Specific energy loss (d$E$/d$x$) vs. rigidity (momentum/charge) for TPC tracks from pp collisions at $\sqrt{s}$ = 7 TeV (top panel) and from 0-80% most central Pb-Pb collisions at $\snn$ = 2.76 TeV (bottom panel). The solid lines represent a parametrization of the Bethe-Bloch curve.