Feynman diagram labels not appearing in MikTeX with feynmf

[thoms2543]

I am trying to draw feynman diagram by using LaTeX code but the label in the code do not appear in the pdf(only the diagram appear). I am using the MikTeX 2.8 in windows XP and userpackage is feynmf. I have try several time and search through the web but I can't figure out any solution for this. Is anybody know how to solve this problem?e.g. this following is the code from some source

\documentclass{article}
\usepackage{feynmf}
\begin{document}
\setlength{\unitlength}{1mm}
An example of a Feynman graph drawn with Thorsten Ohl's \texttt{feynmf} package.
\begin{center}
\begin{fmffile}{feynexa}
\begin{fmfchar*}(40,25)
\fmfleft{em,ep}
\fmf{fermion}{em,Zee,ep}
\fmf{photon,label=$Z$}{Zee,Zff}
\fmf{fermion}{fb,Zff,f}
\fmfright{fb,f}
\fmfdot{Zee,Zff}
\end{fmfchar*}
\end{fmffile}
\end{center}
\end{document}

I only manage to get the diagram but the label Z does not appear.

 

[Wrichik Basu]

I ran your code in Overleaf and got the following:

Seems there is no error in the code. Your MikTex might be the source of trouble. A reinstall might help.