Abstract
We define three orthogonal axes to investigate the top quark polarization in the $t$-channel single top process. We provide expressions for the polarization in these axes in terms of anomalous $Wtb$ couplings. It is found that the polarizations in the two axes orthogonal to the spectator quark axis are very sensitive to an anomalous coupling involving a $\bar b_L \sigma^{\mu \nu} t_R$ dipole term. In particular, an asymmetry based on the polarization normal to the production plane is more sensitive to the imaginary part of this coupling than previously studied observables.
Highlights
Single top-quark production at hadron colliders is at present the only source of polarized top quarks
It is found that the polarizations in the two axes orthogonal to the spectator quark axis are very sensitive to an anomalous coupling involving a b LσμνtR dipole term
In this paper we study the top-quark polarization in the t-channel process in the spectator quark direction and in two orthogonal axes, providing a complete description of the top-(anti)quark polarization
Summary
Single top-quark production at hadron colliders is at present the only source of polarized top quarks. For the t-channel process, it is well known that, both at the Fermilab Tevatron [1] and the CERN LHC [2], top quarks are produced with a high polarization in the direction of the spectator quark in the top-quark rest frame. We give for the first time expressions for the polarizations in these axes for a general Wtb effective vertex with anomalous couplings. The sensitivity to these nonstandard contributions is estimated. Previous work [4] investigated the polarization in the spectator quark and helicity axes and their dependence on one of the three possible anomalous Wtb couplings
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