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
Creators: name: Aad, G
name: Abbott, B
name: Abbott, DC
name: Abed Abud, A
name: Abeling, K
name: Abhayasinghe, DK
name: Abidi, SH
name: Abramowicz, H
name: Abreu, H
name: Abulaiti, Y
name: Abusleme Hoffman, AC
name: Acharya, BS
name: Achkar, B
name: Adam, L
name: Adam Bourdarios, C
name: Adamczyk, L
name: Adamek, L
name: Addepalli, SV
name: Adelman, J
name: Adiguzel, A
name: Adorni, S
name: Adye, T
name: Affolder, AA
name: Afik, Y
name: Agapopoulou, C
name: Agaras, MN
name: Agarwala, J
name: Aggarwal, A
name: Agheorghiesei, C
name: Aguilar-Saavedra, JA
name: Ahmad, A
name: Ahmadov, F
name: Ahmed, WS
name: Ai, X
name: Aielli, G
name: Aizenberg, I
name: Akatsuka, S
name: Akbiyik, M
name: Åkesson, TPA
name: Akimov, AV
name: Al Khoury, K
name: Alberghi, GL
name: Albert, J
name: Albicocco, P
name: Alconada Verzini, MJ
name: Alderweireldt, S
name: Aleksa, M
name: Aleksandrov, IN
name: Alexa, C
name: Alexopoulos, T
name: Alfonsi, A
name: Alfonsi, F
name: Alhroob, M
name: Ali, B
name: Ali, S
name: Aliev, M
name: Alimonti, G
name: Allaire, C
name: Allbrooke, BMM
name: Allport, PP
name: Aloisio, A
name: Alonso, F
name: Alpigiani, C
name: Alunno Camelia, E
name: Alvarez Estevez, M
name: Alviggi, MG
name: Amaral Coutinho, Y
name: Ambler, A
name: Ambroz, L
name: Amelung, C
name: Amidei, D
name: Amor Dos Santos, SP
name: Amoroso, S
name: Amrouche, CS
name: Anastopoulos, C
name: Andari, N
name: Andeen, T
name: Anders, JK
name: Andrean, SY
name: Andreazza, A
name: Angelidakis, S
name: Angerami, A
name: Anisenkov, AV
name: Annovi, A
name: Antel, C
name: Anthony, MT
name: Antipov, E
name: Antonelli, M
name: Antrim, DJA
name: Anulli, F
name: Aoki, M
name: Aparisi Pozo, JA
name: Aparo, MA
name: Aperio Bella, L
name: Aranzabal, N
name: Araujo Ferraz, V
name: Arcangeletti, C
name: Arce, ATH
name: Arena, E
name: Arguin, JF
Publisher: name: Apollo - University of Cambridge Repository
Year: 2022
Subjects: Regular Article - Experimental Physics
Hadron-Hadron Scattering
Top Physics

description: 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<sup>−1</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 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 $$ {P}_{x^{\prime }} $$ P x ′ = 0.01 ± 0.18, $$ {P}_{y^{\prime }} $$ P y ′ = −0.029 ± 0.027, $$ {P}_{z^{\prime }} $$ P z ′ = 0.91 ± 0.10 and for the top-antiquark event sample they are $$ {P}_{x^{\prime }} $$ P x ′ = −0.02 ± 0.20, $$ {P}_{y^{\prime }} $$ P y ′ = −0.007 ± 0.051, $$ {P}_{z^{\prime }} $$ P z ′ = 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 $$ \mathcal{O} $$ O <sub>tW</sub> operator in the framework of an effective field theory. The obtained bounds are C<sub>tW</sub> ∈ [−0.9, 1.4] and C<sub>itW</sub> ∈ [−0.8, 0.2], both at 95% confidence level.