Correlations of particles produced in heavy ion collisions are sensitive to the space-time structure of the emitting system because of strong and Coulomb Final State Interactions. Moreover, non-identical particle correlations are a unique tool to probe the system collective expansion. The STAR experiment at RHIC allows to measure correlations of non-identical particles with close velocities. We have performed such an analysis from data obtained by the STAR detector for Au+Au collisions at 130 GeV and 200 GeV. The first results indicate that the average space-time emission points of pions, kaons and protons are different. The origin of such differences can be related to the time shift in the emission of different particle species or/and to the strong transverse radial flow. This result provides a new independent evidence that the system created at RHIC undergoes a strong collective transverse expansion.

PACS numbers: 25.75.--q, 25.75.Gz, 25.75.Ld, 25.75.Nq