Kaonic hydrogen X-ray measurement in SIDDHARTA
  Kaonic hydrogen atoms provide a unique laboratory to probe the kaon-nucleon strong interaction at the energy threshold, allowing an investigation of the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. The SIDDHARTA Collaboration has measured the $K$-series X rays of kaonic hydrogen atoms at the DA$\Phi$NE electron-positron collider of Laboratori Nazionali di Frascati, and has determined the most precise values of the strong-interaction induced shift and width of the $1s$ atomic energy level. This result provides vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction. 
M. Bazzi, G. Beer, L. Bombelli, A. M. Bragadireanu, M. Cargnelli, G.   Corradi, C. Curceanu (Petrascu), A. d'Uffizi, C. Fior...
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