Measurement of the helicity fractions of W bosons from top quark decays using fully reconstructed tt¯ events with CDF II

A. Abulencia et al. (CDF Collaboration)
Phys. Rev. D 75, 052001 – Published 15 March 2007

Abstract

We present a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top-quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318pb1. We select tt¯ candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle θ*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top-quark rest frame. The cosθ* distribution in the data is determined by full kinematic reconstruction of the tt¯ candidates. We find F0=0.850.22+0.15(stat)±0.06(syst) and F+=0.050.05+0.11(stat)±0.03(syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F+<0.26 at the 95% confidence level.

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  • Received 8 December 2006

DOI:https://doi.org/10.1103/PhysRevD.75.052001

©2007 American Physical Society

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Vol. 75, Iss. 5 — 1 March 2007

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