  A heuristic approach for collisionless perpendicular diffusion of energetic
particles is presented. Analytic forms for the corresponding diffusion
coefficient are derived. The heuristic approach presented here explains the
parameter $a^2$ used in previous theories in order to achieve agreement with
simulations and its relation to collisionless Rechester & Rosenbluth diffusion.
The obtained results are highly relevant for applications because previously
used formulas are altered significantly in certain situations.
