  The scaling properties of direct photon production in pp, barpp and pA
collisions at high energies is reviewed. The experimental data on the cross
sections obtained at ISR, SpS and Tevatron are used in the analysis. The
properties of data z-presentation, the energy and angular independencies, the
power law, and A-dependence are discussed. The use of z-scaling to search for
new physics phenomena in hadron-hadron, hadron-nucleus and nucleus-nucleus
collisions is suggested. The violation of z-scaling characterized by the change
of the fractal dimension is considered as a new and complimentary signature of
a nuclear phase transition. The cross sections of direct photon, pi0- and
eta0-meson production in pp and pPb collisions at RHIC and LHC energies are
predicted.
