Wγγproduction with leptonic decays at NLO QCD

TL;DR

Precise SM predictions for W γ γ production with leptonic W decays are needed to probe triple and quartic gauge couplings and to quantify backgrounds for new physics. The authors compute ${\cal O}(\alpha_s)$ QCD corrections using Catani-Seymour subtraction, implement the process in the VBFNLO framework with full leptonic decays and Frixione photon isolation, and perform detailed scale variation and differential distribution studies. They find large corrections ($K \approx 3$ at the LHC, smaller at the Tevatron) that reshape spectra and spoil the LO radiation zero; jet vetoes partially mitigate some uncertainties but do not erase the need for NLO accuracy. These results underscore the necessity of flexible NLO Monte Carlo tools for accurate LHC analyses of W γ γ and related processes, with direct implications for SM background estimates and constraints on gauge couplings.

Abstract

The computation of the NLO-QCD corrections to the cross sections for W γγproduction in hadronic collisions is presented. We consider the case of real photons in the final state, but include full leptonic decays of the W. Numerical results for the LHC and the Tevatron are obtained through a parton level Monte Carlo based on the structure of the VBFNLO program, allowing an easy implementation of general cuts and distributions. We show the dependence on scale variations of the integrated cross sections and provide evidence of the fact that NLO QCD corrections strongly modify the LO predictions for observables at the LHC both in magnitude and in shape.

Figures (13)

• Figure 1: Examples of the three topologies of Feynman diagrams contributing to the process $pp\to$$W^\pm\gamma\gamma$ + X at tree-level.
• Figure 2: Left:Scale dependence of the total LHC cross section for $p p \to W^-\gamma\gamma +X \to \ell^- \gamma \gamma +=\hbox{$p$}p \hbox{/} _T+X$ at LO and NLO within the cuts of Eqs. (\ref{['eq:cuts']}, \ref{['eq:isol']}). The factorization and renormalization scales are together or independently varied in the range from $0.1 \cdot \mu_0$ to $10 \cdot \mu_0$.Right:Same as in the left panel but for the different NLO contributions at $\mu_F=\mu_R=\xi\mu_0$.
• Figure 3: Same as Fig. \ref{['fig:2']}, but for $p p \to W^+\gamma\gamma +X \to \ell^+ \gamma \gamma +=\hbox{$p$}p \hbox{/} _T+X$ at the LHC.
• Figure 4: Left:Invariant mass distribution of the photon pair for $p p \to W^+ \gamma\gamma +X \to \ell^+ \gamma \gamma +=\hbox{$p$}p \hbox{/} _T+X$ production at the LHC. LO and NLO results are shown for $\mu_F=\mu_R=\mu_0$ and the cuts of Eqs. (\ref{['eq:cuts']}, \ref{['eq:isol']}).Right:K-factor as defined in Eq. (\ref{['eq:kfactor']}).
• Figure 5: Left:Transverse-momentum distribution of the hardest photon in $p p \to W^+\gamma\gamma +X \to \ell^+ \gamma \gamma +=\hbox{$p$}p \hbox{/} _T+X$ production at the LHC. LO and NLO results are shown for $\mu_F=\mu_R=\mu_0$ and the cuts of Eqs. (\ref{['eq:cuts']}, \ref{['eq:isol']}).Right:K-factor as defined in Eq. (\ref{['eq:kfactor']}).