Abstract
The proton charge distribution radius is a nuclear physics related observable. QED calculations involve its value. It depends on Lamb shift and hyperfine splitting which experimentally measured, are considered tests of QED, involving Rydberg and fine structure constant. The CREMA collaboration measured proton radius by using muonic hydrogen spectroscopy. Muon, which is 200 times heavier than electron, orbits close to nucleus offering a unique probe for proton structure. They obtained a precise measurement of proton radius but 5% smaller than one from hydrogen spectroscopy and electron-proton scattering. This discrepancy, called the proton radius and it is still an unanswered problem. There is another proton observable, related to both charge and magnetic distribution, called Zemach radius. This is dependent on QED and is strictly related to hyperfine splitting. Different methods for measuring Zemach radius are not in agreement and so far, a precise estimation of this observable for muonic hydrogen doesn't exist. In this context, FAMU, aims to measure hyperfine splitting of muonic hydrogen in ground state which allows a level of uncertainty better than 1%. This will result in first precise measurement of Zemach radius with muonic hydrogen spectroscopy. Adding an independent precise measurement of Zemach radius in current panorama should give a hint to proton radius puzzle solution. Moreover, it will influence nuclear structure theories of simple atoms and act as a precise test of QED. The physical processes behind these measurements are related to muonic atomic physics. In particular, ability of muonic hydrogen to transfer its muon to nearby heavy atoms when in a gaseous mixture. The rate of this transfer process was found to be energy dependent for some elements.
Published Version
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