Gluon-Induced Weak Boson Fusion

TL;DR

The paper quantifies gluon-induced NNLO color-exchange effects in Higgs production via weak boson fusion, focusing on diagrams with purely gluonic initial states. Using established one-loop techniques and Monte Carlo integration, it finds that these contributions are at the percent level under minimal cuts and are dramatically suppressed by typical WBF cuts (roughly a 30-fold reduction). The results indicate that the WBF signal remains robust against such color-exchange backgrounds and are consistent with interference studies with gluon fusion. Overall, the work supports the reliability of WBF as a Higgs discovery channel at the LHC and informs background considerations at NNLO accuracy.

Abstract

The gluon-gluon induced terms for Higgs production through weak boson fusion (WBF) are computed. Formally, these are of NNLO in the strong coupling constant. This is the lowest order at which non-zero color exchange occurs between the scattering quarks, leading to a color field and thus additional hadronic activity between the outgoing jets. Using a minimal set of cuts, the numerical impact of these terms is at the percent level with respect to the NLO rate for weak boson fusion. Applying the so-called WBF cuts leads to an even stronger suppression, so that we do not expect a significant deterioration of the WFB signal by these color exchange effects.

Figures (8)

• Figure 1: Leading order contributions to (a) weak boson fusion and (b) Higgs-Strahlung; (c) is the crossed .9 LO amplitude for .9 WBF. The straight solid lines denote quarks ($u,d,c,s,b$), the wiggle lines denote $W$ or $Z$ bosons, and the dashed line means a Higgs boson.
• Figure 2: .9 NLO contributions to .9 WBF: (a) .9 DIS-like and (b) color-exchange diagrams. Notation for the straight and wiggle lines is like in Fig. \ref{['fig::lo']}; spiral lines denote gluons.
• Figure 3: .9 NNLO .9 QCD contributions to .9 WBF: (a), (b) .9 DIS-like diagrams and (c), (d) color-exchange contributions. Notation is like in Fig. \ref{['fig::nlo']}.
• Figure 4: Diagrams at ${\cal O}(\alpha^3\alpha_s^2)$ which involve closed quark loops. The notation is as in Fig. \ref{['fig::nlo']}, except that the wiggle lines can only be $Z$ bosons here, and the particle in the loop can be a top quark.
• Figure 5: .9 NNLO contributions to .9 WBF that contain only a single quark line. Shown are only the diagrams with purely gluonic initial state. $qg$, $\bar{q}g$, and $q\bar{q}$ initial state contributions are obtained from them by crossing the external quark and gluon legs. Notation is like in Fig. \ref{['fig::nlo']}.