Invariant-mass distributions of \kk pairs for the 0--10\% and 70--80\% centrality classes in \PbPb collisions at \snn $=$ 5.02 \TeV for the transverse momentum ranges 0.8 \textless \pt \textless 1.0 \GeVc. The left panels show the unlike charge \kk invariant-mass distribution from the same event and the normalized mixed event background. The right panels report the invariant-mass distribution after subtraction of the combinatorial background for \phim. The solid curves represent fits to the distributions and the dashed curves are the components of the fits that describe the residual background. The statistical uncertainties are shown by bars.