Measurement of $\tau $ polarisation in $Z/\gamma ^{*}\rightarrow \tau \tau $ decays in proton–proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat; Abeloos, Baptiste; Abidi, Syed Haider; AbouZeid, Ossama; Abraham, Nicola; Abramowicz, Halina; Abreu, Henso

doi:10.1140/epjc/s10052-018-5619-1

Measurement of $\tau$ polarisation in $Z/\gamma ^{*}\rightarrow \tau \tau$ decays in proton–proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

ATLAS

Collaboration

Sep 11, 2017

44 pages

Published in:

Eur.Phys.J.C 78 (2018) 2, 163

Published: Feb 24, 2018

e-Print:

1709.03490 [hep-ex]

DOI:

10.1140/epjc/s10052-018-5619-1

Report number:

CERN-EP-2017-172

Experiments:

CERN-LHC-ATLAS

View in:

datasets

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Abstract: (Springer)

This paper presents a measurement of the polarisation of

\tau

leptons produced in

Z/\gamma ^{*}\rightarrow \tau \tau

decays which is performed with a dataset of proton—proton collisions at

\sqrt{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/\gamma ^{*}\rightarrow \tau \tau

decays are reconstructed from a hadronically decaying

\tau

lepton with a single charged particle in the final state, accompanied by a

\tau

lepton that decays leptonically. The

\tau

polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic

\tau

decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The

\tau

polarisation extracted over the full phase space within the

Z/\gamma ^{*}

mass range of 66

< m_{Z/\gamma ^{*}} <

116 GeV is found to be

P_{\tau } =-0.14 \pm 0.02 (\text {stat}) \pm 0.04 (\text {syst})

. It is in agreement with the Standard Model prediction of

P_{\tau } =-0.1517 \pm 0.0019

, which is obtained from the ALPGEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA

\tau

decay library.

Note:

44 pages in total, author list starting page 28, 6 figures, 7 tables, submitted to EPJC. Al l figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2015-18

p p: scattering
p p: colliding beams
Z0: leptonic decay
tau: pair production
tau: hadronic decay
tau: leptonic decay
tau: polarization: measured
parton: showers
ATLAS
charged particle

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