Measurement of the ? lepton polarization in Z boson decays in proton-proton collisions at (Formula presented.)

Abstract

The polarization of ? leptons is measured using leptonic and hadronic ? lepton decays in Z ? ?+ ?? events in proton-proton collisions at (Formula presented.) recorded by CMS at the CERN LHC with an integrated luminosity of 36.3 fb?1. The measured ?? lepton polarization at the Z boson mass pole is P?(Z) = ?0.144 � 0.006 (stat) � 0.014 (syst) = ?0.144 � 0.015, in good agreement with the measurement of the ? lepton asymmetry parameter of A? = 0.1439 � 0.0043 = ? P?(Z) at LEP. The ? lepton polarization depends on the ratio of the vector to axial-vector couplings of the ? leptons in the neutral current expression, and thus on the effective weak mixing angle sin2 ?Weff , independently of the Z boson production mechanism. The obtained value sin2 ?Weff = 0.2319 � 0.0008(stat) � 0.0018(syst) = 0.2319 � 0.0019 is in good agreement with measurements at e+ e? colliders. [Figure not available: see fulltext.]. � 2024, The Author(s).