Measurement of the W-boson helicity in top-quark decays from tt production in lepton+jets events in pp collisions at√s = 7 TeV

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Eroe, J. and Fabjan, C. and Friedl, M. and Fruhwirth, R. and Ghete, V. M. and Hormann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knunz, V. and Krammer, M. and Kratschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schofbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Molnár, József and Pálinkás, József and Karancsi, János and Trócsányi, Zoltán and Ujvári, Balázs and Krajczár, Krisztián and Veres, Gábor (2013) Measurement of the W-boson helicity in top-quark decays from tt production in lepton+jets events in pp collisions at√s = 7 TeV. JOURNAL OF HIGH ENERGY PHYSICS (10). ISSN 1126-6708

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Abstract

The W-boson helicity fractions in top-quark decays are measured with tt events in the lepton+jets final state, using proton-proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the CMS detector at the LHC. The data sample cor- responds to an integrated luminosity of 5.0 fb−1. The measured fractions of longi- tudinal, left-, and right-handed helicity are F0 = 0.682 ± 0.030 (stat.) ± 0.033 (syst.), FL = 0.310 ± 0.022 (stat.) ± 0.022 (syst.), and FR = 0.008 ± 0.012 (stat.) ± 0.014 (syst.), consistent with the standard model predictions. The measured fractions are used to probe the existence of anomalous Wtb couplings. Exclusion limits on the real compo- nents of the anomalous couplings gL, gR are also derived.

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