  We investigate experimentally the number statistics of a mesoscopic ensemble
of cold atoms in a microscopic dipole trap loaded from a magneto-optical trap,
and find that the atom number fluctuations are reduced with respect to a
Poisson distribution due to light-assisted two-body collisions. For numbers of
atoms N>2, we measure a reduction factor (Fano factor) of 0.72+/-0.07, which
differs from 1 by more than 4 standard deviations. We analyze this fact by a
general stochastic model describing the competition between the loading of the
trap from a reservoir of cold atoms and multi-atom losses, which leads to a
master equation. Applied to our experimental regime, this model indicates an
asymptotic value of 3/4 for the Fano factor at large N and in steady state. We
thus show that we have reached the ultimate level of reduction in number
fluctuations in our system.
