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The radius of the proton was calculated using supercomputers such as the high-performance computer MOGON II at JGU. Photo Credit: Stefan F. Sämmer |
Theoretical physicists at Johannes Gutenberg University Mainz (JGU) have once again succeeded in significantly improving their calculations of the electric charge radius of the proton published in 2021. For the first time, they obtained a sufficiently precise result completely without the use of experimental data. With respect to the size of the proton, these new calculations also favor the smaller value. Concurrently, the physicists have published a stable theory prediction for the magnetic charge radius of the proton. All new findings can be found in three preprints published on the arXiv server.
All known atomic nuclei consist of protons and neutrons, yet many of the characteristics of these ubiquitous nucleons remain to be understood. Specifically, despite several years of effort, scientists have been unable to pin down the radius of the proton. In 2010, the result of a new proton radius measurement technique involving laser spectroscopy of muonic hydrogen caused a stir. In this 'special' kind of hydrogen, the electron in the shell of the atom was replaced by its heavier relative, the muon, which is a much more sensitive probe for the proton's size. The experimentalists came up with a significantly smaller value than that found following corresponding measurements of normal hydrogen as well as the traditional method of determining the proton radius using electron-proton scattering. The big question that physicists have been asking ever since is whether this deviation could be evidence for new physics beyond the Standard Model or simply reflects systematic uncertainties inherent to the different measuring methods.