We have measured the Balmer-series x-rays of kaonic $^4$He atoms using novel large-area silicon drift x-ray detectors in order to study the low-energy $bar{K}$-nucleus strong interaction. The energy of the $3d to 2p$ transition was determined to be 6467 $pm$ 3 (stat) $pm$ 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.
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