Abstract
The measurement of the \(Z \rightarrow \tau \tau \) cross section in proton-proton collisions at the centre of mass energy of 7 TeV with the ATLAS experiment is described in this chapter. The analysis has been performed in three different final states determined by the decay mode of the \(\tau \) lepton. The data sample collected during 2011 corresponding to an integrated luminosity of 1.34–1.55 fb\(^{-1}\) depending on the final state is used.
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Notes
- 1.
The \(\tau \) lepton reconstruction in ATLAS means the reconstruction of the visible part of the hadronically decaying \(\tau \) lepton (\(\tau \rightarrow {\mathrm{hadrons }} + \nu _\tau \)) where the visible part is built by the hadrons from the \(\tau \) decay. More details about the \(\tau \) lepton decays are given in Sect. 5.2.1 and the hadronic \(\tau \) reconstruction is described in Sect. 5.3.2. The reconstructed hadronic \(\tau \) lepton is called \(\tau \) candidate in the following and denoted as \(\tau _{\mathrm{h }}\).
- 2.
Lepton, denoted as \(\ell \), stands for an electron or a muon only in the following.
- 3.
The Alpgen generator with CTEQ6L1 parton distribution function is used in the fully simulated signal samples throughout the whole analysis and also for the \(C_Z\) calculation. The reason why Alpgen is not used also for the \(A_{Z}\) calculation is a problem with the description of the \(Z\) boson rapidity when using the CTEQ6L1 PDF set. This problem is not expected to affect the reconstruction level description of event kinematics, but it could affect the extrapolation to the total cross section. Therefore it was decided to use Pythia with MRSTLO* for the \(A_{Z}\) calculation.
- 4.
The Alpgen generator is a tree-level matrix element calculator for a fixed number of partons. It gives a more precise description for processes with high jet multiplicities compared to generators where the additional jets are produced only during the shower evolution (e.g. Pythia). Furthermore, higher statistics has been available in Alpgen samples than in Pythia.
- 5.
The two components of the combined trigger used in the \(\tau _{e}\tau _{\mathrm{\,h }}\) channel (electron trigger and hadronic \(\tau \) trigger) are considered uncorrelated to each other and thus they are measured and applied separately.
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Novakova, J. (2014). \(Z \rightarrow \tau \tau \) Cross Section Measurement. In: Standard Model Measurements with the ATLAS Detector. Springer Theses. Springer, Cham. https://doi.org/10.1007/978-3-319-00810-3_5
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