Kaonic helium X-ray measurement in the SIDDHARTA experiment

The SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research with Timing Application) collaboration performed X-ray spectroscopy measurement of kaonic atoms at the DAΦNE e+e-collider. Low energy negative kaons from DAΦNE φ-factory were stopped in gaseous targets to produce kaonic atoms. We employed specially designed Silicon Drift Detectors(SDDs) to detect the kaonic X-rays. Based on the energy of kaonic- 4He 3d → 2p transition, we determined a new value of the 2p level strong-interaction shift of kaonic- 4He: 0 ± 6 (stat.)± 2 (syst.) eV. Together with the result of recent E570 experiment at the KEK-PS, a small shift (if any) of kaonic- 4He 2p level has become well established.