The Size Of The Proton And The Deuteron

We have recently measured the 2S(1/2)(F=1) - 2P(3/2)(F=2) energy splitting in the muonic hydrogen atom mu p 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 r(p) = 0.84184 (67) fm. This value is ten times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of r(p) = 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 r(p) we obtain improved values of the Rydberg constant, R infinity = 10973731.568160 (16) m(-1), and the rms charge radius of the deuteron r(d) = 2.12809 (31) fm.