  We study theoretically, numerically, and experimentally the relaxation of a
collisionless gas in a quadrupole trap after a momentum kick. The
non-separability of the potential enables a quasi thermalization of the single
particle distribution function even in the absence of interactions.
Suprinsingly, the dynamics features an effective decoupling between the strong
trapping axis and the weak trapping plane. The energy delivered during the kick
is redistributed according to the symmetries of the system and satisfies the
Virial theorem, allowing for the prediction of the final temperatures. We show
that this behaviour is formally equivalent to the relaxation of massless
relativistic Weyl fermions after a sudden displacement from the center of a
harmonic trap.
