Bose-Einstein Correlations in a Fluid Dynamical Scenario for Proton-Proton Scattering at 7 TeV

Using a fluid dynamical scenario for $pp$ scattering at 7 TeV, we compute correlation functions for $\pi^+\pi^+$ pairs. Femtoscopic radii are extracted based on three-dimensional parametrizations of the correlation functions. We study the radii as a function of the transverse momenta of the pairs, for different multiplicity classes, corresponding to recent experimental results from ALICE. We find the same decrease of the radii with $k_T$, more and more pronounced with increasing multiplicity, but absent for the lowest multiplicities. In the model we understand this as transition from string expansion (low multiplicity) towards a three-dimensional hydrodynamical expansion (high multiplicity).