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<p>The ATLAS collaboration has introduced and implemented a strategy for selecting, and measuring the properties of, large-radius jets composed from skinny subjets in heavy ion collisions at the LHC. We show how measurements of these jets teach us about the resolution length <i>L</i><sub>res</sub> of quark-gluon plasma (QGP) and can teach us how jet substructure shapes the wakes that jets excite in the droplets of QGP through which they pass. We begin by using Hybrid Model calculations to reproduce experimental measurements published by ATLAS in 2023 of <i>R</i><sub><i>AA</i></sub> for large-radius jets in PbPb collisions, identified via first reconstructing skinny anti-<i>k</i><sub><i>t</i></sub> <i>R</i> = 0.2 subjets and then clustering <i>R</i> = 1 jets using them as constituents. We investigate how <i>R</i><sub><i>AA</i></sub> for these large-radius jets depends on the angle between the two skinny subjets involved in the final reclustering step of the <i>R</i> = 1 jet. We show how these observables depend on <i>L</i><sub>res</sub> and demonstrate that the published ATLAS data rule out <i>L</i><sub>res</sub> = ∞: these data are inconsistent with any picture in which an entire parton shower loses energy coherently as if it were a single colored object. Demonstrating that the QGP can resolve partons within a parton shower is central to the broader program of using jet quenching measurements to probe QGP.</p><p>We make further use of this setup by analyzing the response of the medium to the passage of large-radius <i>R</i> = 2 jets containing two skinny <i>R</i> = 0<i>.</i>2 subjets, produced in gamma-jet events, identified as above. We introduce novel jet-shape observables that allow us to visualize the angular shape of the soft hadrons originating from the wakes that wide jets with two skinny subjets excite in the droplet of QGP, as a function of the angular separation between the subjets. We find that even when the two hard subjets are 0.8 to 1.0 radians apart, a single broad wake is produced. Only when the two subjets are even farther apart is the presence of two sub-wakes revealed. We show that the way in which jet structure shapes jet wakes can be visualized with similar clarity in experimental data by measuring the observables we have introduced using only those hadrons with low transverse momenta. These observables thus offer a new and distinctive way of seeing jet wakes in heavy ion collision data.</p>

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Visualizing how the structure of large-radius jets shapes their wakes

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  • 发表日期：

    2026年1月2日

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  • Arjun Srinivasan Kudinoor,
  • Daniel Pablos,
  • Krishna Rajagopal

摘要

The ATLAS collaboration has introduced and implemented a strategy for selecting, and measuring the properties of, large-radius jets composed from skinny subjets in heavy ion collisions at the LHC. We show how measurements of these jets teach us about the resolution length Lres of quark-gluon plasma (QGP) and can teach us how jet substructure shapes the wakes that jets excite in the droplets of QGP through which they pass. We begin by using Hybrid Model calculations to reproduce experimental measurements published by ATLAS in 2023 of RAA for large-radius jets in PbPb collisions, identified via first reconstructing skinny anti-kt R = 0.2 subjets and then clustering R = 1 jets using them as constituents. We investigate how RAA for these large-radius jets depends on the angle between the two skinny subjets involved in the final reclustering step of the R = 1 jet. We show how these observables depend on Lres and demonstrate that the published ATLAS data rule out Lres = ∞: these data are inconsistent with any picture in which an entire parton shower loses energy coherently as if it were a single colored object. Demonstrating that the QGP can resolve partons within a parton shower is central to the broader program of using jet quenching measurements to probe QGP.

We make further use of this setup by analyzing the response of the medium to the passage of large-radius R = 2 jets containing two skinny R = 0.2 subjets, produced in gamma-jet events, identified as above. We introduce novel jet-shape observables that allow us to visualize the angular shape of the soft hadrons originating from the wakes that wide jets with two skinny subjets excite in the droplet of QGP, as a function of the angular separation between the subjets. We find that even when the two hard subjets are 0.8 to 1.0 radians apart, a single broad wake is produced. Only when the two subjets are even farther apart is the presence of two sub-wakes revealed. We show that the way in which jet structure shapes jet wakes can be visualized with similar clarity in experimental data by measuring the observables we have introduced using only those hadrons with low transverse momenta. These observables thus offer a new and distinctive way of seeing jet wakes in heavy ion collision data.