From mach cone to reappeared jet: What do we learn from PHENIX results   on non-identified jet correlation?
  High $p_T$ jets are known to be strongly modified by the dense, strongly interacting medium created in heavy-ion collisions. The jet signal, extracted from two particle $\Delta\phi$ correlation, shows a systematic evolution of these modifications as function of $p_T$ and centrality. At intermediate $p_T$, both near side and away side correlations are modified. But the modifications are much stronger at the away side, resulting in a characteristic cone type of structure in central Au + Au collisions. The robustness of cone structure is strengthened by studying the jet shape as function of angle relative to the reaction plane. As one increase the $p_T$ for BOTH hadrons, the cone structure seems to be filled up, and a peak structure appears on the away side. However, the interpretation of these results require careful separation of medium effect and surface bias. 
Jiangyong Jia