A new determination of the π−H and π−D 2P-1s strong interaction shifts using crystal diffraction

Abstract

The 2P-1S X-ray transition energy in pionic hydrogen (π − H) and pionic deuterium (π − D) has been measured using a curved graphite crystal spectrometer. E 2 P−1 S (π − H) = 2434.5 ± 0.4( stat) ± 0.3 (syst) eV , E 2 P−1 S (π − D) = 2592.1 ± 0.8 ( stat) ± 0.5 (syst) eV . The deduced strong interaction shifts ΔE(π − H) = −4.9 ± 0.4 ( stat) ± 0.3 (syst) eV , ΔE(π − D) = +5.5 ± 0.8 ( stat) ± 0.5 (syst) eV , corresponding to the S-wave scattering lengths Rea π− p 0 = +0.084 ±0.009 fm , Rea π− d 0 = −0.083 ± 0.014 fm , are compared with recent calculations. The X-ray yield is found to be 0.04 ± 0.02 2P-1S X-rays per stopped π − in saturated hydrogen vapour of 3 atm pressure.