Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen

• DOI: 10.1126/science.1230016
• Publication Date: 2013-01-24T20:49:59Z
• Authors: Aldo Antognini; François Nez; Karsten Schuhmann; Fernando D. Amaro; François Biraben; João M. R. Cardoso; Daniel S. Covita; Andreas Dax; Satish Dhawan; Marc Diepold; Luis M. P. Fernandes; Adolf Giesen; Andrea L. Gouvea; Thomas Graf; Theodor W. Hänsch; Paul Indelicato; Lucile Julien; Cheng-Yang Kao; Paul Knowles; Franz Kottmann; Eric-Olivier Le B...; Yi-Wei Liu; José A. M. Lopes; Livia Ludhova; Cristina M. B. Mo...; Françoise Mulhauser; Tobias Nebel; Paul Rabinowitz; Joaquim M. F. dos...; Lukas A. Schaller; Catherine Schwob; David Taqqu; João F. C. A. Veloso; Jan Vogelsang; Randolf Pohl
• Keywords: Proton Structure; 0103 physical sciences; 7. Clean energy; 01 natural sciences; Muonic Hydrogen

Proton Still Too Small

Despite a proton's tiny size, it is possible to measure its radius based on its charge or magnetization distributions. Traditional measurements of proton radius were based on the scattering between protons and electrons. Recently, a precision measurement of a line in the spectrum of muonium—an atom consisting of a proton and a muon, instead of an electron—revealed a radius inconsistent with that deduced from scattering studies.

Antognini et al.

(p. 417 ; see the Perspective by

Margolis

) examined a different spectral line of muonium, with results less dependent on theoretical analyses, yet still inconsistent with the scattering result; in fact, the discrepancy increased.