Those are rather mysterious objects. Any calculation that any of us has ever done in QCD manipulates with these characters, but they have never been seen in experiments by themselves.
Common wisdom has it that the quarks and gluons are confined by long range forces.
We don't have however a satisfactory understanding of these forces, and this is one of the main questions that interest me. The curious thing about relativistic quantum field theory is that the number of particles is not preserved under Lorentz transformation. And since all these animals interacts strongly, your proton has much stronger interactions at high than at low energies. My publications from qspires. Back to my home page .