Hadronic shift in pionic hydrogen

The hadronic shift in pionic hydrogen has been redetermined to be ${ϵ}_{1s}=7.086\pm 0.007(stat)\pm 0.006(sys)$,eV by X-ray spectroscopy of ground state transitions applying various energy calibration schemes. The experiment was performed at the high-intensity low-energy pion beam of the Paul Scherrer Institut by using the cyclotron trap and an ultimate-resolution Bragg spectrometer with bent crystals.