Spin effects in the antler event topology at hadron colliders

We investigate spin correlation effects in the "antler" event topology pp →A(A*) → B₁B₂ → (l-C ₁)(l+C₂) at the LHC. We study the shapes of several kinematic variables, including the relative pseudorapidity, relative azimuthal angle and the energies of the two leptons, as well as several mass variables Mll, Meff , √smin, MT2, MCT and MCTx. We focus on the two kinematic extremes of √s - threshold and infinity - and derive analytical expressions for the differential distributions of several variables, most notably the cos θ* _l-l+ variable proposed by Barr in hep-ph/0511115. For all possible spin assignments of particles A, B and C, we derive the cos θ* _l-l+ differential distribution at threshold, including the effects of spin correlations. Our analytical results help identify the problematic cases for spin discrimination.