Angular Structure of Jet Quenching Within a Hybrid Strong/Weak Coupling Model

TL;DR

This paper investigates how jet quenching affects the angular distribution of energy within jets in heavy ion collisions using a hybrid model that incorporates transverse momentum broadening and medium response, revealing new observable sensitivities.

Contribution

It introduces a parameter for transverse momentum broadening in a hybrid model and proposes a new jet shape ratio observable to detect its effects.

Findings

Jets are narrower after quenching, even with broadening effects.

Standard observables are insensitive to transverse momentum broadening.

A new jet shape ratio observable reveals broadening effects.

Abstract

Within the context of a hybrid strong/weak coupling model of jet quenching, we study the modification of the angular distribution of the energy within jets in heavy ion collisions, as partons within jet showers lose energy and get kicked as they traverse the strongly coupled plasma produced in the collision. To describe the dynamics transverse to the jet axis, we add the effects of transverse momentum broadening into our hybrid construction, introducing a parameter $K\equiv \hat q/T^3$ that governs its magnitude. We show that, because of the quenching of the energy of partons within a jet, even when $K\neq 0$ the jets that survive with some specified energy in the final state are narrower than jets with that energy in proton-proton collisions. For this reason, many standard observables are rather insensitive to $K$. We propose a new differential jet shape ratio observable in which the effects of transverse momentum broadening are apparent. We also analyze the response of the medium to the passage of the jet through it, noting that the momentum lost by the jet appears as the momentum of a wake in the medium. After freezeout this wake becomes soft particles with a broad angular distribution but with net momentum in the jet direction. We show that the particles coming from the response of the medium to the momentum and energy deposited in it leads to a correlation between the momentum of soft particles well separated from the jet in angle with the direction of the jet momentum, and find qualitative but not quantitative agreement with experimental data on observables designed to extract such a correlation. By confronting the results that we obtain upon introducing transverse momentum broadening and the response of the medium to the jet with available jet data, we highlight the importance of these processes for understanding the internal, soft, angular structure of high energy jets.