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Abstract. The hadronic shift in pionic hydrogen has been redetermined to be 1s = 7.086 ± 0.007(stat) ± 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.

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The x rays of the pionic deuterium 2p-1s transition were measured with a high resolution crystal spectrometer including a cyclotron trap ͑a magnetic device to increase the pion stopping density͒ and a CCD ͑chargecoupled device͒ detector system. The 1s strong interaction shift ⑀ 1s and total width ⌫ 1s were determined from the position and line shape of the x-ray peak. The ͑complex͒ pionic deuterium s-wave scattering length a Ϫ d was deduced. Its real part was related to the pion-nucleon scattering lengths, and the isoscalar coupling constant for Ϫ absorption was deduced from the imaginary part. ͓S0556-2813͑98͒50310-X͔ PACS number͑s͒: 25.80.Hp, 36.10.Gv