Do nucleons change their size inside a nucleus?
Nuclear physicists have long wondered whether nucleons change their properties when bound inside a nucleus. This possibility was first considered some 20 years ago, when electron scattering from quarks inside a nucleus was discovered to differ significantly from electron scattering from quarks in a free nucleon. Now, data at DOE’s Jefferson Lab, comparing the properties of protons bound inside the Helium-4 nucleus with those of a free proton (a hydrogen nucleus), provide hints that it may be more economical to describe nuclei in terms of nucleons which differ in size from free nucleons. This is the second indication that a nucleus isn’t merely a set of bound nucleons.
