Excited charmonium suppression in proton-nucleus collisions as a consequence of comovers

Abstract

Recent results from proton(deuteron)-nucleus collisions at RHIC and LHC energies have shown an unexpected suppression of excited quarkonium states as compared to their ground states. In particular, stronger suppression of the $\psi(2S)$ relative to the $J/\psi$ has been detected. Similar observations were made at lower energies and were easily explained by nuclear absorption. At higher energies, a similar explanation would violate the Heisenberg principle, since the calculations based on the uncertainty principle lead to a charmonium formation time expected to be larger than the nuclear radius, which results in identical nuclear break-up probability for the $\psi(2S)$ and $J/\psi$. On the contrary, this behavior is naturally explained by the interactions of the quarkonium states with a comoving medium. We present our results on $J/\psi$ and $\psi(2S)$ production for d+Au collisions at $\sqrt{s}=200$ GeV and for p+Pb collisions at $\sqrt{s}=5.02$ TeV.