Support for the Reality of Quarks

There are still some doubts about the existence of quarks among a minority ofphysicists who believe that they could merely represent a symmetry withouthaving a physical reality. This is because a rigorous element of reality for quarkscan only correspond to free observed quarks. An independent argument in favorof the existence of quarks as real particles is given using a method based onMayer's cluster expansion to calculate the critical temperature for a phasetransition of a nonideal quark=nantiquark plasma to a hadron fluid.