Femtoscopy in hadron and lepton collisions: RHIC results and world systematics

Femtoscopic measurements at a variety of facilities have established a clear dependence of spatial scales with event multiplicity and particle transverse mass ($m_T$) in heavy ion collisions from $\sqrt(s_{NN}) \sim 2-200 GeV$. The $m_T$-dependence is thought to arise from collective, explosive flow of the system, as probed by independent measurements, while the multiplicity dependence reflects the increased spatial extent of the final state with decreasing impact parameter. Qualitatively similar dependences have been reported from high energy hadron and lepton collisions, where the conceptual validity of an impact parameter or collective flow are less clear. We focus on results from elementary particle collisions, identify trends seen in the experimental data and compare them to those from heavy ion collisions.