Measurements of $\langle $d$E_{\mathrm T}/$d$\eta \rangle / \langle N_{\mathrm{quark}}/2 \rangle$ versus $\langle N_{\mathrm{part}} \rangle$ at midrapidity in Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV. Note the suppressed zero. The boxes indicate the systematic uncertainties.