DISCOVERY OF THE REPULSIVE ENERGY SHIFT OF THE KAONIC HYDROGEN 1S STATE

The aim in this manuscript is to clarify the progress in understanding the nature of the (K) over bar N interaction at the lowest energy, gi ven by the recent kaonic hydrogen X-ray experiment at KEK [1]. We have observed a clear spectrum showing the kaonic hydrogen K-alpha line, f or the first time. The analysis gives the repulsive energy shift to be Delta E(1s) = -323 +/- 63(statistical) +/- 11 (systematic) eV and the energy width to be Gamma(1s) = 407 +/- 208 +/- 100 eV. This result is consistent with analyses of the previous low-energy scattering data a nd resolves the long-standing kaonic hydrogen puzzle.