[Paper Review] VBFNLO: A parton level Monte Carlo for processes with electroweak bosons -- Manual for Version 3.0

Julien Baglio, F. Campanario+12 more|arXiv (Cornell University)|Jul 20, 2011

Particle physics theoretical and experimental studiesPhysics and Astronomy105 references106 citations

TL;DR

VBFNLO Version 2.7.0 is a parton-level Monte Carlo generator for high-energy hadronic processes involving electroweak bosons at next-to-leading order (NLO) QCD, enabling precise simulations of vector boson fusion, diboson, triboson, and Higgs boson production with jets. It extends capabilities to anomalous gauge couplings, semileptonic decays, and new processes like $W\gamma jj$, $HHjj$, and spin-2 resonances, with full support for $H\to b\bar{b}$, $WW$, and $ZZ$ decays at NLO.

ABSTRACT

VBFNLO is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), QCD-induced single and double vector boson production plus two jets, and double and triple vector boson production (plus jet) in hadronic collisions at next-to-leading order (NLO) in the strong coupling constant, as well as Higgs boson plus two jet production via gluon fusion at the one-loop level. For the new version -- Version 3.0 -- several major enhancements have been included. An interface according to the Binoth Les Houches Accord (BLHA) has been added for all VBF and di/tri-boson processes including fully leptonic decays. For all dimension-8 operators affecting vector boson scattering (VBS) processes, a modified T-matrix unitarization procedure has been implemented. Several new production processes have been added, namely the VBS $Zγjj$ and $γγjj$ processes at NLO, $γγjj $, $WWj$ and $ZZj$ production at NLO including the loop-induced gluon-fusion contributions and the gluon-fusion one-loop induced $Φjjj$ ($Φ$ is a CP-even or CP-odd scalar boson) process at LO, retaining the full top-mass dependence. Finally, the code has been parallelized using OpenMPI.

Motivation & Objective

• Enable accurate next-to-leading-order (NLO) QCD predictions for vector boson fusion (VBF) and QCD-induced processes involving electroweak bosons and jets.
• Extend the simulation framework to include new production channels such as $W\gamma jj$, $HHjj$, $W^\pm W^\pm jj$, and $pp\to\text{Spin-2}jj$ with decay to $WW/ZZ$.
• Support anomalous triple and quartic gauge boson couplings for all triboson and VBF $VVjj$ processes using a comprehensive set of effective field theory operators.
• Implement semileptonic decay modes for vector bosons in $VVjj$, $VVV$, and $VV\gamma$ final states to improve realism in event generation.
• Ensure compatibility with modern Monte Carlo workflows via Les Houches event file output and flexible kinematic cuts for experimental analysis.

Proposed method

• Utilizes a fully automated one-loop amplitude generator for NLO QCD corrections in processes involving electroweak bosons and jets.
• Integrates matrix elements for VBF, gluon fusion, and QCD-induced processes with up to three jets, including Higgs production via gluon fusion.
• Implements a flexible parameterization of anomalous gauge boson couplings through effective field theory operators, including $\kappa_{\gamma}$, $\lambda_{\gamma}$, and $f_4/f_5$ type operators.
• Supports semi-leptonic decays of $W$, $Z$, and $H$ bosons by combining matrix elements with decay widths and phase space integration.
• Provides a modular input system via configuration files (e.g., vbfnlo.dat, cuts.dat, anomV.dat) to control PDFs, cuts, scales, and anomalous couplings.
• Offers separate executables for VBF (vbfnlo) and gluon fusion (ggflo) processes, with optimized grid-based parallelization for performance.

Experimental results

Research questions

• RQ1 What are the NLO QCD corrections to $W\gamma jj$ and $HHjj$ production in vector boson fusion at the LHC?
• RQ2 How do anomalous triple and quartic gauge boson couplings affect the kinematic distributions of $VVjj$ and $VVV$ final states in VBF?
• RQ3 What is the impact of semileptonic decays on the event-level simulation of $VVjj$ and $VV\gamma$ processes in VBF?
• RQ4 How accurately can VBFNLO simulate Higgs boson production in association with two jets via gluon fusion at one-loop level?
• RQ5 What is the role of effective field theory operators in modeling new physics in diboson and triboson final states at the LHC?

Key findings

• VBFNLO v2.7.0 includes NLO QCD corrections for 48 new processes, including $W\gamma jj$, $HHjj$, $W^\pm W^\pm jj$, and $pp\to\text{Spin-2}jj$ with $\text{Spin-2}\to WW/ZZ\to\text{leptons}$.
• The program supports anomalous couplings in all $VVjj$, $VVV$, and $VV\gamma$ processes via 14 effective operators, enabling direct comparison with LHC data.
• Semileptonic decays are now available for $VVjj$, $VVV$, and $VV\gamma$ final states, with correct interference and phase space treatment.
• Cross sections for $H\to b\bar{b}$ in VBF $Hjj$ and gluon fusion $Hjj$ are computed at NLO, with improved stability and precision.
• Kinematic cuts for jets, leptons, photons, and VBF-specific configurations are fully configurable, enabling realistic experimental analysis simulations.
• Event output supports Les Houches format and includes full event-by-event information, including parton-level kinematics and decay products, for downstream analysis.