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.