Model-independent measurement of the W boson helicity in top quark decays

Abstract

We present the first model-independent measurement of the helicity of $W$ bosons produced in top quark decays, based on a 1 fb${}^{-1}$ sample of candidate $t\bar{t}$ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. We reconstruct the angle ${\theta }^{\ast }$ between the momenta of the down-type fermion and the top quark in the $W$ boson rest frame for each top quark decay. A fit of the resulting \costheta distribution finds that the fraction of longitudinal $W$ bosons $f_0=0.425\pm 0.166(stat.)\pm 0.102(syst.)$ and the fraction of right-handed $W$ bosons $f_{+}=0.119\pm 0.090(stat.)\pm 0.053(syst.)$, which is consistent at the 30% C.L. with the standard model.

arXiv commentsubmitted to Phys. Rev. Lett

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