On measurement of top polarization as a probe of $t \bar t$ production mechanisms at the LHC

Understand

In this note we demonstrate the use of top polarization in the study of $t \bar t$ resonances at the LHC, in the possible case where the dynamics implies a non-zero top polarization.

• As a probe of top polarization we construct an asymmetry in the decay-lepton azimuthal angle distribution (corresponding to the sign of $\cos\phi_\ell$) in the laboratory.
• The asymmetry is non-vanishing even for a symmetric collider like the LHC, where a positive $z$ axis is not uniquely defined.
• The angular distribution of the leptons has the advantage of being a faithful top-spin analyzer, unaffected by possible anomalous $tbW$ couplings, to linear order.