Measurement of suppression of large-radius jets and its dependence on substructure in Pb+Pb at 5.02 TeV by ATLAS detector

This note presents 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 having transverse momenta, $p_{\mathrm{T}} > 35$~\GeV. After applying a trimming procedure, the large-radius jet constituents are re-clustered using the $k_{t}$ algorithm in order to obtain the splitting parameter, $\sqrt{d_{12}}$, which characterizes the transverse momentum scale for the hardest splitting in the jet. The yield of the $R = 1.0$ jets is measured as a function of $p_{\mathrm{T}}$ and $\sqrt{d_{12}}$ over the rapidity and transverse momentum ranges, $|y| < 2$ and $156 < p_{\mathrm{T}} < 1000$ GeV, 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 and $\sqrt{d_{12}}$. A significant evolution of $R_{\mathrm{AA}}$ with $\sqrt{d_{12}}$ is observed at small $\sqrt{d_{12}}$ values, indicating a significant difference in the quenching of large-radius jets having single sub-jet and those with more complex substructure. The inclusive jet $R_{\mathrm{AA}}$, integrated over $\sqrt{d_{12}}$, is qualitatively similar to that obtained in previous measurements for $R=0.4$ jets.