  A broadened or double humped away-side structure was observed in 2-particle
azimuthal jet-like correlations at RHIC and SPS. This modification can be
explained by conical emission, from either Mach-cone shock waves or Cherenkov
gluon radiation, and by other physics mechanisms, such as large angle gluon
radiation, jets deflected by radial flow and path-length dependent energy loss.
Three-particle jet-like correlations are studied for their power to distinguish
conical emission from other mechanisms. This article discusses Mach-cone shock
waves, Cherenkov gluon radiation and the experimental evidence for conical
emission from RHIC and SPS.
