  When a dense granular jet hits a target, it forms a large dead zone and
ejects a highly collimated conical sheet with a well-defined opening angle.
Using experiments, simulations, and continuum modeling, we find that this
opening angle is insensitive to the precise target shape and the dissipation
mechanisms in the flow. We show that this surprising insensitivity arises
because dense granular jet impact, though highly dissipative, is nonetheless
controlled by the limit of perfect fluid flow.
