Physics (Internal)

The Proton Remains Puzzling

This event is part of the Physics Department Colloquia Series.

Nucleons are building blocks of visible matter, and are responsible for more than 99% of the visible mass in the universe. While major progress has been made in the last two decades in understanding the proton spin puzzle discovered in the late 1980s by the European Muon Collaboration, a new proton puzzle developed in the last several years concerning the proton charge radius, which is the charge weighted size of the proton. The ultrahigh precise value of the proton charge radius determined from muonic hydrogen Lamb shift measurements is about 7 sigma smaller than the values determined from electron-proton scattering experiments and CODATA value of the hydrogen Lamb shift measurements. In this talk I will review the latest situation concerning the proton charge radius and discuss upcoming new experiments addressing this puzzle.