Measurement of the $\tau$ lepton polarization in Z boson decays in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

The polarization of $\tau$ leptons is measured using leptonic and hadronic $\tau$ lepton decays in Z $\to$ ${\tau }^{+}{\tau }^{-}$ events in proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by CMS at the CERN LHC with an integrated luminosity of 36.3 fb${}^{-1}$. The measured ${\tau }^{-}$ polarization at the Z boson mass pole is ${\mathcal{P}}_{\tau }$(Z) = $-$0.144 $\pm$ 0.006 (stat) $\pm$ 0.014 (syst) = $-$0.144 $\pm$ 0.015, in good agreement with the measurement of the $\tau$ lepton asymmetry parameter of $A_{\tau }$ = 0.1439 $\pm$ 0.0043 = $-{\mathcal{P}}_{\tau }$(Z) at LEP. The $\tau$ polarization depends on the ratio of the vector to axial-vector couplings of the $\tau$ leptons in the neutral current expression, and thus on the effective weak mixing angle ${\sin }^2{\theta }_{\mathrm{W}}^{\text{eff}}$, independently of the Z boson production mechanism. The obtained value ${\sin }^2{\theta }_{\mathrm{W}}^{\text{eff}}$ = 0.2319 $\pm$ 0.0008 (stat) $\pm$ 0.0018 (syst) = 0.2319 $\pm$ 0.0019 is in good agreement with measurements at e${}^{+}$e${}^{-}$ colliders.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/SMP-18-010 (CMS Public Pages)

References in corpus (5)

• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• An Introduction to PYTHIA 8.2
• Single-top Wt-channel production matched with parton showers using the POWHEG method
• Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
• Pileup Per Particle Identification

Cited by in corpus (3)

• Strategy to measure tau $g-2$ via photon fusion in LHC proton collisions
• High-level hadronic tau lepton triggers of the CMS experiment in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV
• Towards a test of the Born rule in high-energy collisions