MEASUREMENT OF THE N = 2 LAMB SHIFT IN HE+ BY THE ANISOTROPY METHOD

A high-precision measurement of the 2s 2S1/2-2p 2P1/2 Lamb shift in He+ by the quenching-anisotropy method is reported. The theory and experimental method are described in detail. The measured value of 14042.52+/-0.16 MHz (+/-11 parts per million) rivals the accuracy of Lamb-shift measurements in hydrogen by microwave resonance. By subtracting the known low-order terms in the Lamb shift, we interpret the results as a measurement of the order alpha-(Z-alpha)6mc2 and higher contributions to the electron self-energy G(SE)(Z-alpha). The various contributions to the Lamb shift are discussed, and a revised value for G(SE)(Z-alpha) at low Z is extracted from high-Z calculations. The theoretical value for the Lamb shift is 14042.51 +/- 0.2 MHz, in excellent agreement with experiment. The results provide the most sensitive available determination of G(SE)(Z-alpha) for low Z. Measurements and calculations for hydrogen and other members of the isoelectronic sequence are discussed.