Abstract

A measurement of jet shapes in top-quark pair events using 1.8 fb−1 of sqrt{s} = 7 mbox{TeV} pp collision data recorded by the ATLAS detector at the LHC is presented. Samples of top-quark pair events are selected in both the single-lepton and dilepton final states. The differential and integrated shapes of the jets initiated by bottom-quarks from the top-quark decays are compared with those of the jets originated by light-quarks from the hadronic W-boson decays Wrightarrow qbar{q}' in the single-lepton channel. The light-quark jets are found to have a narrower distribution of the momentum flow inside the jet area than b-quark jets.

Highlights

  • Hadronic jets are observed in large momentum-transfer interactions

  • For differential (ρ) and integrated jet shapes (Ψ ), they are defined as the ratio of the particle-level quantity to the detector-level quantity as described by the Monte Carlo (MC) simulations discussed in Sect. 3, i.e

  • While the detector-level MC includes the background sources described before, the particle-level jets are built using all particles in the signal sample with an average lifetime above 10−11 s, excluding muons and neutrinos

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Summary

Introduction

Hadronic jets are observed in large momentum-transfer interactions. They are theoretically interpreted to arise when partons—quarks (q) and gluons (g)—are emitted in collision events of subatomic particles. Partons evolve into hadronic jets in a two-step process. The first can be described by perturbation theory and gives rise to a parton shower, the second is non-perturbative and is responsible for the hadronisation. The internal structure of a jet is expected to depend primarily on the type of parton it originated from, with some residual dependence on the quark production and fragmentation process. Due to the different colour factors in ggg and qqg vertices, gluons lead to more parton radiation and gluon-initiated jets are expected to be broader than quark-initiated jets

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