Z-scaling and A-dependence of fractality of direct photon production in p-A collisions

The A-dependence of the fractal dimension α of direct photon production in pp- and pBe-collisions at high energies is studied. The scaling function H (z) for the processes is calculated. The power behaviour of the scaling function, H (z) ∼ z-α, describing the photon formation mechanism for pBe- and pp-collisions, is established. The fractal dimension of photon formation is found to be the same for both pp → γ X and pBe →γ X processes: αpBe ≅ αpp. One can conclude that nuclear matter intensifies the photon formation and does not change the fractal dimension. Based on the universality of the scaling function for pBe-collisions, the Ed3σ / dq3 dependence on transverse momentum at energies √ s = 63, 200, 500 GeV is predicted. The obtained results can be of interest for future experiments planned at RHIC (BNL), LHC (CERN), HERA (DESY) and Tevatron (Batavia) to search for new phenomena in hadron-nucleus and nucleus-nucleus collisions