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

TL;DR

This paper investigates how energy deposited by away side partons in heavy-ion collisions creates shockwaves, affecting correlation structures, and explores how dihadron triggers can reveal the longitudinal extent of these shockwaves.

Contribution

It introduces a method to analyze the longitudinal structure of shockwaves in heavy-ion collisions using dihadron triggers, accounting for biases and energy deposition effects.

Findings

Dihadron triggers help constrain the rapidity of away side partons.

Energy deposition into the medium is often biased towards small amounts.

The correlation structure is significantly affected by fragmentation and energy bias.

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 shockwave (a Mach cone) which leads to away side correlation strength at large angles. A prediction following from assuming such a hydrodynamical origin of the correlation structure is that there is a sizeable elongation of the shockwave in rapidity due to the longitudinal expansion of the bulk medium. Using a single hadron trigger, this cannot be observed due to 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 which change the correlation structure substantially: There is not only a sizeable contribution due to the fragmentation of the emerging away side parton, but also a systematic bias towards small energy deposition into the medium and hence a weak shockwave. In this paper, both effects are addressed.