Measurement of the polarisation of single top quarks and antiquarks produced in the t-channel at √s=13 TeV and bounds on the tWb dipole operator from the ATLAS experiment



Aad, G, Abbott, B, Abbott, DC, Abud, A Abed, Abeling, K, Abhayasinghe, DK, Abidi, SH, Abramowicz, H, Abreu, H, Abulaiti, Y
et al (show 2877 more authors) (2022) Measurement of the polarisation of single top quarks and antiquarks produced in the t-channel at √s=13 TeV and bounds on the tWb dipole operator from the ATLAS experiment JOURNAL OF HIGH ENERGY PHYSICS, 2022 (11). 40-. ISSN 1126-6708, 1029-8479

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Abstract

A simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in t-channel single-top-quark production is presented. This analysis is based on data from proton–proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb−1, collected with the ATLAS detector at the LHC. Selected events contain exactly one isolated electron or muon, large missing transverse momentum and exactly two jets, one being b-tagged. Stringent selection requirements are applied to discriminate t-channel single-top-quark events from the background contributions. The top-quark and top-antiquark polarisation vectors are measured from the distributions of the direction cosines of the charged-lepton momentum in the top-quark rest frame. The three components of the polarisation vector for the selected top-quark event sample are Px′ = 0.01 ± 0.18, Py′ = −0.029 ± 0.027, Pz′ = 0.91 ± 0.10 and for the top-antiquark event sample they are Px′ = −0.02 ± 0.20, Py′ = −0.007 ± 0.051, Pz′ = 0.79 ± 0.16. Normalised differential cross-sections corrected to a fiducial region at the stable-particle level are presented as a function of the charged-lepton angles for top-quark and top-antiquark events inclusively and separately. These measurements are in agreement with Standard Model predictions. The angular differential cross-sections are used to derive bounds on the complex Wilson coefficient of the dimension-six O<inf>tW</inf> operator in the framework of an effective field theory. The obtained bounds are C<inf>tW</inf> ∈ [−0.9, 1.4] and C<inf>itW</inf> ∈ [−0.8, 0.2], both at 95% confidence level. [Figure not available: see fulltext.].

Item Type: Article
Uncontrolled Keywords: Hadron-Hadron Scattering, Top Physics
Depositing User: Symplectic Admin
Date Deposited: 14 Dec 2022 11:51
Last Modified: 22 May 2026 15:21
DOI: 10.1007/JHEP11(2022)040
Open Access URL: https://doi.org/10.1007/JHEP11(2022)040
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3166651
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