
\documentclass[border=5pt,multi=true]{standalone}
\usepackage{standalone}
\usepackage{ifthen}
\usepackage{microtype}
\usepackage{lineno}
\usepackage{xspace}
\usepackage{caption}
\usepackage{graphicx}
\usepackage{color}
\usepackage{colortbl}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{upgreek}
\usepackage{hyperxmp}
\usepackage{hyperref}
\usepackage{todonotes}
\usepackage{footmisc}
\usepackage{hypcap}
\usepackage{xspace}
\usepackage{upgreek}
\usepackage{cite}
\usepackage{mciteplus}
\usepackage{comment}
\usepackage{enumitem}
\usepackage{cleveref}
\usepackage{multirow}
\usepackage{placeins}
\usepackage{tikz}
\usepackage{longtable}
\usepackage{appendix}


\usetikzlibrary{trees,arrows,automata,shapes}
\tikzset
{
   vector/.style = {decorate, decoration={snake,amplitude=2pt, segment length=5pt}},
   fermion/.style = {postaction={decorate}, decoration={markings,mark=at position .55 with {\arrow{>}}}},
   fermionbar/.style = {postaction={decorate}, decoration={markings,mark=at position .55 with {\arrow{<}}}},
   gluon/.style = {decorate, decoration={coil,amplitude=3pt, segment length=5pt}},
   scalar/.style = {dashed, postaction={decorate}, decoration={markings,mark=at position .55 with {\arrow{>}}}},
   scalarbar/.style = {dashed, postaction={decorate}, decoration={markings,mark=at position .55 with {\arrow{<}}}}
}


\graphicspath{{./figs/}}

\begin{document}
\DeclareGraphicsExtensions{.pdf}
\begin{center}
\begin{tikzpicture}[scale=0.65]
    \draw [fermion, line width = 0.7pt] (0.,0) node[above]{$b$} -- (3.5,0);
    \draw [fermion, line width = 0.7pt] (3.5,0) -- (7,0) node[above]{$s$};
    \draw [vector, line width = 0.7pt] (3.0,0) -- (4.0,-2.5) node[midway,left]{$Z'~$};
    \draw [fermion,    line width = 0.7pt] (4.0,-2.5) -- (6.6,-3) node[right]{$\ell^-$};
    \draw [fermionbar, line width = 0.7pt] (4.0,-2.5) -- (6.6,-2) node[right]{$\ell^+$};
    \draw [fermion, line width = 0.7pt] (10.,0) node[above]{$b$} -- (13.5,0);
    \draw [fermion, line width = 0.7pt] (13.5,0) -- (17,0) node[above]{$\ell^-$};
    \draw [very thick,double, line width = 0.7pt] (13.0,0) -- (14.0,-2.5) node[midway,left]{$LQ~$};
    \draw [fermion,    line width = 0.7pt] (14.0,-2.5) -- (16.6,-3) node[right]{$s$};
    \draw [fermionbar, line width = 0.7pt] (14.0,-2.5) -- (16.6,-2) node[right]{$\ell^+$};
\end{tikzpicture}
\end{center}
\end{document}
