  The formation of trapped surfaces in the head-on collision of shock waves in
conformal and non-conformal backgrounds is investigated. The backgrounds in-
clude all interesting confining and non-confining backgrounds that may be
relevant for QCD. Several transverse profiles of the shocks are investigated
including distributions that fall-off as powers or exponentials. Different ways
of cutting-off the UV contributions (that are expected to be perturbative in
QCD) are explored. Under some plausible simplifying assumptions our estimates
are converted into predictions for multiplicities for heavy-ion collisions at
RHIC and LHC.
