title: Testing QED screening and two-loop contributions with He-Like ions.
abstract: We report wavelength measurements of H-like and He-like ions obtained with a novel x-ray spectrometer at the Heidelberg Electron Beam Ion Trap. The experimental uncertainty for the Lyman-alpha1 wavelength in Cl16+ is reduced by a factor of 3 and, as expected, excellent agreement with theory is maintained. For the resonance line in He-like Ar16+, an uncertainty of only deltalambda/lambda=2x10(-6) was achieved. This is the most precise x-ray wavelength reported for highly charged ions to date, and allows to test recent predictions on QED two-electron and two-photon radiative corrections for He-like ions. The results also point to the advantages of establishing absolute x-ray wavelength standards using Lyman-alpha transitions (in the present case Ar17+ Lyman-alpha1) to supersede the current ones.
authors.affiliation: Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany. hbruhns@astro.columbia.edu
authors.forename: H
authors.initials: H
authors.lastname: Bruhns
authors.forename: J
authors.initials: J
authors.lastname: Braun
authors.forename: K
authors.initials: K
authors.lastname: Kubicek
authors.forename: J R
authors.initials: JR
authors.lastname: Crespo López-Urrutia
authors.forename: J
authors.initials: J
authors.lastname: Ullrich