  A qualitative calculation and discussion of two vortex states collisions are
given in the scalar $\phi ^4$ model. Three kinds of vortex states -- Bessel,
general monochromatic, and Laguerre-Gaussian vortex states -- are considered.
It is found that the total final momentum distribution in collision of physical
vortex states displays general topological structures, which depend on the
initial vortex states' topological charges, which are proportional to the
orbital angular momenta. This peculiar matching provides a novel observable,
the topological number of momentum distribution, and it may represent a new
fascinating research direction in particle physics. We also find that the
situation when the angular momenta of the two colliding Laguerre-Gaussian
states combine to zero can be recognized by the total final momentum
distribution close to the collision axis. Both features can be used to measure
the orbital angular momentum of vortex states.
