The Rydberg constant and proton size from atomic hydrogen.

Beyer, Axel; Maisenbacher, Lothar; Matveev, Arthur; Pohl, Randolf; Khabarova, Ksenia; Grinin, Alexey; Lamour, Tobias; Yost, Dylan C et al. · Science · 2017

basic_science · Level V

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Abstract

At the core of the "proton radius puzzle" is a four-standard deviation discrepancy between the proton root-mean-square charge radii (<i>r</i><sub>p</sub>) determined from the regular hydrogen (H) and the muonic hydrogen (µp) atoms. Using a cryogenic beam of H atoms, we measured the 2S-4P transition frequency in H, yielding the values of the Rydberg constant <i>R</i><sub>∞</sub> = 10973731.568076(96) per meterand <i>r</i><sub>p</sub> = 0.8335(95) femtometer. Our <i>r</i><sub>p</sub> value is 3.3 combined standard deviations smaller than the previous H world data, but in good agreement with the µp value. We motivate an asymmetric fit function, which eliminates line shifts from quantum interference of neighboring atomic resonances.