The Long Slow Death of the HBT Puzzle

At the onset of the RHIC era femtoscopic source sizes inferred from two-particle correlations at RHIC defied description with hydrodynamic models. This failure, which became known as the HBT puzzle, now appears to be solved. The source of the discrepancy appears to be a conspiracy of several factors, each of which contributed to making the evolution of RHIC collisions more explosive. These included pre-equilibrium flow, using a stiffer equation of state and adding viscosity.