The question of whether it makes sense to say quarks really exist if you can never isolate one was a controversial issue in the years after the quark model was first proposed.
A relativistic quark model based on the quasipotential approach in quantum field theory is briefly introduced, and by using this model, heavy quarkonium mass spectra are calculated in detail.
The model that we adopted is derived from jet fragmentation functions' field theoretical formulation and the constituent quark model of hadron structure.