Balmer α transitions in antiprotonic hydrogen and deuterium

The strong-interaction shifts ε and broadenings Γ of the 2p levels in antiprotonic hydrogen and deuterium have been measured for the first time with a crystal spectrometer. In hydrogen, the 23P0 hyperfine state could be resolved from the three close-lying states 23P2, 21P1, and 23P1. The hadronic shift was determined to be ε23P0=+139±28 meV (attractive). The value found for Γ23P0=120±25 meV is much larger than the spin-averaged 2p-level broadening Γbarbal2p as determined from earlier experiments measuring the intensity balance. The average shift of the three unresolved states is consistent with zero and a mean broadening of Γbar2(3P2,1P1,3P1)=38±9 meV was measured. In deuterium, the spin-averaged hadronic shift and broadening were found to be εbar2p=-243±26 meV (repulsive) and Γbar2p=489±30 meV