  Preliminary results of identical-particle correlations probing the geometric
substructure of the particle-emitting source at RHIC are presented. An
$m_T$-independent scaling of pion HBT radii from large (central Au+Au) to small
(p+p) collision systems naively suggests comparable flow strength in all of
them. Multidimensional correlation functions are studied in detail using a
spherical decomposition method. In the light systems, the presence of
significant long-range non-femtoscopic correlations complicates the extraction
of HBT radii.
