Measurement of the Lund jet plane in hadronic decays of top quarks and W bosons with the ATLAS detector

Abstract

The Lund jet plane (LJP) ismeasured for the firsttime in t -t events, using 140 fb-1 of SQUARE ROOTs = 13 TeV pp collisiondata collected with the ATLAS detector at the LHC. TheLJP is a two-dimensional observable of the sub-structure ofhadronic jets that acts as a proxy for the kinematics of partonshowers and hadron formation. The observable is constructedfrom charged particles and is measured for R = 1.0 anti-ktjets with transverse momentum above 350 GeV containingthe full decay products of either a top quark or a daughterW boson. The other top quark in the event is identified fromits decay into a b-quark, an electron or a muon and a neutrino.The measurement is corrected for detector effects andcompared with a range of Monte Carlo predictions sensitiveto different aspects of the hadronic decays of the heavy particles.In the W-boson-initiated jets, all the predictions areincompatible with themeasurement. In the top quark initiatedjets, disagreement with all predictions is observed in smallersubregions of the plane, and with a subset of the predictionsacross the fiducial plane. The measurement could be usedto improve the tuning of Monte Carlo generators, for bettermodelling of hadronic decays of heavy quarks and bosons,or to improve the performance of jet taggers.