Triphoton production at hadron colliders

TL;DR

This work delivers NLO predictions for triphoton production at the LHC and Tevatron, explicitly incorporating photon fragmentation and comparing fixed-energy, fractional, and smooth cone isolation schemes. It provides compact analytic one-loop amplitudes for γγγ and γγ+jet derived via analytic unitarity and integrates them into the MCFM framework. The study finds that smooth cone and fractional isolations agree reasonably when fragmentation is constrained to LO accuracy, but higher-order fragmentation corrections can cause notable differences, underscoring sensitivity to fragmentation inputs. Phenomenologically, triphoton cross sections at the LHC are of order a few fb with large NLO K-factors (~2) and manageable scale uncertainties, while Tevatron predictions suggest a reachable event yield, making this triboson channel a useful probe of electroweak–QCD dynamics and isolation effects.

Abstract

We present next-to-leading order predictions for the production of triphoton final states at the LHC and the Tevatron. Our results include the effect of photon fragmentation for the first time and we are able to quantify the impact of different isolation prescriptions. We find that calculations accounting for fragmentation effects at leading order, and those employing a smooth cone isolation where no fragmentation contribution is required, are in reasonable agreement with one another. However, larger differences in the predicted rates arise when higher order corrections to the fragmentation functions are included. In addition we present full analytic results for the $γγγ$ and $γγ+$jet one-loop amplitudes. These amplitudes, which are particularly compact, may be useful to future higher-order calculations. Our results are available in the Monte Carlo code MCFM.

Figures (4)

• Figure 1: Dependence of the NLO triphoton cross section on the parameter that controls the amount of hadronic energy inside the isolation cone, $\epsilon_\gamma$. Results are shown for the fractional and smooth cone isolation procedures, using an isolation cone of size $R_0=0.4$ (left) and $R_0=0.7$ (right). Smooth cone predictions correspond to the dashed line, while the solid line represents the LO GdRG prediction and the dotted lines correspond to the BFG (magenta) and NLO GdRG (red) fragmentation sets.
• Figure 2: Dependence of the NLO triphoton cross section on the parameter that controls the amount of hadronic energy inside the isolation cone, $\epsilon_\gamma$ with harder selection requirements $p_T^{\gamma} > 50$ GeV, and staggered cuts $p_T^{\gamma} > 100, 50, 30$ GeV. Results are shown for the fractional and smooth cone isolation procedures, using an isolation cone of size $R_0=0.4$ (left) and $R_0=0.7$ (right).
• Figure 3: Dependence of the NLO $\gamma\gamma+$jet cross section on the parameter that controls the amount of hadronic energy inside the isolation cone, $\epsilon_\gamma$. Results are shown for the fractional and smooth cone isolation procedures, using an isolation cone of size $R_0=0.4$ (left) and $R_0=0.7$ (right).
• Figure 4: The $p_{T,\gamma}$ spectrum for the hardest photon at the 8 TeV LHC. The solid lines represent the contributions with $\mu=m_{\gamma\gamma\gamma}$, the dashed lines represent the NLO predictions with $\mu=\{0.5,2\} m_{\gamma\gamma\gamma}$.