New Measurement of Proton Radius 0.87fm Intensifies Proton Radius Puzzle

[1801.08816] New measurement of the $1S-3S$ transition frequency of hydrogen: contribution to the proton charge radius puzzle

Abstract: We present a new measurement of the $1S-3S$ two-photon transition frequency of hydrogen, realized with a continuous-wave excitation laser at 205 nm on a room-temperature atomic beam, with a relative uncertainty of $9\times10^{-13}$. The proton charge radius deduced from this measurement, $r_\text{p}=0.877(13)$ fm, is in very good agreement with the current CODATA-recommended value.