Measurement of Suppression of Large-Radius Jets and Its Dependence on Substructure in Pb+Pb Collisions at √sNN=5.02 TeV with the ATLAS Detector

Abstract

This letter presents a measurement of the nuclear modification factor of large-radius jets in √sNN=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-kt algorithm using a radius parameter of R=1.0, by reclustering anti-kt R=0.2 jets, and are measured over the transverse momentum (pT) kinematic range of 158<pT<1000 GeV and absolute pseudorapidity |y|<2.0. The large-radius jet constituents are further reclustered using the kt algorithm in order to obtain the splitting parameters, √d12 and ΔR12, which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, RAA, obtained by comparing the Pb+Pb jet yields to those in pp collisions, is measured as a function of jet transverse momentum (pT) and √d12 or ΔR12. A significant difference in the quenching of large-radius jets having single subjet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of RAA 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.