Quark-gluon plasma formation in heavy-ion collision

To account for the non-equilibrium character of quark-gluon plasma formation in relativistic heavy-ion collisions, it is proposed to use the product of energy density ? and interaction time τ_int (rather than ?) as the critical quantity for plasma formation. In a geometrical model, τ is approximated by the transit time, and ? by the maximum energy density calculated in the center-of-mass frame. For central collisions, an analytical expression for ?·τ is given. As an example, the systems ¹⁶O + ¹⁶O and ²⁰⁸Pb + ²⁰⁸Pb are investigated as functions of c.m. energy, and their respective suitability for plasma formation is discussed.