  Parity-odd domains, corresponding to non-trivial topological solutions of the
QCD vacuum, might be created during relativistic heavy ion collisions. These
domains are predicted to lead to charge separation of quarks along the system's
orbital momentum axis. We investigate a three particle azimuthal correlator
which is a \P even observable, but directly sensitive to the charge separation
effect. We report measurements of charged hadrons near center-of-mass rapidity
with this observable in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$=200 GeV
using the STAR detector. A signal consistent with several expectations from the
theory is detected. We discuss possible contributions from other effects that
are not related to parity violation.
