Measurement of suppression of large-radius jets and its dependence on substructure in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV with the ATLAS detector

TL;DR

This study measures how large-radius jets are suppressed in lead-lead collisions at 5.02 TeV, revealing that jets with complex substructure experience more quenching, offering insights into jet-medium interactions in quark-gluon plasma.

Contribution

It introduces a detailed analysis of jet substructure dependence of jet suppression in heavy-ion collisions using ATLAS data, highlighting the role of internal splittings in energy loss.

Findings

Jets with complex substructure are more suppressed.

Jet quenching depends on internal splitting parameters.

Results support that harder internal splittings lead to greater energy loss.

Abstract

This letter presents a measurement of the nuclear modification factor of large-radius jets in $\sqrt{s_\mathrm{NN}} = 5.02$ TeV Pb+Pb collisions by the ATLAS experiment. The measurement is performed using 1.72 nb$^{-1}$ and 257 pb$^{-1}$ of Pb+Pb and $pp$ data, respectively. The large-radius jets are reconstructed with the anti-$k_{t}$ algorithm using a radius parameter of $R = 1.0$, by re-clustering anti-$k_{t}$ $R = 0.2$ jets, and are measured over the transverse momentum ($p_{\mathrm{T}}$) kinematic range of $158 < p_{\mathrm{T}} < 1000$ GeV and absolute pseudorapidity $|y|<2.0$. The large-radius jet constituents are further re-clustered using the $k_{t}$ algorithm in order to obtain the splitting parameters, $\sqrt{d_{12}}$ and $\Delta R_{12}$, which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, $R_{\mathrm{AA}}$, obtained by comparing the Pb+Pb jet yields to those in $pp$ collisions, is measured as a function of jet transverse momentum ($p_{\mathrm{T}}$) and $\sqrt{d_{12}}$ or $\Delta R_{12}$. A significant difference in the quenching of large-radius jets having single sub-jet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of $R_{\mathrm{AA}}$ for different jet definitions is also provided. Presented results support the hypothesis that jets with hard internal splittings lose more energy through quenching and provide a new perspective for understanding the role of jet structure in jet suppression.