The $5g-4f$ 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,$pm$,0.00018),MeV/c$^{2}$ ($pm$,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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