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

This letter presents a measurement of the nuclear modification factor oflarge-radius jets in $\sqrt{s_\mathrm{NN}} = 5.02$ TeV Pb+Pb collisions by theATLAS experiment. The measurement is performed using 1.72 nb$^{-1}$ and 257pb$^{-1}$ of Pb+Pb and $pp$ data, respectively. The large-radius jets arereconstructed 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 thetransverse momentum ($p_{\mathrm{T}}$) kinematic range of $158 < p_{\mathrm{T}}< 1000$ GeV and absolute pseudorapidity $|y|<2.0$. The large-radius jetconstituents are further re-clustered using the $k_{t}$ algorithm in order toobtain the splitting parameters, $\sqrt{d_{12}}$ and $\Delta R_{12}$, whichcharacterize the transverse momentum scale and angular separation for thehardest 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 significantdifference in the quenching of large-radius jets having single sub-jet andthose with more complex substructure is observed. Systematic comparison of jetsuppression in terms of $R_{\mathrm{AA}}$ for different jet definitions is alsoprovided. Presented results support the hypothesis that jets with hard internalsplittings lose more energy through quenching and provide a new perspective forunderstanding the role of jet structure in jet suppression.