# Measurement of the Helicity Fractions of W Bosons from Top Quark Decays Using Fully Reconstructed $t\bart$ Events with CDF II

Abstract : We present a measurement of the fractions F_0 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 318 pb -1. We select ttbar candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle theta*, 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 cos(theta*) distribution in the data is determined by full kinematic reconstruction of the ttbar candidates. We find F_0 = 0.85 +0.15 -0.22 (stat) +- 0.06 (syst) and F_+ = 0.05 +0.11 -0.05 (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.
Document type :
Journal articles

http://hal.in2p3.fr/in2p3-00147195
Contributor : Dominique Girod <>
Submitted on : Wednesday, May 16, 2007 - 10:32:13 AM
Last modification on : Wednesday, May 27, 2020 - 7:20:03 PM

### Citation

A. Abulencia, J. Adelman, T. Affolder, T. Akimoto, M. G. Albrow, et al.. Measurement of the Helicity Fractions of W Bosons from Top Quark Decays Using Fully Reconstructed $t\bart$ Events with CDF II. Physical Review D, American Physical Society, 2007, 75, pp.052001. ⟨10.1103/PhysRevD.75.052001⟩. ⟨in2p3-00147195⟩

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