Next-to-Leading Order Gamma Gamma + 2-Jet Production at the LHC

TL;DR

This work delivers next-to-leading order QCD predictions for diphoton production in association with two jets at the LHC, focusing on backgrounds to Higgs-like processes in the vector-boson fusion channel. Using on-shell unitarity in BlackHat together with SHERPA, the authors compute Born, virtual, and real-emission contributions, incorporate Catani–Seymour subtraction, and adopt the Frixione photon isolation to avoid fragmentation uncertainties. They study multiple cut schemes (basic, ATLAS, CMS, with and without VBF) and demonstrate that NLO predictions reduce scale uncertainties to around 10–15% in many distributions, while pure-gluon contributions remain small but non-negligible in some regions. The analysis provides extensive cross sections and differential distributions, with publicly released $n$-tuples to facilitate experimental comparisons and future refinements of Higgs-background estimates in $oldsymbol{ ext{γγ+2 jets}}$ analyses.

Abstract

We present next-to-leading order QCD predictions for cross sections and for a comprehensive set of distributions in diphoton + 2-jet production at the Large Hadron Collider. We consider the contributions from loop amplitudes for two photons and four gluons, but we neglect top quarks. We use BlackHat together with SHERPA to carry out the computation. We use a Frixione cone isolation for the photons. We study standard sets of cuts on the jets and the photons, and also sets of cuts appropriate for studying backgrounds to Higgs-boson production via vector-boson fusion.

Figures (20)

• Figure 1: Examples of six-point loop diagrams for the processes $q g \rightarrow \gamma\gamma q g$ and $q \bar{q}' \rightarrow \gamma\gamma q\bar{q}'$.
• Figure 2: Examples of six-point fermion-loop diagrams for the processes $q g \rightarrow \gamma\gamma q g$ and $q \bar{q}' \rightarrow \gamma\gamma q\bar{q}'$. These diagrams have a closed quark loop, but the photons do not couple directly to it.
• Figure 3: Examples of six-point fermion-loop diagrams for the processes $q g \rightarrow \gamma\gamma q g$ and $q \bar{q}' \rightarrow \gamma\gamma q\bar{q}'$. These diagrams have a closed quark loop. In (a), one photon couples directly to the quark loop, whereas in (b) and (c), both photons couple to the quark loop.
• Figure 4: Example of a six-point one-loop diagram for the process $g g \rightarrow \gamma\gamma g g$. This one-loop amplitude is finite because the corresponding tree-level amplitude vanishes.
• Figure 5: Examples of seven-point real-emission diagrams for the processes $q g \rightarrow \gamma\gamma q ggg$ and $q \bar{q} \rightarrow \gamma\gamma q' \bar{q}' g$.