Physical Review A - Atomic, Molecular, and Optical Physics
The Lamb shift in helium ions were investigated to verify or remove a discrepancy between theory and experiment by the anisotropy method. The method was used for the elimination of residual polarization sensitivity of the photon detectors. The results showed that the experimental value of a Lamb shift were in agreement with the theoretical values.
Van Wijngaarden, A.; Holuj, F.; and Drake, Gordon W. F.. (2001). Lamb shift in He+: Resolution of a discrepancy between theory and experiment. Physical Review A - Atomic, Molecular, and Optical Physics, 63 (1), 12505-12501.