Visualizing the diffusion wake in high-energy heavy-ion collisions

Diffusion wake accompanying a Mach cone is a unique feature of the medium response to jet-medium interaction inside the quark-gluon plasma in high-energy heavy-ion collisions. It leads to a depletion of soft hadrons in the opposite direction of the propagating jet and has been recently observed in $Z$-jet events of Pb+Pb collisions at LHC. In di-jet events, however, the diffusion wake of one jet usually overlaps with the medium-induced hadron enhancement of other jet without a clear signal except a reduction of the hadron enhancement, unless there is a large rapidity gap between the two jets. We propose to use the rapidity asymmetry of jet-hadron correlations in di-jets with a finite rapidity gap relative to that without, as a robust signal of the diffusion wake. Based on study of diffusion wake in dijets, we further propose a novel method that is free from background subtraction to identify the jet‐induced diffusion wake by computing the hadron rapidity distribution along the $\gamma$ axis in $\gamma$-jet events. This method is experimentally accessible without traditional background corrections. The same approach can be readily applied to di-jet data at RHIC and the LHC by treating the leading (or sub-leading) jet as a "photon proxy" within a fixed rapidity window.