  Reproducing measurements of the scattering mean free paths for energetic
particles propagating through the solar system has been a major problem in
space physics. The pioneering work of Bieber et al. [Astrophys. J. 420, 294
(1994)] provided a theoretical explanation of such observations, which,
however, was based on assumptions such as the questionable hypothesis that
quasi-linear theory is correct for parallel diffusion. By employing a hybrid
plasma-wave/magnetostatic turbulence model, a test-particle code is used to
investigate the scattering of energetic particles. The results show excellent
agreement with solar wind observations.
