Abstract
By means of pulsed laser spectroscopy applied to muonic hydrogen (μ - p) we havemeasured the 2S 1/2 F=1 -2P 3/2 F=2 transition frequency to be 49881.88(76)GHz.1 By comparing this measurement with its theoretical prediction 2-7 based on bound-state QED we have determined a proton radius value of r p =0.84184(67) fm. This new value differs by 5.0 standard deviations from the CODATA value of 0.8768(69) fm, 8 and 3 standard deviation from the e-p scattering results of 0.897(18) fm. 9 The observed discrepancy may arise from a computational mistake of the energy levels in μp or H, or a fundamental problem in bound-state QED, an unknown effect related to the proton or the muon, or an experimental error. © 2011 SPIE.