Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at s=13 TeV with the ATLAS experiment

Journal article

A measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of √s = 13 TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb−1. The measurement is performed selecting tt¯ events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos θ ∗ variable, where θ ∗ is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos θ ∗ angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f0 = 0.684 ± 0.005 (stat.) ± 0.014 (syst.), fL = 0.318 ± 0.003 (stat.) ± 0.008 (syst.) and fR = −0.002 ± 0.002 (stat.) ± 0.014 (syst.), in agreement with the Standard Model prediction

Authors: Aad, G; Abbott, B; Abbott, DC; Abeling, K; Abidi, SH

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Physics Letters B
• Volume: 843
• Pages: 137829-137829
• Article number: 137829
• Publication date: 2023-06-05
• DOI: 10.1016/j.physletb.2023.137829
• EISSN: 1873-2445
• ISSN: 0370-2693
• Language: English
• Keywords: Nuclear physics; Standard Model (mathematical formulation); Physics; Top quark; Muon; Boson; Lepton; Luminosity; Electron; Higgs boson; Quark; Particle physics; Bottom quark