  We study the number statistics of ultracold bosons in optical Lattice using
the slave particle technique and quantum Monte Carlo simulations. For
homogeneous Bose-Hubbard model, we use the slave particle technique to obtain
the number statistics near the superfluid to normal-liquid phase transition.
The qualitatively behavior agree with the recent experiment probing number
fluctuation [Phys. Rev. Lett. \textbf{96}, 090401 (2006)]. We also perform
quantum Monte Carlo simulations to 1D system with external harmonic trap. The
results qualitatively agree with the experiments.
