The time evolution of the pitch angle is shown in Fig. 1
for a sample of typical single-particle trajectories (without any
averaging process). It is indeed confirmed that particles with
μ ≈ {0, ±1} almost retain their original pitch angle. However,
scattering through 90◦ can occur, a fact that is not included
in QLT. An introduction to analytical transport theories can be
found, e.g., in Schlickeiser (2002) and Shalchi (2009).