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

Abstract

$γ$-jet production is considered one of the best probes of the hot quark-gluon plasma in high-energy heavy-ion collisions since the direct $γ$ 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 $γ$-jet correlation in Pb+Pb collisions at the Large Hadron Collider. Multiple jets associated with direct $γ$ production are found to contribute significantly to $γ$-jet correlation at small $p_T^{\rm jet}<p_T^γ$ and large azimuthal angle relative to the opposite direction of $γ$. 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 $γ$-jet correlation in azimuthal angle instead of broadening due to jet-medium interaction. The $γ$-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.

11 pages with 12 figures, revised version includes discussions on the background subtraction and different definitions of jet profile