  We present a new technique for a numerical analysis of the phase structure of
the 2D Hubbard model as a function of the hole chemical potential. The grand
canonical partition function for the model is obtained via Monte Carlo
simulations. The dependence of the hole occupation number on the chemical
potential and the temperature is evaluated. These calculations, together with a
study of the Yang-Lee zeros of the grand canonical partition function, show
evidence of a phase transition at zero temperature and particle density below
half-filling. The binding energy of a pair of holes is calculated in the low
temperature regime and the possibility for pairing is explored.
