Measurement of suppression of large-radius jets and its dependence on substructure in Pb+Pb collisions at √s_NN=5.02 TeV with the ATLAS detector

This letter presents a measurement of the nuclear modification factor of large-radius jets in √𝑠_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 kinematic range of 158 < 𝑝_T < 1000 GeV and |𝑦| < 2.0. The large-radius jet constituents are further re-clustered 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, 𝑅_AA, obtained by comparing the Pb+Pb jet yields to those in 𝑝𝑝 collisions, is measured as a function of jet transverse momentum (𝑝_T) and √𝑑₁₂ or Δ𝑅₁₂. 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_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.