Correlation functions of \spipi pairs in bins of \kt for $1\leq N_{\mathrm{ch}} \leq 18$, the fits are performed using CATS  employing the RSM. The left (right) panels show the results assuming a polynomial of first (second) degree as background. The uncertainties of the data points are obtained by varying the selection criteria as described in the text. The uncertainty bands of the fit function are obtained by employing a bootstrap  procedure.