The Lamb shift in muonic hydrogen and the proton radius

摘要

By means of pulsed laser spectroscopy applied to muonic hydrogen (μ-p) we have measured the {formula} transition frequency to be 49881.88(76) GHz. By comparing this measurement with its theoretical prediction based on bound-state QED we have determined a proton radius value of r_p = 0.84184 (67) fm. This new value is an order of magnitude preciser than previous results but disagrees by 5 standard deviations from the CODATA and the electron-proton scattering values. An overview of the present effort attempting to solve the observed discrepancy is given. Using the measured isotope shift of the 1S-2S transition in regular hydrogen and deuterium also the rms charge radius of the deuteron r_d = 2.12809 (31) fm has been determined. Moreover we present here the motivations for the measurements of the μ ~4He~+ and μ ~3He~+ 2S-2P splittings. The alpha and triton charge radii are extracted from these measurements with relative accuracies of few 10~(-4). Measurements could help to solve the observed discrepancy, lead to the best test of hydrogen-like energy levels and provide crucial tests for few-nucleon ab-initio theories and potentials.