Lower-bound estimate of the energy density times the formation time $\tau$ in pp, \pPb, and \PbPb\ collisions at $\sqrtSnn~=~5.02$ \TeV as a function of the number of participating nucleons~. The transverse area is calculated as the total area of overlap between participating nucleons using Eq.~\ref{eq:eps_lb}. The open circles are from \PbPb{} collisions at $\sqrtSnn~=~2.76$~\TeV and calculated via direct measurements of $\ET$~. A fit to a power law $a\Npart^p$ is shown with best-fit parameter values $a=0.8\pm0.2$ and $p=0.44\pm0.07$, and $\chi^2/dof~=~1.2/16$.