Even point fermions have a some structure due to the constant radiation and absorption of photons. Protons and neutron do not have point particle dipole moments because they are not point particles. J i where the sum is over all the constuents.
Magnetic moments provide indirect but very powerful information about particle structure.
Even in the undergraduate lab, measurements of Electron spin resonance and Nuclear magnetic resonance indicate that electrons are point particles and protons are not. Scattering experiments are used to directly measure the size and substructure of particles. In order to resolve this issue more data and more detailed analysis are necessary. N 0 be the number of balls incident per unit area of the target.