The dynamics of partonic cascades may be an important aspect for particle production in relativistic collisions of nuclei at CERN SPS and BNL RHIC energies. Within the parton-cascade model, we estimate the production of single photons from such cascades due to the scattering of quarks and gluons $q\overrightarrow{g}q\gamma ,$ quark-antiquark annihilation $q\overline{q}\to g\gamma$ or γγ, and electromagnetic bremsstrahlung of quarks $\overrightarrow{q}q\gamma .$ We find that the latter QED branching process plays the dominant role for photon production, similarly as the QCD branchings $\overrightarrow{q}\mathrm{qg}$ and $\overrightarrow{g}\mathrm{gg}$ play a crucial role for parton multiplication. We conclude therefore that photons accompanying the parton-cascade evolution during the early stage of heavy-ion collisions shed light on the formation of a partonic plasma.

• Received 11 February 1998

DOI:https://doi.org/10.1103/PhysRevC.58.1734