A New Method to Distinguish Hadronically Decaying Boosted Z Bosons from W Bosons Using the ATLAS Detector

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Abstract

The distribution of particles inside hadronic jets produced in the decay of boosted W and Z bosons can be used to discriminate such jets from the continuum background. Given that a jet has been identified as likely resulting from the hadronic decay of a boosted W or Z boson, this paper presents a technique for further differentiating Z bosons from W bosons. The variables used are jet mass, jet charge, and a b-tagging discriminant. A likelihood tagger is constructed from these variables and tested in the simulation of W′ → WZ for bosons in the transverse momentum range 200 GeV < p_T < 400 GeV in √s̅ = 8 TeV pp collisions with the ATLAS detector at the LHC. For Z-boson tagging efficiencies of Z= 90 , 50, and 10 % , one can achieve W⁺-boson tagging rejection factors (1 / ∈_{W⁺}) of 1.7, 8.3 and 1000, respectively. It is not possible to measure these efficiencies in the data due to the lack of a pure sample of high p_T, hadronically decaying Z bosons. However, the modelling of the tagger inputs for boosted W bosons is studied in data using a tt̅ -enriched sample of events in 20.3 fb⁻¹ of data at √s̅ = 8 TeV. The inputs are well modelled within uncertainties, which builds confidence in the expected tagger performance.

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Keywords

Jets (Nuclear physics), Transverse momentum, W bosons, Z bosons, Causality (Physics), Hadrons—Decay, Branching ratios (Nuclear physics), Mass (Physics), Proton-proton interactions, Leptons (Nuclear physics)

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CC BY 4.0 (Attribution), ©2016 CERN, for the ATLAS Collaboration

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