Origins of the di-jet asymmetry in heavy-ion collisions

The di-jet asymmetry—the measure of the momentum imbalance in a di-jet system—is a key jet quenching observable. Using the event generator Jewel we show that the di-jet asymmetry is dominated by fluctuations both in proton–proton and in heavy-ion collisions. We discuss how in proton–proton collisions the asymmetry is generated through recoil and out-of-cone radiation. In heavy-ion collisions two additional sources can contribute to the asymmetry, namely energy loss fluctuations and differences in path length. The latter is shown to be a sub-leading effect. We discuss the implications of our results for the interpretation of this observable.