Kaonic Helium X-rays

Abstract

The long-standing "Kaonic-helium puzzle", i.e., the discrepancy between the measured and calculated 2p-level strong-interaction shift of kaonic helium 4, has been solved by the KEK E570 experiment; the measured 2p-level shift was 2 ± 2(stat) ± 2(syst) eV, thus agreeing with a majority of the theoretical calculations in contradiction to the previous average of 3 experiments of −43 ± 8eV. The smallness of the kaonic helium-4 2p-level shift has recently been confirmed by the SIDDHARTA collaboration at DAΦNE. Both of these experiments used silicon drift X-ray detectors (SDDs), and have used elaborate in-situ calibration methods. In order to further study the low-energy kaon-nucleus interaction, the J-PARC E17 experiment will soon measure the kaonic helium-3 2p-level shift to high precision. I also briefly discuss the status of kaonic hydrogen x-ray spectroscopy.