  We argue that multi-particle production in high energy hadron and nuclear
collisions can be considered as proceeding through the production of gluons in
the background classical field. In this approach we derive the gluon spectrum
immediately after the collision and find that at high energies it is
parametrically enhanced by ln(1/x) with respect to the quasi-classical result
(x is the Bjorken variable). We show that the produced gluon spectrum becomes
thermal (in three dimensions) with an effective temperature determined by the
saturation momentum Qs, T= c Qs/2pi during the time ~1/T; we estimate
c=sqrt{2pi}/2 ~ 1.2. Although this result by itself does not imply that the
gluon spectrum will remain thermal at later times, it has an interesting
applications to heavy ion collisions. In particular, we discuss the possibility
of Bose-Einstein condensation of the produced gluon pairs and estimate the
viscosity of the produced gluon system.
