The size of the Proton and the Deuteron

Abstract

We have recently measured the 2S1/2F=1 - 2P 3/2F2 energy splitting in the muonic hydrogen atom μp to be 49881.88 (76) GHz. Using recent QED calculations of the fine-, hyperfine, QED and finite size contributions we obtain a root-mean-square proton charge radius of rp 0.84184 (67) fm. This value is ten times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of rp 0.8768 (69) fm. The source of this discrepancy is unknown. Using the precise measurements of the 1S-2S transition in regular hydrogen and deuterium and our value of rp we obtain improved values of the Rydberg constant, R 10973731.568160 (16) m-1and the rms charge radius of the deuteron rd 2.12809 (31) fm. © Published under licence by IOP Publishing Ltd.