Strong-interaction shifts and widths of kaonic helium isotopes.

ABSTRACT

The kaonic 3He and 4He [Formula see text] transitions in gaseous targets were observed by the SIDDHARTA experiment. The X-ray energies of these transitions were measured with large-area silicon-drift detectors using the timing information of the [Formula see text] pairs produced by the DAΦNE [Formula see text] collider. The strong-interaction shifts and widths both of the kaonic 3He and 4He 2p states were determined, which are much smaller than the results obtained by the previous experiments. The "kaonic helium puzzle" (a discrepancy between theory and experiment) was now resolved.