Multiple jets and $\gamma$-jet correlation in high-energy heavy-ion collisions

TL;DR

This paper uses the Linear Boltzmann Transport model to analyze gamma-jet correlations in high-energy heavy-ion collisions, revealing how jet-medium interactions affect jet suppression, azimuthal correlation narrowing, and medium response.

Contribution

It introduces a comprehensive analysis of gamma-jet correlations including multiple jets and medium response, advancing understanding of jet quenching mechanisms in quark-gluon plasma.

Findings

Multiple jets significantly influence gamma-jet correlation at low jet pT.

Jet-medium interaction narrows azimuthal gamma-jet correlation.

Jet-induced medium response broadens the gamma-jet profile.

Abstract

$\gamma$-jet production is considered one of the best probes of the hot quark-gluon plasma in high-energy heavy-ion collisions since the direct $\gamma$ can be used to gauge the initial energy and momentum of the associated jet. This is investigated within the Linear Boltzmann Transport (LBT) model for jet propagation and jet-induced medium excitation. With both parton energy loss and medium response from jet-medium interaction included, LBT can describe experimental data well on $\gamma$-jet correlation in Pb+Pb collisions at the Large Hadron Collider. Multiple jets associated with direct $\gamma$ production are found to contribute significantly to $\gamma$-jet correlation at small $p_T^{\rm jet}<p_T^\gamma$ and large azimuthal angle relative to the opposite direction of $\gamma$. Jet medium interaction not only suppresses the leading jet at large $p_T^{\rm jet}$ but also sub-leading jets at large azimuthal angle. This effectively leads to the narrowing of $\gamma$-jet correlation in azimuthal angle instead of broadening due to jet-medium interaction. The $\gamma$-jet profile on the other hand will be broadened due to jet-medium interaction and jet-induced medium response. Energy flow measurements relative to the direct photon is illustrated to reflect well the broadening and jet-induced medium response.