Two charges of $-4 \mu \mathrm{C}$ and $+4 \mu \mathrm{C}$ are placed at the points $\mathrm{A}(1,0,4) \mathrm{m}$ and $\mathrm{B}(2,-1,5) \mathrm{m}$ located in an electric field $\vec{E}=0.20 \mathrm{iV} / \mathrm{cm}$. The magnitude of the torque acting on the dipole is $8 \sqrt{\alpha} \times 10^{-5} \mathrm{Nm}$, Where $\alpha=$. $\_\_\_\_$