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\begin{equation} 
\begin{split}
 |T|^2= frac{e^{4}}{s^{2}}\bar{u_{s1}}\gamma_{\nu} v_{s2}\bar{v_{s2\shortmid}}\gamma^{\nu}u_{s1}\bar{u_{s1\shortmid}} \gamma^{\mu}v_{s2\shortmid}\bar{v_{s2}}\gamma_{\mu}u_{s1}\\
 &= frac{e^{4}{s^{2}} Tr[u_{s1}\bar{u_{s1}}\gamma_{nu} v_{s2}\bar{v_{s2}}\gamma_{mu}] Tr[u_{s1\shortmid}\bar{u_{s1\shortmid}}\gamma^{mu} v_{s2\shortmid}\bar{v_{s2\shortmid}}\gamma^{nu}]
\end{split} 
\end{equation}

\documentclass{article}
\usepackage{mathtools}
\usepackage{MnSymbol}
\begin{document}

\begin{equation}
\begin{split}
 |T|^2&= \frac{e^{4}}{s^{2}}\bar{u_{s1}}
 \gamma_{\nu} v_{s2}\bar{v_{s2\shortmid}}
 \gamma^{\nu}u_{s1}\bar{u_{s1\shortmid}} 
 \gamma^{\mu}v_{s2\shortmid}\bar{v_{s2}}
 \gamma_{\mu}u_{s1}\\
 %
 &= \frac{e^{4}}{s^{2}} Tr[u_{s1}\bar{u_{s1}}
	 \gamma_{nu} v_{s2}\bar{v_{s2}}
 \gamma_{mu}] Tr[u_{s1\shortmid}\bar{u_{s1\shortmid}}
	 \gamma^{mu} v_{s2\shortmid}\bar{v_{s2\shortmid}}
 \gamma^{nu}]
\end{split}
\end{equation}
\end{document}