Abstract
This paper describes the concept, technical realisation and validation of a largely data-driven method to model events with Z→ττ decays. In Z→μμ events selected from proton-proton collision data recorded at √s=8 TeV with the ATLAS experiment at the LHC in 2012, the Z decay muons are replaced by τ leptons from simulated Zarrowττ decays at the level of reconstructed tracks and calorimeter cells. The τ lepton kinematics are derived from the kinematics of the original muons. Thus, only the well-understood decays of the Z boson and τ leptons as well as the detector response to the τ decay products are obtained from simulation. All other aspects of the event, such as the Z boson and jet kinematics as well as effects from multiple interactions, are given by the actual data. This so-called τ-embedding method is particularly relevant for Higgs boson searches and analyses in ττ final states, where Zarrowττ decays constitute a large irreducible background that cannot be obtained directly from data control samples. In this paper, the relevant concepts are discussed based on the implementation used in the ATLAS Standard Model H→ττ analysis of the full datataset recorded during 2011 and 2012.
Highlights
This paper describes the concept, technical realisation and validation of a largely datadriven method to model ev√ents with Z → ττ decays
The detector response to the Z decay muons can be removed from the data events and replaced by corresponding information for τ leptons from simulated Z → ττ decays, where the τ kinematics are derived from the kinematics of the original muons
While the τ-embedded samples constitute a largely data-driven model of Z → ττ events, the τ leptons and their decay products are based on simulation, and systematic uncertainties associated with the Monte Carlo simulated (MC) description of τ decays and the corresponding detector response need to be considered within physics analyses
Summary
The ATLAS detector [14] at the LHC covers nearly the entire solid angle around the collision point It consists of an inner tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroid magnets, each with eight coils. The high-granularity silicon pixel detector covers the vertex region and typically provides three measurements per track. It is followed by the silicon microstrip tracker which usually provides four two-dimensional measurement points per track. These silicon detectors are complemented by the transition radiation tracker, which enables radially extended track reconstruction up to |η| = 2.0. This is followed by two software-based trigger levels which together reduce the event rate to about 400 Hz
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