Monte Carlo tools for studies of non-standard electroweak gauge boson interactions in multi-boson processes: A Snowmass White Paper

TL;DR

This Snowmass White Paper analyzes how an effective field theory (EFT) framework with dimension-$6$ and dimension-$8$ operators can capture non-standard electroweak interactions in multi-boson processes and vector-boson scattering. It details the implementation of these operators in public Monte Carlo tools (MadGraph5, VBFNLO, WHIZARD), maps EFT coefficients to anomalous-coupling parametrizations, and discusses unitarity issues with form factors and unitarization schemes. The work presents tuned cross-checks among MG5, VBFNLO, and WHIZARD, assesses higher-order corrections (NLO QCD and electroweak effects), and provides practical conventions for using these tools in LHC EW studies. Overall, it offers a cohesive set of methods and benchmarks for studying non-standard EW physics with current MC programs while ensuring consistent comparisons across platforms.

Abstract

In this Snowmass 2013 white paper, we review the effective field theory approach for studies of non-standard electroweak interactions in electroweak vector boson pair and triple production and vector boson scattering. We present an overview of the implementation of dimension six and eight operators in MadGraph5, VBFNLO, and WHIZARD, and provide relations between the coefficients of these higher dimensions operators used in these programs and in the anomalous couplings approach. We perform a tuned comparison of predictions for multi-boson processes including non-standard electroweak interactions with MadGraph5, VBFNLO, and WHIZARD. We discuss the role of higher-order corrections in these predictions using VBFNLO and a POWHEG BOX implementation of higher-order QCD corrections to WWjj production. The purpose of this white paper is to collect useful tools for the study of non-standard EW physics at the LHC, compare them, and study the main physics issues in the relevant processes.

Figures (7)

• Figure 1: $m_{WW}$ distributions in $W$-pair production at the 14 TeV LHC are displayed on the l.h.s. for the SM (in blue) and for the SM plus the dimension six operator $\mathcal{O}_{WWW}$ with $c_{WWW}/\Lambda^2=6.25$ TeV (in red). Also shown is the unitarity bound Degrande:2012wf (in green). The figure on the r.h.s. shows the $m_{WW}$ distribution for the production of one longitudinally and one transversally polarized $W$ boson, when considering the SM (solid blue line), only the interference between the SM and the dimension-six operator (solid red line), the sum of the two (dashed red line), only the square of the new physics amplitude (solid green line), and finally the total contribution from the SM and the dimension-six operator (dashed green line).
• Figure 2: Invariant-mass distribution of the two lepton, two neutrino system. Left: Differential cross section for the SM and with anomalous coupling $T_1$ at LO and NLO. Right: Differential K-factors for the SM and with anomalous coupling as well as the cross-section ratio between anomalous coupling and SM for LO and NLO.
• Figure 3: Invariant mass distribution of the charged lepton pair (left) and rapidity distribution of the third jet (right) in VBF-induced $e^+\nu_e\mu^+\nu_\mu jj$ production at the LHC with $\sqrt{s}=7$ TeV and the selection cuts described in the text. The lower panels show the respective ratios of the POWHEG+PYTHIA and the NLO-QCD results. Horizontal bars indicate statistical errors in each case.
• Figure 4: Transverse-momentum distribution of the harder photon. Left: Differential cross section for the SM and with anomalous coupling $T_6$ at LO and NLO. Right: Differential K-factors for the SM and with anomalous coupling as well as the cross-section ratio between anomalous coupling and SM for LO and NLO.
• Figure 5: Rapidity difference of the diphoton system and the lepton-neutrino system for the SM and the anomalous coupling scenario. Left: LO distributions Right: NLO distributions