Measurement of tau polarisation in Z/gamma* -> tau tau decays in proton-proton collisions at root s=8 TeV with the ATLAS detector

M. Aaboud, G. Aad, B. Abbott, O. Abdinov, B Abeloos, S.H. Abidi, Ossama Sherif Alexander Abouzeid, NL Abraham, H. Abramowicz, H. Abreu, R. Abreu, Y. Abulaiti, B.S. Acharya, Shin-ichi Adachi, L. Adamczyk, J. Adelman, M. Adersberger, T. Adye, A. A. Affolder, Y. AfikT. Agatonovic-Jovin, S. P. Ahlen, Peter Henrik Hansen, Stefania Xella, James William Monk, Mogens Dam, Fabian Alexander Jürgen Thiele, Troels Christian Petersen, Jørn Dines Hansen, Geert-Jan Besjes, Simon Holm Stark, Gorm Aske Gram Krohn Galster, Alejandro Alonso Diaz, Graig Wiglesworth, Flavia de Almeida Dias, Jørgen Beck Hansen, Milena Bajic

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Abstract

This paper presents a measurement of the polarisation of τ leptons produced in Z/ γ→ ττ decays which is performed with a dataset of proton—proton collisions at s=8 TeV, corresponding to an integrated luminosity of 20.2 fb- 1 recorded with the ATLAS detector at the LHC in 2012. The Z/ γ→ ττ decays are reconstructed from a hadronically decaying τ lepton with a single charged particle in the final state, accompanied by a τ lepton that decays leptonically. The τ polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic τ decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The τ polarisation extracted over the full phase space within the Z/ γ mass range of 66 <mZ/ 116 GeV is found to be Pτ= - 0.14 ± 0.02 (stat) ± 0.04 (syst). It is in agreement with the Standard Model prediction of Pτ= - 0.1517 ± 0.0019 , which is obtained from the ALPGEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA τ decay library.

Original languageEnglish
Article number163
JournalEuropean Physical Journal C
Volume78
Issue number2
Number of pages30
ISSN1434-6044
DOIs
Publication statusPublished - 1 Feb 2018

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