X-ray transitions in pionic nitrogen were measured using a curved crystal spectrometer. From the transition energy, calibrated with the help of the copper Ka1,2 electronic transition, a value for the charged pion mass of (139.57071± 0.00053) MeV/c2 was deduced. In order to reduce the uncertainty of the charged pion mass in the level of 1 ppm, we propose the determination of pionic transition energy based on the more precisely known energies and line shapes of muonic transitions.
X‐Ray Spectroscopic Observations of EX Hydrae and Mass Determination of the White Dwarf