Measurement of the W boson helicity fractions in the decays of top quark pairs to lepton plus jets final states produced in pp collisions at root s=8 TeV

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Khachatryan, V.
Sirunyan, A. M.
Tumasyan, A.
Adam, W.
Asilar, E.
Bergauer, T.
Brandstetter, J.
Brondolin, E.
Dragicevic, M.
Eroe, J.
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Elsevier B.V.
The W boson helicity fractions from top quark decays in t (t) over bar events are measured using data from proton-proton collisions at a centre-of-mass energy of 8 TeV. The data were collected in 2012 with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.8 fb(-1). Events are reconstructed with either one muon or one electron, along with four jets in the final state, with two of the jets being identified as originating from b quarks. The measured helicity fractions from both channels are combined, yielding F-0 = 0.681 +/- 0.012 (stat) +/- 0.023 (syst), F-L = 0.323 +/- 0.008 (stat) +/- 0.014 (syst), and F-R = -0.004 +/- 0.005 (stat) +/- 0.014 (syst) for the longitudinal, left-, and right-handed components of the helicity, respectively. These measurements of the W boson helicity fractions are the most accurate to date and they agree with the predictions from the standard model. (C) 2016 The Author. Published by Elsevier B.V.
CMS, Physics, Top, Anomalous couplings, Helicity
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Physics Letters B. Amsterdam: Elsevier Science Bv, v. 762, p. 512-534, 2016.