Wuppertal 2015 – scientific programme

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T: Fachverband Teilchenphysik

T 65: Top: Spin, Winkelverteilungen, Asymmetrie, Breite

T 65.2: Talk

Wednesday, March 11, 2015, 17:00–17:15, L.10.31 (HS 10)

Measurement of the W-Boson Helicity fractions in tt Events at √s=8 TeV in the Lepton+Jets Channel with ATLAS — •Mohammad Jawad Kareem, Boris Lemmer, Arnulf Quadt, and Elizaveta Shabalina — II. Physikalisches Institut, Georg-August-Universität Göttingen

A summary of the ongoing measurement of the W-boson helicity fractions in tt decays is presented. Events produced via pp collisions at a centre-of-mass energy of 8 TeV, collected in 2012 by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 20.3 fb⁻¹ have been analysed. The measurement is performed in the lepton+jets channel characterized by one isolated electron or muon, missing transverse momentum and at least four energetic jets of which at least two are tagged as a b-jet.

Using the kinematic likelihood fitter KLFitter, for the reconstruction of the top quarks, the angular distribution of the charged lepton (down type quark) in the leptonically (hadronically) decaying W-boson rest frame is sensitive to the three possible helicity states. The fractions are obtained by performing a template fit to data. As the polarization of the W-bosons in top quark decays is sensitive to the Wtb vertex structure, limits on anomalous Wtb couplings can be set.