Transverse momentum dependence of HBT radii from an opaque source with hydrodynamic flow

The RHIC HBT puzzle is one of most interesting results from recent RHIC experiment. Based on a hydrodynamical model, we investigatethe HBT radii at 200A GeV Au+Au collisions. We focus on the effect of opaqueness of the source caused by restricted emission angle for pionsas well as the one caused by strong transverse expansion. It is shown thattransverse expansion dominates the HBT radii at higher pair transverse momenta than a few hundred MeV. As a result, the naive opaque source model fails to resolve the HBT puzzle.