Professor Amanda Cooper-Sarkar

Abstract:

This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, e^{±}μ^{∓}, e^{±}τ^{∓}, or μ^{±}τ^{∓} using 20.3  fb^{-1} of pp collision data at sqrt[s]=8  TeV collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the standard model expectations. Limits are set on the cross section of new phenomena in two scenarios: the production of ν[over ˜]_{τ} in R-parity-violating supersymmetric models and the production of a lepton-flavor-violating Z^{'} vector boson.

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.