Observation of Kaonic Hydrogen<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mi>α</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>X Rays

We have measured the shift and width of the kaonic hydrogen $1s$ state due to the $\overline{K}N$ strong interaction. We have observed, for the first time, distinct $K$-series kaonic hydrogen x rays with good signal-to-noise ratio in the energy spectrum. The measured energy shift and width were determined to be $\ensuremath{\Delta}E(1s)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}323\ifmmode\pm\else\textpm\fi{}63(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}11(\mathrm{syst})\mathrm{eV}$ (repulsive) and $\ensuremath{\gamma}(1s)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}407\ifmmode\pm\else\textpm\fi{}208(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}100(\mathrm{syst})\mathrm{eV}$, respectively.