Atomic nuclei, composed of protons and neutrons, hide quarks and gluons at their core. These latter particles, still ...

Quarks are the smallest form of matter that we know of. So small, in fact, that studying it in any meaningful way has proven nearly impossible over the past several decades.

Up quarks have a +2/3 charge, and down quarks have a -1/3 charge. If you add and subtract those fractions, you get the +1 charge of a proton. Valence quarks get lots of attention.