Femtoscopy in Relativistic Heavy-Ion Collisions as a probe of system collectivity

The collision of ultrarelativistic heavy-ions creates a system that rapidly evolves and emits a significant number of hadrons. The femtoscopy technique is able, through the analysis of two-particle correlations, to measure the space-time extent of the system at the point of this emission. I will show how these results can then be used to probe the dynamics of the system and, in particular, provide evidence that it behaves collectively, as a single piece of matter. This is especially interesting at the SPS and RHIC energies, where the system is predicted to go through a deconfined state and will continue to be relevant in PbPb collisions at the LHC. Hydrodynamic models aim to describe the behaviour of the system and provide predictions for both the system size and its dependence on the evolution dynamics. I present experimental femtoscopic results and confront them with hydrodynamic predictions and discuss their validity. I also show extrapolations to the LHC regime both for heavy-ion and proton-proton collisions. (author)