Azimuthal correlation between the $(\vec{p}_l,\vec{p}_{X_b})$ and   $(\vec{p}_l,\vec{P}_t)$ planes in the semileptonic rest frame decay of a   polarized top quark: An $O(\alpha_s)$ effect
  The azimuthal correlation between the planes formed by the vectors   $(\vec{p}_\ell,\vec{p}_{X_b})$ and $(\vec{p}_\ell,\vec{P}_t)$ in the semileptonic rest frame decay of a polarized top quark $t(\uparrow) \to X_b + l^+ + \nu_\ell$ belongs to a class of polarization observables involving the top quark which vanish at the Born term level in the standard model. We determine the next--to--leading order QCD corrections to the afore-mentioned azimuthal correlation and compare the result to the corresponding contribution of a non--standard--model right--chiral quark current. 
S. Groote, W.S. Huo, A. Kadeer, J. G. Korner