\begin{displaymath}
\sigma = \frac{\pi}{k^2}\frac{\left(2 J+1\right)}{\left(2 s_a+1
\right)\left(2 s_b +1\right)} 
\frac{{\Gamma}_i {\Gamma}_{tot}} {\left( E-M\right)^2+ {
\Gamma}^2_{tot}/4}
\end{displaymath}
