When a new state of matter called quark-gluon plasma (QGP) is formed in high-energy heavy-ion collisions, energetic quarks or gluons can also be produced that propagate through QGP at the speed of light. They interact strongly with QGP and lose energy, leading to a phenomenon called “jet quenching”. More interestingly, the lost energy during jet propagation cannot disappear, it dissipates and propagates like a sound wave. Since jets’ velocity is much bigger than the speed of sound in QGP, the sound wave is a sonic boom, much like what a supersonic fight jet generates in the air. Such a Mach-cone-like medium response is a direct consequence of jet-medium interaction and is closely related to properties of QGP. It is considered as a key to unraveling the mystery of strong interaction. How to identify and extract the signal of the Mach-cone is one of the most important challenges in the theoretical and experimental studies of high-energy heavy-ion collisions.
Jet-induced Mach-cone, diffusion wake and their effect on jet-hadron correlation in di-jets with large rapidity gap
Recently, Prof. Xin-Nian Wang and Dr. Zhong Yang, a recent PhD recipient at Central China Normal University (CCNU), have discovered a unique signal of the jet-induced Mach-cone-like medium response. The result is published recently in Physical Review Letters 135，072302 （2025） https://doi.org/10.1103/vv7y-xbrc）。
In heavy-ion collisions, the effect of the Mach-cone medium response is very similar to the medium-induced gluon radiation, making it a challenge to separate these two effects. However, the diffusion wake left behind by a propagating jet is a unique phenomenon accompanying the Mach-cone. Searching for the diffusion wake can therefore provide direct evidence of the jet-induced medium response. Wang and Yang calculated the jet-hadron correlation in dijet events with different rapidity-gaps. They discover that the difference in jet-hadron correlation with different dijet rapidity gap is asymmetric. This asymmetry is a unique signal of the diffusion wake in di-jet events. Such asymmetry persists using the mix-event analysis and can be measured background-free. Using this asymmetry one can extend the study of diffusion wake to more frequent dijet events, advancing the experimental measurements of the diffusion wake and our understanding of QGP properties.
As a member of Prof. Wang’s team at CCNU, Yang has focused his PhD study on jet transport and medium response in heavy-ion collisions. This is his 4th article in Phys. Rev. Letters on such topics. He has won the support of China’s Innovational Postdoctoral Grant (博新) and is now a postdoctoral fellow at Vanderbilt University in the US. This work is supported by National Science Foundation of China, Postdoctoral Fellowship Program and the China Postdoctoral Science Foundation and Guangdong MPBAR.
