Proof-of-principle experiment for testing strong-field quantum electrodynamics with exotic atoms; High precision X-ray spectroscopy of muonic neon

Okumura, Takuma*; Hashimoto, Tadashi   ; 40 of others*

To test bound-state quantum electrodynamics (BSQED) in the strong-field regime, we have performed high-precision X-ray spectroscopy of the 5-4 and 5-4 transitions (BSQED contribution of 2.4 eV and 5.2 eV, respectively) of muonic neon atoms in the low-pressure gas phase without bound electrons. Muonic atoms have been recently proposed as an alternative to few-electron high-Z ions for BSQED tests by focusing on circular Rydberg states where nuclear contributions are negligibly small. We determined the - transition energy to be 6297.08 0.04 (stat.) 0.13 (syst.) eV using superconducting transition-edge sensor microcalorimeters (5.2-5.5 eV FWHM resolution), which agrees well with the most advanced BSQED theoretical prediction of 6297.26 eV.