  We have analyzed the statistical distribution of the fluorescence signal
levels in a magneto-optical trap containing a few atoms and observed that it
strongly depends on the relative size of the bin time with respect to the trap
decay time. We derived analytic expressions for the signal distributions in two
limiting cases, long and short bin time limits, and found good agreement with
numerical simulations performed regardless of the size of the bin time. We
found an optimal size of the bin time for minimizing the probability of
indeterminate atom numbers while providing accurate information on the
instantaneous number of atoms in the trap. These theoretical results are
compared with actual experimental data. We observed super-Poisson counting
statistics for the fluorescence from trapped atoms, which might be attributed
to uncorrelated motion of trapped atoms in the inhomogeneous magnetic field in
the trap.
