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

TL;DR

This paper introduces a likelihood-based method using jet mass, charge, and b-tagging to distinguish hadronically decaying boosted Z bosons from W bosons in ATLAS data, improving identification efficiency.

Contribution

The paper develops a new discriminant technique combining multiple variables to differentiate Z from W bosons, validated through simulation and data modeling.

Findings

Achieves high W boson rejection at various Z tagging efficiencies.

Model inputs are well represented in data, supporting method reliability.

Demonstrates potential for improved boson identification in LHC analyses.

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 $W'\rightarrow WZ$ for bosons in the transverse momentum range 200 GeV $<p_{T}<$ 400 GeV in $\sqrt{s}=8$ TeV $pp$ collisions with the ATLAS detector at the LHC. For $Z$-boson tagging efficiencies of $\epsilon_Z=$ 90%, 50%, and 10%, one can achieve $W^+$-boson tagging rejection factors ($1/\epsilon_{W^+}$) 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 $t\bar{t}$-enriched sample of events in 20.3 fb$^{-1}$ of data at $\sqrt{s}=8$ TeV. The inputs are well modelled within uncertainties, which builds confidence in the expected tagger performance.