Comparison of the correlation functions for $\pi^{+}\pi^{-}$ pairs at $\sqrt{s} = 7 $TeV (closed symbols) to the PYTHIA MC simulations (open symbols), in selected multiplicity and $k_{\rm T}$ intervals. The plot is made as a function of $q_{inv}$ instead of $q_{LCMS}$ so that the resonance peaks are better visible