SOLVING THE KAONIC-HELIUM PUZZLE

We have measured the Balmer-series x-rays of kaonic He-4 atoms using large-area silicon drift x-ray detectors (SDDs) in order to study the low-energy (K) over bar -nucleus strong interaction. The energy of the 3d --> 2p transition was determined to be 6467 +/- 3(stat) +/- 2(syst) eV. The resulting strong-interaction energy-level shift is in agreement with theoretical calculations, thus eliminating a long-standing discrepancy between theory and experiment.