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

CollaborationWith : Ancu, Lucian Stefan / Bilbao De Mendizabal, Javier / Calace, Noemi / Chatterjee, Avishek / Clark, Allan Geoffrey / Coccaro, Andrea / Delitzsch, Chris Malena / Della Volpe, Domenico / Ferrere, Didier / Golling, Tobias / Gonzalez Sevilla, Sergio / Gramling, Johanna Léna / Guescini, Francesco / Iacobucci, Giuseppe / Katre, Akshay / Khoo, Teng Jian / Lanfermann, Marie Christine / Lionti, Anthony Eric / March Ruiz, Luis / Mermod, Philippe / Nackenhorst, Olaf / Paolozzi, Lorenzo / Ristic, Branislav / Schramm, Steven / Sfyrla, Anna / Wu, Xin
Published in European Physical Journal. C. 2017, vol. 77, no. 4, p. 264
Collection Open Access - SCOAP3
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.
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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, 2017, vol. 77, n° 4, p. 264. https://archive-ouverte.unige.ch/unige:93916

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Deposited on : 2017-05-02

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