Spin effects in the antler event topology at hadron colliders

TL;DR

This paper analyzes spin correlation effects in the antler event topology at the LHC, deriving analytical expressions for various kinematic variables to aid in spin discrimination.

Contribution

It provides the first analytical derivation of differential distributions for spin correlations in the antler topology at threshold and infinity, including problematic cases.

Findings

Analytical expressions for cosθ_{ll}^* distributions at threshold and high energy.

Identification of cases where spin discrimination is challenging.

Insights into how spin correlations affect kinematic variable shapes.

Abstract

We investigate spin correlation effects in the "antler" event topology pp-> A-> B1, B2 -> l^{-}, C1, 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 M_{ll}, Meff, \sqrt{s}_{min}, MT2, MCT and MCTx. We focus on the two kinematic extremes of \sqrt{s} - threshold and infinity - and derive analytical expressions for the differential distributions of several variables, most notably the cos{\theta_{ll}}^* variable proposed by Barr in hep-ph/0511115. For all possible spin assignments of particles A, B and C, we derive the cos{\theta_{ll}}^* differential distribution at threshold, including the effects of spin correlations. Our analytical results help identify the problematic cases for spin discrimination.