# Figure 2

 Invariant-mass distributions of KK pairs for pp and the 0-5$\%$ most central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV for the momentum ranges 0.5 < $p_{\mathrm{T}}$ < 0.8 GeV/$c$ (upper panel) and 10 < $p_{\mathrm{T}}$ < 13 GeV/$c$ (lower panel), respectively. In panels (a) and (c) the unlike charge KK invariant-mass distribution from the same event and normalized mixed event background are shown. In panels (b) and (d) the invariant-mass distribution after subtraction of the combinatorial background for $\phi$ is shown. The statistical uncertainties are shown by bars. The solid curves are the fits to the distributions and the red dashed curves are the components of those fits that describe the residual background.