\documentclass{article}
\usepackage[paperheight=60mm,paperwidth=95mm, margin=5mm]{geometry}
\usepackage{feynmp-auto}
\addtolength{\oddsidemargin}{-10mm}
\addtolength{\evensidemargin}{-10mm}
% commas in feynmp sometimes lead to strange errors, use \comma instead
\DeclareMathSymbol{\comma}{\mathpunct}{letters}{"3B}

\begin{document}\LARGE
    \centering
    \begin{fmffile}{O3_6_diagram} \centering 
       \begin{fmfgraph*}(300,130)
           \fmfstraight   
           \fmfleft{l0,l1,l2,l3,l4}
           \fmfright{r0,r1,r2,r3,r4}           
           
           \fmf{phantom}{l4,a1,a2,r4}  
           \fmf{phantom}{l3,b1,r3}  
           \fmf{phantom}{l2,c1,r2}            
           \fmf{phantom}{l1,d1,r1}
           \fmf{phantom}{l0,e1,e2,r0}
           
           \fmffreeze
                      
           \fmf{fermion,label=$b$,tension=1,label.side=right}{l4,a1}
           \fmf{photon,label=$W^-$,tension=1,label.side=right}{a1,a2}               
           \fmf{fermion,label=$s$, tension=1}{a2,r4}            
                      
           \fmf{fermion,right=0.5,tension=0.5}{a1,c1,a2}
           \fmfv{label=$\bar{u}\comma \bar{c} \comma \bar{t}$,label.angle=80}{c1}
                      
           \fmf{gluon,label=$g$,tension=0.7,label.side=left}{d1,c1}  
           
           \fmf{fermion,label=$l^-$,tension=-0.475,label.side=left}{d1,r2}
           \fmf{fermion,label=$l^+$,tension=0.6}{r0,d1}                   
           
           %  \fmf{phantom, tension = 1.5}{l2,l1}
       \end{fmfgraph*}
   \end{fmffile}
    \pagestyle{empty}
\end{document}