The size of the proton
Pohl, Randolf and Antognini, Aldo and Nez, Francois and Amaro, Fernando and Biraben, Francois and Cardoso, Joao and Covita, Daniel and Dax, Andreas and Dhawan, Satish and Fernandes, Luis and Giesen, Adolf and Graf, Thomas and Hänsch, Theodor and Indelicato, Paul and Julien, Lucile and Kao, Cheng-Yang and Knowles, Paul and Le Bigot, Eric and Liu, Yi-Wei and Lopes, Jose and Ludhova, Livia and Monteiro, Christina and Mulhauser, Francoise and Nebel, Tobias and Rabinowitz, Paul and dos Santos, Joaquim and Schaller, Lukas and Schuhmann, Karsten and Schwob, Catherine and Taqqu, David and Veloso, Joao and Kottmann, Franz (2010) The size of the proton. Nature, 466, pp. 213-217. Macmillan Publishers Limited. DOI: 10.1038/nature09250.
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The proton is the primary building block of the visible Universe, but many of its properties—such as its charge radius and its anomalous magneticmoment—are not well understood. The root-meansquare charge radius, rp, has been determined with an accuracy of 2 per cent (at best) by electron–proton scattering experiments. The present most accurate value of rp (with an uncertainty of 1 per cent) is given by the CODATA compilation of physical constants. This value is based mainly on precision spectroscopy of atomic hydrogen and calculations of bound-state quantum electrodynamics. The accuracy of rp as deduced from electron–proton scattering limits the testing of bound-state QED in atomic hydrogen as well as the determination of the Rydberg constant (currently the most accurately measured fundamental physical constant). An attractive means to improve the accuracy in themeasurement of rp is provided bymuonic hydrogen (a proton orbited by a negative muon); its much smaller Bohr radius compared to ordinary atomic hydrogen causes enhancement of effects related to the finite size of the proton. In particular, theLamb shift (the energy difference between the 2S1/2 and 2P1/2 states) is affected by as much as 2 per cent. Here we use pulsed laser spectroscopy to measure a muonic Lamb shift of 49,881.88(76)GHz. On the basis of present calculations of fine and hyperfine splittings and QED terms, we find rp 50.84184(67) fm, which differs by 5.0 standard deviations from the CODATA value of 0.8768(69) fm. Our result implies that either the Rydberg constant has to be shifted by 2110 kHz/c (4.9 standard deviations), or the calculations of the QED effects in atomic hydrogen or muonic hydrogen atoms are insufficient.
|Title:||The size of the proton|
|Date:||08 July 2010|
|Journal or Publication Title:||Nature|
|In Open Access:||No|
|In ISI Web of Science:||Yes|
|Page Range:||pp. 213-217|
|Publisher:||Macmillan Publishers Limited|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Aeronautics|
|HGF - Program Themes:||L AR - Aircraft Research|
|DLR - Research area:||Aeronautics|
|DLR - Program:||L AR - Aircraft Research|
|DLR - Research theme (Project):||L - Laser Research and Technology|
|Institutes and Institutions:||Institute of Technical Physics|
|Deposited By:||Dr.rer.nat. Hans-Albert Eckel|
|Deposited On:||08 Jul 2010 11:33|
|Last Modified:||26 Mar 2013 13:18|
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