Electron-Electron Interaction in Strong Electromagnetic Fields: The Two-Electron Contribution to the Ground-State Energy in He-like Uranium

Abstract

Radiative recombination transitions into the ground state of cooled bare and hydrogen-like uranium ions were measured at the storage ring ESR. By comparing the corresponding x-ray centroid energies, this technique allows for a direct measurement of the electron-electron contribution to the ionization potential in the heaviest He-like ions. For the two-electron contribution to the ionization potential of He-like uranium we obtain a value of 2248 ± 9 eV. This represents the most accurate determination of two-electron effects in the domain of high-Z He-like ions and the accuracy reaches already the size of the specific two-electron radiative QED corrections.

High-accuracy crystal spectroscopy of the n = 2 energy level of helium-like uranium

“…In the ground state of He-like uranium, these corrections are +8.0 eV, where the total two electron interaction is about −2245.9 eV and the one-electron QED corrections are −265.2 eV (one and two-loop corrections). These predictions were confirmed in a recent experiment [5] where the He-like uranium Lamb shift was measured with an accuracy of 9 eV. For the n = 2 levels, almost no experimental information is available in high-Z He-like ions (Z > 54).…”

“…Up to now, most of the measurements performed in this field were concentrated on the study of QED effects in hydrogen-like and lithium-like ions [1][2][3][4]. Recent progress in the spectroscopy of heavy ions [5] also opens new perspectives for studying higher order QED effects in heavy He-like ions, which are the simplest many-body systems. Investigations of these ions along the isoelectronic sequence up to the heaviest species probe uniquely our understanding of electron-electron correlation, relativistic, and quantum electrodynamics effects.…”

Precision studies of fundamental atomic structure with heaviest few-electron ions

“…It was also successfully applied at the EBIT facility in Heidelberg as well as in Tokyo [24]. We have applied this technique at the electron cooler of the ESR storage ring at GSI and extended the previous measurements to He-like uranium [25]. The achieved accuracy is just of the order required to access the two-electron α 2 -order self-energy.…”

“…The [22]. Full squares represent experimental values from EBITs [23,24] and the open square shows the result obtained for He-like uranium at the electron cooler of the ESR [25]. All results are in eV Nuclear Charge situation is very different in the high-Z regime, where practically no experimental data have been available up to now.…”

QED effects in heavy few-electron ions

“…[42] 280.59(10) Experiment [45] 280.52(10) [56] 2248(9) Table 4: The Bohr-Weisskopf correction ε, derived from experiments on muonic atoms [81], is compared with previous direct evaluations of this effect within the single-particle [77,78] and the many-particle [79,80] [78] 0.0118 0.0179 0.0179 Labzowsky et al [77] 0.0131 Tomaselli et al [79] 0.0210 Sen'kov and Dmitriev [80] 0.0095(+7, −38) …”