Size of helium nucleus measured more precisely than ever before

In experiments at the Paul Scherrer Institute PSI, an international research collaboration has measured the radius of the atomic nucleus of helium five times more precisely than ever before. With the aid of the new value, fundamental physical theories can be tested and natural constants can be determined even more precisely. For their measurements, the researchers needed muons--these particles are similar to electrons but are around 200 times heavier. PSI is the only research site in the world w...