Precision X-ray spectroscopy of kaonic atoms as a probe of low-energy   kaon-nucleus interaction
  In the exotic atoms where one atomic $1s$ electron is replaced by a $K^{-}$, the strong interaction between the $K^{-}$ and the nucleus introduces an energy shift and broadening of the low-lying kaonic atomic levels which are determined by only the electromagnetic interaction. By performing X-ray spectroscopy for Z=1,2 kaonic atoms, the SIDDHARTA experiment determined with high precision the shift and width for the $1s$ state of $K^{-}p$ and the $2p$ state of kaonic helium-3 and kaonic helium-4. These results provided unique information of the kaon-nucleus interaction in the low energy limit. 
H. Shi, M. Bazzi, G. Beer, G. Bellotti, C. Berucci, A. M.   Bragadireanu, D. Bosnar, M. Cargnelli, C. Curceanu, A. D. Butt, ...
nucl-ex