[Tex/LaTex] Feynman Diagram (with Tikz-Feynman) that involves a big blob

Question

I'm new to Latex and wanted to use a certain Feynman Diagram. My problem is, that I don't know, how to draw something like this with Tikz-Feynman:

It's supposed to be a 4-point vertex, where the interaction is represented by the oval blob and transmits momentum P. The arrows at the end of the legs represent the spin.
It would be nice, if someone had a suggestion for making such a thing, with a special label for the text (where I could fill in the momenta/ spin)

Thanks in advance!

Answer 1

You have to position the vertices manually.

\documentclass{article}
\usepackage{tikz-feynman,contour}
\begin{document}
\begin{figure}
  \centering
  \begin{tikzpicture}
    \begin{feynman}
      \vertex[blob,label={right:$p$}] (m) at ( 0, 0) {\contour{white}{$\uparrow$}};
      \vertex (a) at (-1,-2) {$\uparrow$};
      \vertex (b) at ( 1,-2) {$\downarrow$};
      \vertex (c) at (-1, 2) {$\uparrow$};
      \vertex (d) at ( 1, 2) {$\downarrow$};
      \diagram* {
        (a) -- [fermion,edge label=$-k$] (m) -- [fermion,edge label=$-k'$] (c),
        (b) -- [fermion,edge label'=$k+p$] (m) -- [fermion,edge label'=$k'+p$] (d),
      };
    \end{feynman}
  \end{tikzpicture}
  \caption{Scattering at a 4-vertex.}
\end{figure}
\end{document}