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

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.Comment: 7 pages, 5 figures. Extended version, figures unchanged. Accepted for publication in Physics Letters

Correlations at RHIC and the Clustering of Color Sources

We present our results on transverse momentum fluctuations and multiplicity fluctuations in the framework of the clustering of color sources. In this approach, elementary color sources -strings- overlap forming clusters, so the number of effective sources is modified. These clusters decay into particles with mean transverse momentum that depends on the number of elementary sources that conform each cluster and the area occupied by the cluster. We find a non-monotonic dependence of the $p_T$ and multiplicity fluctuations with the number of participants. In our approach, the physical mechanism responsible of these fluctuations is the same: the formation of clusters of strings that introduces correlations between the produced particles.Comment: 3 pages, 1 figure, proceedings of Quark Confinement and Hadron Spectrum VII, Ponta Delgada, Portugal, 2-7 September 200

Charmonium dissociation and recombination at LHC: Revisiting comovers

We present our results on charmonium production at the Large Hadron Collider energies within the comover interaction model. The formalism includes both comover dissociation of $J/\psi$'s and possible secondary $J/\psi$ production through recombination. The estimation of this effect is made without involving free parameters. The comover interaction model also incorporates an analytic treatment of initial-state nuclear shadowing. With these tools, the model successfully describes the centrality, transverse momentum and rapidity dependence of the experimental data from PbPb collisions at the LHC energy of $\sqrt{s} = 2.76$ TeV. We present predictions for PbPb collisions at $\sqrt{s} = 5.5$ TeV.Comment: Review and updated version to conform with published version.Several clarifying comments added, results unchanged. 17 pages, 12 figure