γγγγ production at the LHC: An application of 2 →4 analytic unitarity

We present next-to-leading order (NLO) predictions for γγγγ final states, including the effects of photon fragmentation. Our results are calculated fully analytically using the techniques of D-dimensional unitarity, and we discuss some refinements to existing methods, focusing particularly on the role of three-mass triangle coefficients. Using these techniques we are able to produce a numerically stable Monte Carlo code that runs fully in double precision. We investigate the 4γ signal at colliders, both for Run II of the LHC and at future machines. Our results are implemented in MCFM.