Mach cones and dijets - jet quenching and fireball expansion dynamics

Abstract

The energy loss of a hard parton is regarded as a useful tool to probe properties of a soft medium. However, the information obtained by a measurement of the nuclear suppression R_AA is not very sensitive to medium properties. Thus, more differential observables are needed. Here we focus on the pattern of angular correlation of hadrons associated with a hard trigger. These show rich pattern when going from low p_T to high p_T associate momentum. At low p_T, the pattern of associate hadrons can be understood in terms of Mach shocks excited by the energy lost from the away side parton while the parton itself is absorbed by the medium. At high p_T, fluid dynamics is not applicable any more and the correlations become dominated by the punchtrough of the away side parton with subsequent fragmentation. We present an analysis of these phenomena taking into account the full expansion dynamics of soft matter and show how both transverse and longitudinal expansion play a crucial role in understanding the data.