\documentclass{ppex}
\nonstopmode
\AtEndDocument {\end {fmffile}} \AtBeginDocument {\begin {fmffile}{ftmp}}
\usepackage {feynmp}
\pagestyle{empty}

\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {feynmp}
\begin{fmfgraph*}(100,60)
 \fmfleftn{i}{2} \fmfrightn{o}{4}
 \fmflabel{$e_-$}{i1}\fmflabel{$e_+$}{i2}
 \fmflabel{$\mu_+$}{o1}
 \fmflabel{$\nu_{\mu}$}{o2}
 \fmflabel{$s$}{o3}
 \fmflabel{$\bar c$}{o4}
 \fmf{fermion}{i1,v1,i2}
 \fmf{boson,label=$\gamma,,Z$}{v1,v2}
 \fmf{boson}{v3,v2,v4}
 \fmf{fermion}{o1,v3,o2}
 \fmf{fermion}{o4,v4,o3}
 \fmfdot{v1,v3,v4}\fmfblob{.12w}{v2}
\end{fmfgraph*}
\end{document}