Azimuthal angle dependence of pion femtoscopy in &[root]s_NN = 200 GeV Cu+Au collisions at STAR

HBT measurements provide opportunity to investigate the source shape at freeze-out and have access to its spatial and temporal development in relativistic heavy ion collisions. Especially, azimuthal dependence of HBT radii with respect to the n^th-order event plane reveals the property of the expanding medium and the difference between initial and final source eccentricities.
 In Cu+Au collisions, there is an initial asymmetric density gradient due to the asymmetry in number of participants. It generates a difference of source expansion in forward and backward directions. Comparing the HBT radii by such an initial shape will help in further understanding of the expansion dynamics.
 In this talk, we will present the results of azimuthal dependence of HBT radii in Cu+Au collisions as well as two-particle average momentum and centrality dependences. The results will be compared to those obtained for Au+Au collisions.