Observation of kaonic hydrogen atom x rays

We have measured the K-series x rays from kaonic hydrogen atoms and have succeeded for the first time in observing a distinct [Formula Presented] peak. The L x-ray peak has also been observed. The strong-interaction shift and width of the kaonic hydrogen atom [Formula Presented] state were determined from the transition energy and the line width of the [Formula Presented] x rays. The sign of the strong-interaction shift was confirmed to be repulsive, with the results [Formula Presented] and [Formula Presented] The measured shift and width of the [Formula Presented] state are consistent with those expected from other low energy [Formula Presented] data, and thus the long-standing kaonic hydrogen puzzle is resolved. The [Formula Presented] x-ray yield per stopped kaon was estimated to be [Formula Presented] at a hydrogen target density of [Formula Presented].