Measurement of the W boson polarisation in t\bar{t} events from pp collisions at √{s} = 8 TeV in the lepton + jets channel with ATLAS
Abstract
This paper presents a measurement of the polarisation of W bosons from t\bar{t} decays, reconstructed in events with one high-p_{{ T }} 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 cos {θ ^{*}} 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.
- Publication:
-
European Physical Journal C
- Pub Date:
- April 2017
- DOI:
- 10.1140/epjc/s10052-017-4819-4
- arXiv:
- arXiv:1612.02577
- Bibcode:
- 2017EPJC...77..264A
- Keywords:
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- High Energy Physics - Experiment
- E-Print:
- 42 pages in total, author list starting page 26, 6 figures, 5 tables, published in EPJC. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2016-02. v3 includes modifications described in the erratum that can be found at https://link.springer.com/article/10.1140%2Fepjc%2Fs10052-018-6520-7