Measurement of substructure-dependent jet suppression in Pb-Pb collisions at 5.02 TeV with the ATLAS detector

The ATLAS detector at the Large Hadron Collider has been used to measure jet substructure modification and suppression in Pb+Pb collisions at a nucleon–nucleon center-of-mass energy √𝑠𝑁⁢𝑁 = 5.02TeV in comparison with proton–proton (𝑝⁢𝑝) collisions at √𝑠 = 5.02TeV. The Pb+Pb data, collected in 2018, have an integrated luminosity of 1.72nb⁻¹, while the 𝑝⁢𝑝 data, collected in 2017, have an integrated luminosity of 260pb⁻¹. Jets used in this analysis are clustered using the anti-𝑘𝑡 algorithm with a radius parameter 𝑅=0.4. The jet constituents, defined by both tracking and calorimeter information, are used to determine the angular scale 𝑟g of the first hard splitting inside the jet by reclustering them using the Cambridge–Aachen algorithm and employing the soft-drop grooming technique. The nuclear modification factor, 𝑅𝐴⁢𝐴, used to characterize jet suppression in Pb+Pb collisions, is presented differentially in 𝑟g, jet transverse momentum, and in intervals of collision centrality. The 𝑅𝐴⁢𝐴 value is observed to depend significantly on jet 𝑟g. Jets produced with the largest measured 𝑟g are found to be twice as suppressed as those with the smallest 𝑟g in central Pb+Pb collisions. The 𝑅𝐴⁢𝐴 values do not exhibit a strong variation with jet 𝑝T in any of the 𝑟g intervals. The 𝑟g and 𝑝T dependence of jet 𝑅𝐴⁢𝐴 is qualitatively consistent with a picture of jet quenching arising from coherence and provides the most direct evidence in support of this approach.