University of Otago physicist Niels Kjærgaard and his team have used extremely precisely controlled laser beams to confine, accelerate and gently collide ultracold atomic clouds of fermionic potassium.
This allowed them to directly observe a key principle of quantum theory, the Pauli Exclusion Principle.
This principle predicts a forbidden zone along a meridian of the spherical halo of scattered particles, which the Otago experiments indeed unveiled.
The dark band in the graphic shows a rule derived from the principle in action. This rule is that indistinguishable fermions cannot scatter out at 90 degrees to the collision axis.