that a large number of pions would be produced if the collision had happened in free space. Clearly, the outgoing quark and gluon fields cannot be represented as asymptotic pion and nucleon states immediately. The fields must expand and become dilute enough to be called real hadrons. If this collision occurs in a high energy density medium, the outgoing quark-gluon fields will encounter other hadrons before they can hadronize. It is reasonable to suppose that this “star burst" will actually be a seed for quark-gluon plasma formation if the surrounding matter is superheated hadronic matter. We need a semi-quantitative model of this physics.

A fundamental result from kinetic theory is that the number of scattering processes of the type 1 + 2 $\rightarrow X$ is given by $$N_{1+2 \rightarrow X}
= \int dt \int d^3 x \int \frac{d^3 p_1}{(2 \pi )^3} \, f_1 ({\bf x},
{\bf p}_1,t) \int \frac{d^3 p_2}{(2 \pi )^3} \, f_2 ({\bf x},{\bf p}_2,t)
\, v_{12} \, \sigma_{1+2 \rightarrow X}(s_{12}) \, .$$ Here $v_{12}$ is a relative velocity, $$v_{12} = \frac{\sqrt{(p_1 \cdot p_2)^2 -m_N^4}}{E_1 \, E_2} \, ,$$ where $p_i$ denotes the four-momentum of nucleon $i$ and $E_i =\sqrt{
{\bf p}_i^2 + m_N^2}$ its energy. The $f_i$ 