  Top-antitop pairs produced in the decay of a new heavy resonance will exhibit
spin correlations that contain valuable coupling information. When the tops
decay, these correlations imprint themselves on the angular patterns of the
final quarks and leptons. While many approaches to the measurement of top spin
correlations are known, the most common ones require detailed kinematic
reconstructions and are insensitive to some important spin interference
effects. In particular, spin-1 resonances with mostly-vector or mostly-axial
couplings to top cannot be easily discriminated from one another without
appealing to mass-suppressed effects or to more model-dependent interference
with continuum Standard Model production. Here, we propose to probe the
structure of a resonance's couplings to tops by measuring the azimuthal angles
of the tops' decay products about the production axis. These angles exhibit
modulations which are typically O(0.1-1), and which by themselves allow for
discrimination of spin-0 from higher spins, measurement of the CP-phase for
spin-0, and measurement of the vector/axial composition for spins 1 and 2. For
relativistic tops, the azimuthal decay angles can be well-approximated without
detailed knowledge of the tops' velocities, and appear to be robust against
imperfect energy measurements and neutrino reconstructions. We illustrate this
point in the highly challenging dileptonic decay mode, which also exhibits the
largest modulations. We comment on the relevance of these observables for
testing axigluon-like models that explain the top quark A_FB anomaly at the
Tevatron, through direct production at the LHC.
