Measurement of the W boson polarization in top decay at CDF at sqrt(s)=1.8 TeV

Authors

Darin Acosta, University of FloridaFollow
Kenneth A. Bloom, University of Nebraska-LincolnFollow
Collider Detector at Fermilab Collaboration

Document Type

Article

Date of this Version

2-25-2005

Comments

Published by American Physical Society. Phys. Rev. D 71, 031101 (2005). http://prd.aps.org/. Copyright © 2005 American Physical Society. Permission to use.

Abstract

The polarization of the W boson in t→Wb decay is unambiguously predicted by the standard model of electroweak interactions and is a powerful test of our understanding of the tWb vertex. We measure this polarization from the invariant mass of the b quark from t→Wb and the lepton from W→lν whose momenta measure the W decay angle and direction of motion, respectively. In this paper we present a measurement of the decay rate (f_v+A) of the W produced from the decay of the top quark in the hypothesis of V+A structure of the tWb vertex. We find no evidence for the nonstandard V+A vertex and set a limit on f_v+A < 0.80 at 95% confidence level. By combining this result with a complementary observable in the same data, we assign a limit on f_v+A < 0.61 at 95% CL. This corresponds to a constraint on the right-handed helicity component of the W polarization of f₊f_v+A in top decay.