  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.

Nuclear Experiment;High Energy Physics - Phenomenology