CMS-PAS-SMP-18-010

CMS-PAS-SMP-18-010
Measurement of the $\tau$ lepton polarization in Z boson decays
CMS Collaboration
10 February 2023

Abstract: The polarization of $\tau$ leptons is measured using leptonic and hadronic $\tau$ lepton decays in $\mathrm{Z}\rightarrow\tau\tau$ events. A sample of pp collisions of an integrated luminosity of 36.3 fb $^{-1}$ at $\sqrt{s}=$ 13 TeV is used. The measured polarization at the Z pole is $\mathcal{P}_{\tau}(\mathrm{Z}) = -$ 0.144 $\pm$ 0.015 $= -$ 0.144 $\pm$ 0.006 (stat) $\pm$ 0.014 (syst), in good agreement with the standard model value of the lepton asymmetry parameter of $A_{\ell} =$ 0.1468 $\pm$ 0.0003. The $\tau$ polarization is used to determine the ratio of the vector to axial-vector coupling of the $\tau$ leptons in the neutral current and thus the weak mixing angle independently of the production process of the Z resonance. The obtained value is $\sin^2\theta^{\mathrm{eff}}_W =$ 0.2319 $\pm$ 0.0019 $=$ 0.2319 $\pm$ 0.0008 (stat) $\pm$ 0.0018 (syst).
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here.

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