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The 5g − 4 f transitions in pionic nitrogen and muonic oxygen were measured simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4 bar. Due to the precise knowledge of the muon mass the muonic line provides the energy calibration for the pionic transition. A value of (139.57077 ± 0.00018) MeV/c 2 (± 1.3ppm) is derived for the mass of the negatively charged pion, which is 4.2ppm larger than the present world average.

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