Abstract

This paper describes the concept, technical realisation and validation of a largely data-driven method to model events with $Z\rightarrow\tau\tau$ decays. In $Z\rightarrow\mu\mu$ events selected from proton--proton collision data recorded at $\sqrt{s}=8$ TeV with the ATLAS experiment at the LHC in 2012, the $Z$ decay muons are replaced by $\tau$ leptons from simulated $Z\rightarrow\tau\tau$ decays at the level of reconstructed tracks and calorimeter cells. The $\tau$ lepton kinematics are derived from the kinematics of the original muons. Thus, only the well-understood decays of the $Z$ boson and $\tau$ leptons as well as the detector response to the $\tau$ 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 $\tau$-embedding method is particularly relevant for Higgs boson searches and analyses in $\tau\tau$ final states, where $Z\rightarrow\tau\tau$ 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 $H\rightarrow\tau\tau$ analysis of the full datataset recorded during 2011 and 2012.

Highlights

  • 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

  • In Z → μ μ events selected from pp collision data recorded with the ATLAS experiment during the LHC Run1, tracks and calorimeter cell energies associated with the Z decay muons are replaced by the corresponding tracks and energy depositions of the τ leptons from simulated Z → ττ decays

Read more

Summary

The ATLAS detector

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

Final-state reconstruction
Event samples
Event selection
Procedure
Merging of data and simulated event
Reconstruction of the embedded events
Special properties of the τ -embedded event samples
Systematic uncertainties
Validation
Findings
Summary and conclusions
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.