  In quantum mechanics, a particle is best described by the wave packet instead
of the plane wave. Here, we study the wave-packet scattering problem in Weyl
semimetals with the low-energy Weyl fermions of different chiralities. Our
results show that the wave packet acquires a chirality-protected shift in the
single impurity scattering process. More importantly, the chirality-protected
shift can lead to an anomalous scattering probability, thus, affects the
transport properties in Weyl semimetals. We find that the ratio between the
transport lifetime and the quantum lifetime increases sharply when the Fermi
energy approaches to the Weyl nodes, providing an explanation on the
experimentally observed the ultrahigh mobility in topological (Weyl or Dirac)
semimetals.
