Energy deposition in hard dihadron triggered events in heavy-ion collisions

Abstract

The experimental observation of hadrons correlated back-to-back with a (semi-)hard trigger in heavy-ion collisions has revealed a splitting of the away side correlation structure in a low to intermediate transverse momentum (${P}_{T}$) regime. This is consistent with the assumption that energy deposited by the away side parton into the bulk medium produced in the collision excites a sonic shock wave (a Mach cone) that leads to away side correlation strength at large angles. A prediction that follows from assuming such a hydrodynamical origin of the correlation structure is that there is a sizable elongation of the shock wave in rapidity due to the longitudinal expansion of the bulk medium. Using a single-hadron trigger, this cannot be observed because of the unconstrained rapidity of the away side parton. Using a dihadron trigger, the rapidity of the away side parton can be substantially constrained and the longitudinal structure of the away side correlation becomes accessible. However, in such events several effects occur that change the correlation structure substantially: There is not only a sizable contribution due to the fragmentation of the emerging away side parton but also a systematic bias toward small energy deposition into the medium and hence a weak shock wave. In this article, both effects are addressed.