Hamiltonian stationary Lagrangian surfaces of constant Gaussian curvature in complex space forms

Let $M$ be a connected Hamiltonian stationary Lagrangian surface of constant Gaussian curvature $K$ in a two-dimensional complex space form $\Mtilde^2(4ε)$ of constant holomorphic sectional curvature $4ε$, and let $H$ denote its mean curvature vector field. We prove that either $K=ε$ or $K=0\neε$ an