Au-Au collisions at $\sqrt s=200$ GeV at the periphery of a nucleus. They move in opposite directions if produced in head-on collisions of partons with equal energies. The trigger parton immediately escapes the nucleus and, therefore, is detected as the “in-vacuum” jet. The companion (away-side) jet traverses the whole nucleus before it comes out. It is modified by “in-medium” effects.

These features can be interpreted in the following way. Beside normal jet fragmentation, the parton impact on the medium initiates emission of Cherenkov gluons which produce a ring of hadrons in the plane perpendicular to the away-side jet axis. Ring’s plane is perpendicular both to the trigger momentum and to the collision plane in which momenta of the colliding particles and the trigger are placed. The two-bump structure results due to the one-dimensional projection of the ring on the azimuthal plane. The analogous two-bump structure was shown by Cherenkov in his earlier papers [@cher] (see also Fig. 1.8 in [@jel]). It is clear that projection of a ring on its diameter in the azimuthal plane is not the best one to reveal its properties. The Proposal 1 uses better (circular) projection of the ring. The shapes of two- and three-particle 