Universally applicable kinematic cuts for the EVA description of diphoton production

Determine whether universally applicable experimental or theoretical kinematic cuts can be constructed that make the Equivalent Vector Boson Approximation reliably reproduce the full matrix-element calculation for $e^+\mu^- \to \gamma\gamma + \bar\nu_e\nu_\mu$ without relying on finely tuned, process-specific selections.

Background

The diphoton process receives substantial contributions from non-vector-boson-fusion topologies, especially bremsstrahlung-like photon emission from the initial-state leptons. Because the final-state particles are massless and the process lacks an inherent large scale, the EVA does not reproduce the full calculation over the general phase space.

The thesis explores several technical cuts, including invariant-mass, transverse-momentum, angular-separation, pseudorapidity, and pair-invariant-mass cuts. Although agreement can be improved in limited regions, the study reports that no generally applicable set of cuts was found.