This is a copy of the diagram from Wikipedia. I produced this using codes developed by me as previously instructed here with other examples. — What to do when its 2 am around here, you are fresh but nowhere to go.

Here is the code:

% Feynman diagram

% Requires PGF >= 2.0

\documentclass{article}

\usepackage[latin1]{inputenc}

\usepackage{tikz}

\usetikzlibrary{trees}

\usetikzlibrary{decorations.pathmorphing}

\usetikzlibrary{decorations.markings}

\usepackage{verbatim}