Measurement of the polarisation of single top quarks and antiquarks produced in the <i>t</i>-channel at √<i>s</i>=13 TeV and bounds on the <i>tWb</i> 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 <i>t</i>-channel at √<i>s</i>=13 TeV and bounds on the <i>tWb</i> dipole operator from the ATLAS experiment. JOURNAL OF HIGH ENERGY PHYSICS, 2022 (11). 40-.

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Abstract

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>A simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in <jats:italic>t</jats:italic>-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<jats:sup><jats:italic>−</jats:italic>1</jats:sup>, 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 <jats:italic>b</jats:italic>-tagged. Stringent selection requirements are applied to discriminate <jats:italic>t</jats:italic>-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 <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {P}_{x^{\prime }} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:msup> <mml:mi>x</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> = 0<jats:italic>.</jats:italic>01 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>18, <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {P}_{y^{\prime }} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:msup> <mml:mi>y</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> = <jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>029 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>027, <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {P}_{z^{\prime }} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:msup> <mml:mi>z</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> = 0<jats:italic>.</jats:italic>91 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>10 and for the top-antiquark event sample they are <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {P}_{x^{\prime }} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:msup> <mml:mi>x</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> = <jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>02 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>20, <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {P}_{y^{\prime }} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:msup> <mml:mi>y</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> = <jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>007 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>051, <jats:inline-formula><jats:alternatives><jats:tex-math>$$ {P}_{z^{\prime }} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>P</mml:mi> <mml:msup> <mml:mi>z</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> = 0<jats:italic>.</jats:italic>79 <jats:italic>±</jats:italic> 0<jats:italic>.</jats:italic>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 <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \mathcal{O} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>O</mml:mi> </mml:math></jats:alternatives></jats:inline-formula><jats:sub><jats:italic>tW</jats:italic></jats:sub> operator in the framework of an effective field theory. The obtained bounds are <jats:italic>C</jats:italic><jats:sub><jats:italic>tW</jats:italic></jats:sub> ∈ [<jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>9<jats:italic>,</jats:italic> 1<jats:italic>.</jats:italic>4] and <jats:italic>C</jats:italic><jats:sub><jats:italic>itW</jats:italic></jats:sub> ∈ [<jats:italic>−</jats:italic>0<jats:italic>.</jats:italic>8<jats:italic>,</jats:italic> 0<jats:italic>.</jats:italic>2], both at 95% confidence level.</jats:p>

Item Type: Article
Uncontrolled Keywords: Hadron-Hadron Scattering, Top Physics
Depositing User: Symplectic Admin
Date Deposited: 14 Dec 2022 11:51
Last Modified: 18 Mar 2024 04:02
DOI: 10.1007/JHEP11(2022)040
Open Access URL: https://doi.org/10.1007/JHEP11(2022)040
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3166651