Precision spectroscopy of Kaonic Helium 3d → 2p X-rays

We have measured the strong-interaction shift of 2 p states of kaonic helium-4 atoms with a precision of ∼2 eV using Silicon Drift Detectors (SDDs) which lead to much improved energy resolution and signal-to-noise ratio compared to the conventional Si(Li) x-ray detector used in the past experiments. The measurement will give an answer to the longstanding “kaonic helium puzzle” and provide crucial information to understand the basis of the Akaishi-Yamazaki prediction of deeply-bound kaonic nuclei, which is one of the interpretations of the strange multibaryon candidates recently reported at KEK, DAΦNE and BNL.