A new method to distinguish hadronically decaying boosted Z bosons from W bosons using the ATLAS detector

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 < pT < 400 GeV in √ s = 8 TeV pp collisions with the ATLAS detector at the LHC. For Zboson 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 pT, hadronically decaying Z bosons. However, the modelling of the tagger inputs for boosted W bosons is studied in data using a t ¯t-enriched sample of events in 20.3 fb−1 of data at √ s = 8 TeV. The inputs are well modelled within uncertainties, which builds confidence in the expected tagger performance.