Model-Independent Measurement of the W-Boson Helicity in Top-Quark Decays at D0

Authors

V. M. Abazov, Joint Institute for Nuclear Research, Dubna, Russia
Kenneth A. Bloom, University of Nebraska-LincolnFollow
Gregory Snow, University of Nebraska-LincolnFollow
D0 Collaboration

Date of this Version

February 2008

Comments

Published by American Physical Society. Phys. Rev. Lett. 100, 062004 (2008). http://prl.aps.org. Copyright © 2008 American Physical Society. Permission to use.

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 tt events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron pp Collider. We reconstruct the angle Ө* 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 cosӨ* distribution finds that the fraction of longitudinal W bosons ƒ₀ = 0.425 ± 0.166(stat) ± 0.102(syst) and the fraction of right-handed W bosons ƒ₊ = 0.119 ± 0.090(stat) ± 0.053(syst), which is consistent at the 30% C.L. with the standard model.