Measurement of the W boson polarisation in tt̄ events from pp collisions at √s=8 TeV in the lepton + jets channel with ATLAS

Allbrooke, B M M, Asquith, L, Cerri, A, Chavez Barajas, C A, De Santo, A, Salvatore, F, Santoyo Castillo, I, Suruliz, K, Sutton, M R, Vivarelli, I and The ATLAS Collaboration, (2017) Measurement of the W boson polarisation in tt̄ events from pp collisions at √s=8 TeV in the lepton + jets channel with ATLAS. European Physical Journal C, 77 (4). a264. ISSN 1434-6044

[img] PDF - Published Version
Available under License Creative Commons Attribution.

Download (2MB)

Abstract

This paper presents a measurement of the polarisation of W bosons from tt̄ decays, reconstructed in events with one high-pT lepton and at least four jets. Data from pp collisions at the LHC were collected at √s=8 TeV and correspond to an integrated luminosity of 20.2 fb −¹. The angle θ∗ between the b-quark from the top quark decay and a direct W boson decay product in the W boson rest frame is sensitive to the W boson polarisation. Two different W decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying W boson, respectively. The most precise measurement of the W boson polarisation via the distribution of cosθ∗ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as b-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are F0= 0.709 ± 0.019, FL= 0.299 ± 0.015 and FR=−0.008 ± 0.014, and are the most precisely measured W boson polarisation fractions to date. Limits on anomalous couplings of the Wtb vertex are set.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Experimental Particle Physics Research Group
Subjects: Q Science > QC Physics
Depositing User: Billy Wichaidit
Date Deposited: 24 Jul 2017 10:41
Last Modified: 24 Jul 2017 10:52
URI: http://sro.sussex.ac.uk/id/eprint/69413

View download statistics for this item

📧 Request an update
Project NameSussex Project NumberFunderFunder Ref
ATLASG0275STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/I006048/1