Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2016 / S19 / 2 / a

At zero dispersion and $\alpha =0$, $\sigma =\sqrt{ϵ\beta }$ and ${\sigma }^{\prime }=\sqrt{ϵ/\beta }$. The results areThe repeated $D_x,D_y$ entries in the source are interpreted as intended vanishing dispersion and its slope. If dispersion slopes were not zero, energy spread would contribute to divergence and further data would be needed.