Example invariant-mass distributions for the $\rm K^{*0}$ in the 0-20% centrality interval in two $\pt$ ranges: $0.8< \pt< 1.2$ GeV/$c$ [panels (a) and (b)] and $2.5< \pt< 3$ GeV/$c$ [panels (c) and (d)]. Panels (a) and (c) show the unlike-charge invariant-mass distributions for $\rm K^{*0}$ with combinatorial backgrounds. The normalized mixed-event combinatorial background is within 0.5% (0.7%) of the unlike-charge distribution for the low (high) $\pt$ bin over the invariant-mass range shown here. The statistical uncertainties are not visible given the vertical scale. Panels (b) and (d) show the invariant-mass distributions after subtraction of the mixed-event background (plotted with statistical uncertainties) with fits to describe the peaks of the $\rm K^{*0}$ (solid curves) and residual backgrounds (dashed curves). In the interval $0.8< \pt< 1.2$ GeV/$c$ ($2.5< \pt< 3$ GeV/$c$ ), the uncorrected $\rm K^{*0}$ yield is 7.4 (2.4) million, or 2.4 (0.80) per event; the signal-to-background ratio is $1.1\times10^{-4}$ ($5.6\times10^{-4}$) and the significance of the $\rm K^{*0}$ peak is 17 (25). | |