Precision Spectroscopy of Pionic Atoms: From Pion Mass Evaluation to Tests of Chiral Perturbation Theory

Preliminary results of the strong interaction shift and width in pionic hydrogen ($\pi H$) using an X-ray spectrometer with spherically bent crystals and CCDs as X-ray detector are presented. In the experiment at the Paul Scherrer Institute three different $(np\to 1s)$ transitions in $\pi H$ were measured. Moreover the pion mass measurement using the $(5 \to 4)$ transitions in pionic nitrogen and muonic oxygen is presented