The double ratio between the $\psi(\rm 2S)$ and \jpsi cross sections in \pPb and pp collisions at $\snn=5.02$ and 8.16 TeV , shown as a function of $\langle N_{\rm coll}\rangle$ for the backward (Pb-going) rapidity region and compared to the comover model results . The boxes around unitycorrespond to the global systematic uncertainty on the ratio between the $\psi(\rm 2S)$ and \jpsi cross sections in pp collisions.