\begin{equation}
{\sigma}_{\gamma\gamma\rightarrow t\bar{t} \left(g\right) }
=\frac{12\pi{\alpha}^2 Q^4}
{s} \beta \left[1+\frac{{4 \alpha}_s}{3 \pi}\left\{\frac{{\pi}^2}{2 \beta}
-\left(5-\frac{{\pi}^2}{4}\right)+O({\beta}^1)\right\}\right]
\label{entw}
\end{equation}
