  The diffusion properties of self-propelled particles which move at constant
speed and, in addition, reverse their direction of motion repeatedly are
investigated. The internal dynamics of particles triggering these reversal
processes is modeled by a stochastic clock. The velocity correlation function
as well as the mean squared displacement is investigated and, furthermore, a
general expression for the diffusion coefficient for self-propelled particles
with directional reversal is derived. Our analysis reveals the existence of an
optimal, finite rotational noise amplitude which maximizes the diffusion
coefficient. We comment on the relevance of these results with regard to
microbiological systems and suggest further experiments in this context.
