Misura del Lamb shift nell'idrogeno muonico e il Proton Radius Puzzle

The proton radius puzzle is an unsolved problem relating to the charge radius of the proton. More than 99% of the observable matter in the universe is made up of protons and neutrons, the components of atomic nuclei. Thus, accurate knowledge of the proton charge radius is essential to our comprehension of how matter behaves. Historically, the proton charge radius was measured by two independent methods, hydrogen spectroscopy and electron-proton scattering. In 2010, the CREMA collaboration led by Dr. Pohl performed a ultraprecise determination of the proton charge radius from muonic hydrogen Lamb shift measurements using pulsed laser spectroscopy. The experiment was performed at the proton accelerator at the Paul Scherrer institute, in Switzerland. The resulting radius differed by 5.0 standard deviations from the 2006-CODATA value. A new measurement in 2013 obtained a value that differed by about 7 standard deviations from the 2010-CODATA value. The puzzle remains unanswered today and is an active area of research.