Measurements of strong-interaction effects in kaonic-helium isotopes at sub-eV precision with X-ray microcalorimeters

Hashimoto, Tadashi   ; Tanida, Kiyoshi   ; 68 of others*

We have measured the transition X-rays of kaonic He and He atoms using superconducting transition-edge-sensor microcalorimeters with an energy resolution better than 6 eV (FWHM). We determined the energies to be (stat) (syst) eV and (stat) (syst) eV, and widths to be (stat) (syst) eV and (stat) (stat) eV, for kaonic He and He, respectively. These values are nearly 10 times more precise than in previous measurements. Our results exclude the large strong-interaction shifts and widths that are suggested by a coupled-channel approach, and agree with calculations based on optical-potential models.