% !TEX program = pdflatexmk
% !TEX parameter = -shell-escape
% Author: Izaak Neutelings (December 24)
% Instructions: To compile via command line, run the following twice
%   pdflatex -shell-escape extract/singletop$TAG.tex
\documentclass[11pt,border=4pt]{standalone}
\usepackage{feynmp-auto}
\begin{document}
\begin{fmffile}{feyngraph}
  \fmfframe(-10,10)(2,9){ % padding (L,T)(R,B)
  \begin{fmfgraph*}(110,70) % dimensions (WH)
    % line style
    \fmfset{wiggly_len}{12} % boson wavelength
    \fmfset{wiggly_slope}{65} % boson slope of waves
    % external vertices
    \fmfleft{i2,i1}
    \fmfright{o2,z,o1}
    \fmfshift{4 left}{z}
    % skeleton
    \fmf{fermion}{i1,v1,o1}
    \fmf{fermion}{i2,v2,o2} % top quark
    \fmf{phantom,t=0.25}{v1,v2} % pull Vqq vertices together
    \fmf{phantom,t=0.60}{v1,i1,i2,v2} % pull Vqq vertices to left
    \fmffreeze
    % VV -> Z
    \fmf{boson,t=1.3,l.s=right,l.d=-3,label=W$^+$\hspace{6pt}}{v1,v}
    \fmf{boson,t=1.3,l.s=left,l.d=-4,label=W$^-$\hspace{6pt}}{v2,v}
    \fmf{boson,t=1.7}{v,z} % Z boson
    %%%% coupling
    %%%\fmfv{d.sh=circle,d.f=full,d.si=4,f=(1,,0,,0)}{v2}
    % labels
    \fmfv{l.a=158,l.d=5,l=$q$}{i1}
    \fmfv{l.a=-158,l.d=5,l=b}{i2}
    \fmfv{l.a=22,l.d=5,l=$q'$}{o1}
    \fmfv{l.a=0,l.d=4,l=Z}{z}
    \fmfv{l.a=-22,l.d=5,l=t}{o2}
  \end{fmfgraph*}
  } % close \fmfframe
\end{fmffile}
\end{document}