Signatures of Mach shocks at RHIC

Abstract

Hard partons propagating through hot and dense matter lose energy, leading to the observed depletion of hard hadron spectra in nucleus–nucleus collisions as compared to scaled proton–proton collisions. This lost energy has to reappear in the medium due to the conservation of energy. Apart from heating the medium, there is the possibility that a propagating collective mode is excited. We outline a formalism that can be used to track the propagation of such a mode through the evolving medium if its dispersion relation is known and to calculate the resulting distortion of hadronic spectra at freeze-out. Using this formalism, we demonstrate within a detailed picture of the evolution of the expanding system and the experimental trigger conditions that the assumption of a sound mode being excited is in line with two particle correlation measurements by PHENIX and STAR for a semi-hard trigger. In this case, the measurement is sensitive to the averaged speed of sound in the hot matter. We also make suggestions how this sensitivity can be improved.