$\pt$-differential cross section of electrons from heavy-flavor hadron decays compared to pQCD calculations from FONLL (red), GM-VFNS (blue) and $k_{{\rm T}}$-factorization (green). Uncertainties on the theory calculations originate from the variation of the factorization and the renormalization scales and from the heavy-quark masses. The ratios data/theory are shown in the lower panels, where the dashed lines indicate the additional theoretical uncertainties relative to unity.