Left: Single-kaon purity as a function of particle momentum $p$ for 0-10%, 10-30%, and 30-50% centrality intervals. Points are shifted along the $x$ axis for clarity. Right: K$^+$K$^-$ pair purity as a function of pair transverse momentum $k_{\rm T}$. Systematic uncertainties are shown by bars. Statistical uncertainties are smaller than the size of the markers.