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

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.

arXiv comment32 pages in total, author list starting on page 15, 3 figures. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2019-09/

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