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Scientific article
Open access
English

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

ContributorsATLAS Collaboration
Published inEuropean physical journal. C, Particles and fields, vol. 77, no. 4, 264
Collection
  • Open Access - SCOAP3
Publication date2017
Abstract

This paper presents a measurement of the polarisation of W bosons from tt¯ 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.

Citation (ISO format)
ATLAS Collaboration. Measurement of the W boson polarisation in tt¯ events from pp collisions at √s = 8 TeV in the lepton + jets channel with ATLAS. In: European physical journal. C, Particles and fields, 2017, vol. 77, n° 4, p. 264. doi: 10.1140/epjc/s10052-017-4819-4
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Article (Published version)
Identifiers
ISSN of the journal1434-6044
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