Particles smaller than protons are called THE QUARKS
by definition
they are subatomic particles that make up every proton and neutron in existence.
Properties
The quarks are fractionally charged, that is their charges are either 2/3 or -1/3 the charge of the proton. They have been given the names “up” and “down” respectively. The proton is composed of two up quarks and one down quark while the neutron is composed of one up and two down quarks. You can check to see that the charges of the quarks add up correctly. Up and down quarks are said to be two different quark “flavors.” Because the quarks have half-integral spin (like electrons and neutrinos) there cannot be two identical quarks that have the same quantum properties. Quarks have additional property called color charge that can be red, green, or blue. A proton or neutron must have quarks with one of each of the colors so that they add to white, just like ordinary colors do.