A Comment on Conical Flow Induced by Heavy-Quark Jets

The suppression of high transverse momentum particles, recently discovered at RHIC, is commonly interpreted as due to parton energy loss. In high energy nuclear collisions, QCD jets would deposit a large fraction of their energy and into the produced matter. The question of how this energy is degraded and whether we can use this phenomenon to probe the properties of the produced matter is now under active discussion. It has been proposed that if this matter, which is now being referred to as a strongly coupled Quark-Gluon Plasma (sQGP), may behave as a liquid with a very small viscosity. In this case, a very specific collective excitation should be produced, called the “conical flow”, similar e.g. to the sonic booms generated by the shock waves produced by supersonic planes. The RHIC experiments seem indeed to be obtaining some indication that the production of particles emitted opposite to a high-pt jet may actually be peaked away from the quenched jet direction, at an angle roughly consistent with the direction expected in case a shock wave is produced (i.e. orthogonal to the Mach cone). In this note we speculate that for tagged heavy-quark jets one may observe a shrinkage of the Mach cone at moderate pt. The experimental observation of such an effect would be a very good test for the validity of the whole picture currently emerging from the study of partonic matter in nuclear collisions.