After years of confusion, a new study confirms the proton is tinier than once thought. That enables a test of the standard model of particle physics.

Puzzling problem: Karsten Schuhmann (left) and Aldo Antognini of the Paul Scherrer Institute inspect the laser system that was used for the laser spectroscopy measurements on muonic deuterium.

The PRad physics experiment studies how electrons scatter off of protons A scientific tug-of-war is underway over the size of the proton. Scientists can’t agree on how big the subatomic particle is, ...

Physicists get closer to solving the proton radius puzzle with unique new measurement of the charge radius of the proton Textbook pictures make atomic nuclei seem tidy, but they are actually fuzzy ...