm hydrogen target at 40 K was found to be 0.025±0.013 per stopped pion.