Abstract
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 tt̅ 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 cosθ∗ 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 cosθ∗ 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.
Original language | English |
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Article number | 137829 |
Journal | Physics Letters B |
Early online date | 5 Jun 2023 |
DOIs | |
Publication status | E-pub ahead of print - 5 Jun 2023 |
Bibliographical note
21 pages in total, 3 figures, 2 tables, submitted to PLB. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2018-28/Keywords
- hep-ex