Full counting statistics of a charge shuttle

We study the charge transfer in a small grain oscillating between two leads. Coulomb blockade restricts the charge fluctuations in such a way that only zero or one additional electrons can sit on the grain. The system thus acts as a charge shuttle. We obtain the full counting statistics of charge transfer and discuss its behavior. For large oscillation amplitude the probability of transferring n electrons per cycle is strongly peaked around one. The peak is asymmetric since its form is controlled by different parameters for n>1 and n<1. Under certain conditions the systems behaves as if the effective charge is 1/2 of the elementary one. Knowledge of the counting statistics gives a new insight on the mechanism of charge transfer.