Full code to produce a multipage PDF with the standalone diagrams depicting ttbar production and decay:

ttbar.tex

% !TEX program = pdflatexmk
% !TEX parameter = -shell-escape
% Author: Izaak Neutelings (February 2023)
\documentclass[10pt,border=2pt,multi=page,crop]{standalone}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{feynmp-auto}
 
\newcommand{\Pom}{\rm I\!P} % Pomeron
 
\begin{document}
\large
 
% TTBAR PRODUCTION - Quark-antiquark annihilation
\begin{page}
\fmfframe(-6,15)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-qq}
  \begin{fmfgraph*}(110,60)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    % main
    \fmf{fermion}{i1,v1,i2}
    \fmf{fermion}{o2,v2,o1}
    \fmf{gluon,label=$g$,label.side=right,label.dist=10}{v2,v1}
    % labels
    \fmflabel{$q$}{i1}
    \fmflabel{$\overline{q}$}{i2}
    \fmflabel{$\overline{\text{t}}$}{o2}
    \fmflabel{t}{o1}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION - Gluon-gluon fusion (s-channel)
\begin{page}
\fmfframe(-6,15)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-gg-t}
  \begin{fmfgraph*}(110,60)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    \fmfshift{2 left}{i1}
    % main
    \fmf{fermion}{o2,v2,o1}
    \fmf{gluon}{v1,i1}
    \fmf{gluon}{v1,i2}
    \fmf{gluon,label=$g$}{v1,v2}
    % labels
    %\fmflabel{$g$}{i1}
    %\fmflabel{$g$}{i2}
    \fmfv{l.d=4,l=$g$}{i1}
    \fmfv{l.d=6,l=$g$}{i2}
    \fmflabel{$\overline{\text{t}}$}{o2}
    \fmflabel{t}{o1}
    %\fmflabel{$i\sqrt{\alpha}$}{v1}
    %\fmflabel{$i\sqrt{\alpha}$}{v2}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION - Gluon-gluon fusion (s-channel) 2
\begin{page}
\fmfframe(-6,15)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-gg-t}
  \begin{fmfgraph*}(110,60)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    % main
    \fmf{fermion}{o2,v2,o1}
    \fmf{gluon}{v1,i1}
    \fmf{gluon}{i2,v1}
    \fmf{gluon,label=$g$}{v1,v2}
    % labels
    \fmflabel{$g$}{i1}
    \fmflabel{$g$}{i2}
    \fmflabel{$\overline{\text{t}}$}{o2}
    \fmflabel{t}{o1}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION - Gluon-gluon fusion (t-channel)
\begin{page}
\fmfframe(-6,15)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-gg-s}
  \begin{fmfgraph*}(110,60)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    % main
    \fmf{gluon}{v1,i1}
    \fmf{fermion}{v1,o1}
    \fmf{gluon}{i2,v2}
    \fmf{fermion}{o2,v2}
    \fmf{fermion,label=t}{v2,v1}
    % labels
    \fmflabel{$g$}{i2}
    \fmflabel{$g$}{i1}
    \fmfv{l.d=7,l.a=22,l=t}{o1}
    \fmfv{l.d=7,l.a=-20,l=$\overline{\text{t}}$}{o2}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION - Quark-antiquark annihilation + radiation
\begin{page}
\fmfframe(-6,18)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-qq-q}
  \begin{fmfgraph*}(120,70)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    \fmftop{t}
    \fmfshift{5 up}{t}
    % skeleton
    \fmf{phantom}{i1,v1,i2}
    \fmf{phantom}{o1,v2,o2}
    \fmf{phantom}{v1,v2}
    \fmffreeze
    % main
    \fmf{fermion}{i1,g}
    \fmf{plain,tension=2.8}{g,v1}
    \fmf{fermion}{v1,i2}
    \fmf{gluon,tension=0}{t,g}
    \fmf{gluon}{v1,v2}
    \fmf{fermion}{o2,v2,o1}
    % labels
    \fmflabel{$q$}{i1}
    \fmflabel{$\overline{q}$}{i2}
    \fmfv{l.d=5,l.a=25,l=$g$}{t}
    \fmflabel{$\bar{\text{t}}$}{o2}
    \fmflabel{$\text{t}$}{o1}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION - Gluon-gluon fusion + radiation
\begin{page}
\fmfframe(-6,18)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-gg-q}
  \begin{fmfgraph*}(120,75)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    \fmftop{t}
    \fmfshift{4 left}{i1}
    \fmfshift{2 left}{i2}
    \fmfshift{5 up}{t}
    % skeleton
    \fmf{phantom}{i1,v1,i2}
    \fmf{phantom}{o1,v2,o2}
    \fmf{phantom,tension=1.2}{v1,v2}
    \fmffreeze
    % main
    \fmf{gluon,tension=0.8}{g,i1}
    \fmf{fermion}{v1,g}
    \fmf{gluon}{v1,i2}
    \fmf{fermion,tension=0}{g,t}
    \fmf{gluon}{v1,v2}
    \fmf{fermion}{o2,v2,o1}
    % labels
    %\fmflabel{$g$}{i1}
    %\fmflabel{$g$}{i2}
    \fmfv{l.d=4,l=$g$}{i1}
    \fmfv{l.d=6,l=$g$}{i2}
    \fmfv{l.d=5,l.a=25,l=$q$}{t}
    \fmflabel{$\bar{\text{t}}$}{o2}
    \fmflabel{$\text{t}$}{o1}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION - Quark-gluon fusion + radiation
\begin{page}
\fmfframe(-6,18)(-6,15){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-gq-q}
  \begin{fmfgraph*}(120,75)
    \fmfleft{i2,i1}
    \fmfright{o2,o1}
    \fmftop{t}
    \fmfshift{4 left}{i1}
    \fmfshift{2 left}{i2}
    \fmfshift{5 up}{t}
    % skeleton
    \fmf{phantom}{i1,v1,i2}
    \fmf{phantom}{o1,v2,o2}
    \fmf{phantom,tension=1.2}{v1,v2}
    \fmffreeze
    % main
    \fmf{gluon,tension=0.8}{g,i1}
    \fmf{fermion}{v1,g}
    \fmf{fermion}{i2,v1}
    \fmf{fermion,tension=0}{g,t}
    \fmf{gluon}{v1,v2}
    \fmf{fermion}{o2,v2,o1}
    % labels
    %\fmflabel{$g$}{i1}
    %\fmflabel{$g$}{i2}
    \fmfv{l.d=4,l=$g$}{i1}
    \fmfv{l.d=6,l=$q$}{i2}
    \fmfv{l.d=5,l.a=25,l=$q$}{t}
    \fmflabel{$\bar{\text{t}}$}{o2}
    \fmflabel{$\text{t}$}{o1}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION + DECAY
\begin{page}
\fmfframe(-1,15)(30,16){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-qq-decay}
  \begin{fmfgraph*}(160,140)
    \fmfset{arrow_len}{3.5mm}
    \fmfstraight
    \fmfleft{i1,i2,i3,i4,i5}
    \fmfright{o1,o2,o3,o4,o5,o6}
    % qq -> g
    \fmfshift{5 down}{i4}
    \fmfshift{5 up}{i2}
    \fmf{fermion,t=1.5}{i4,vg,i2}
    \fmf{gluon,t=1.5}{vtt,vg}
    \fmf{phantom,t=1.2}{v1,vtt,v2} % balance
    \fmf{phantom,t=0.7}{v1,o1} % balance
    \fmf{phantom,t=0.7}{v2,o6} % balance
    %\fmf{phantom,t=0.2}{v1,i2}
    %\fmf{phantom,t=0.2}{v2,i4}
    \fmflabel{$\overline{q}$}{i2}
    \fmflabel{$q$}{i4}
    \fmffreeze
    % tt
    \fmf{fermion,t=1.4}{v1,vtt,v2}  % top quark pair
    \fmf{phantom,label={$\overline{\text{t}}$},t=0,l.s=right}{vtt,v1} % top label
    \fmf{phantom,label={$\text{t}$},t=0,l.s=left}{vtt,v2} % top label
    \fmf{phantom,t=1}{o1,v1,o2} % balance
    \fmf{phantom,t=1}{o5,v2,o6} % balance
    \fmf{phantom,t=0.5}{i1,v1,v2,i5} % balance
    \fmffreeze
    % bW -> bqq
    \fmf{boson,t=1.2,label={$\text{W}^+$},l.d=5,l.s=right}{v2,w2}  % W boson
    \fmf{fermion}{v2,o6} % b quark
    \fmf{fermion}{o5,w2,o4}
    % bW -> blnu
    \fmf{boson,t=1.2,label={$\text{W}^-$},l.d=5,l.s=left}{v1,w1}  % W boson
    \fmf{fermion}{v1,o1} % b quark
    \fmf{fermion}{o2,w1,o3}
    % labels
    \fmflabel{\makebox[3.2mm][l]{$\overline{\nu}_\ell$} /\, q}{o2}
    \fmflabel{\makebox[3.2mm][l]{$\ell^-$} /\, $\overline{\text{q}}'$}{o3}
    \fmflabel{$\overline{\text{b}}$}{o1}
    \fmflabel{\makebox[3.2mm][l]{$\overline{\text{q}}'$} /\, $\nu_\ell$}{o4}
    \fmflabel{\makebox[3.2mm][l]{q} /\, $\ell^+$}{o5}
    \fmflabel{$\text{b}$}{o6}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
% TTBAR PRODUCTION + DECAY (round)
\begin{page}
\fmfframe(-1,15)(30,16){ % padding (LTRB)
\begin{fmffile}{feynmp-ttbar-qq-decay-round}
  \begin{fmfgraph*}(160,140)
    \fmfset{arrow_len}{3.5mm}
    %\fmfset{wiggly_len}{4mm}
    %\fmfstraight
    \fmfleft{i1,i2,i3,i4,i5}
    \fmfright{o1,o2,o3,o4,o5,o6}
    % qq -> g
    \fmfshift{5 down}{i4}
    \fmfshift{5 up}{i2}
    \fmf{fermion,t=1.5}{i4,vg,i2}
    \fmf{gluon,t=1.5}{vtt,vg}
    \fmf{phantom,t=1.4}{v1,vtt,v2} % balance
    \fmf{phantom,t=0.8}{v1,o1} % balance
    \fmf{phantom,t=0.8}{v2,o6} % balance
    %\fmf{phantom,t=0.2}{v1,i2}
    %\fmf{phantom,t=0.2}{v2,i4}
    \fmflabel{$\overline{q}$}{i2}
    \fmflabel{$q$}{i4}
    \fmffreeze
    % tt
    \fmf{fermion,t=1.4}{v1,vtt,v2}  % top quark pair
    \fmf{phantom,label={$\overline{\text{t}}$},t=0,l.s=right}{vtt,v1} % top label
    \fmf{phantom,label={$\text{t}$},t=0,l.s=left}{vtt,v2} % top label
    \fmf{phantom,t=1}{o1,v1,o2} % balance
    \fmf{phantom,t=1}{o5,v2,o6} % balance
    \fmf{phantom,t=0.5}{i1,v1,v2,i5} % balance
    \fmffreeze
    % bW -> bqq
    \fmf{boson,t=1.6,label={$\text{W}^+$},l.d=5,l.s=right}{v2,w2}  % W boson
    \fmf{fermion}{v2,o6} % b quark
    \fmf{fermion}{o5,w2,o4}
    % bW -> blnu
    \fmf{boson,t=1.6,label={$\text{W}^-$},l.d=5,l.s=left}{v1,w1}  % W boson
    \fmf{fermion}{v1,o1} % b quark
    \fmf{fermion}{o2,w1,o3}
    \fmf{phantom,t=1}{w1,o3}
    \fmf{phantom,t=1}{w2,o4}
    % labels
    \fmflabel{$\overline{\nu}_\ell$ / q}{o2}
    \fmflabel{$\ell^-$ / $\overline{\text{q}}'$}{o3}
    \fmflabel{$\overline{\text{b}}$}{o1}
    \fmflabel{$\overline{\text{q}}'$ / $\nu_\ell$}{o4}
    \fmflabel{q / $\ell^+$}{o5}
    \fmflabel{$\text{b}$}{o6}
  \end{fmfgraph*}
\end{fmffile}
}
\end{page}
 
\end{document}