Speaker
Roberta Arnaldi
(Universita e INFN (IT))
Description
Charmonium states play a relevant role as probes of the phase transition
between hadronic and deconfined matter. According to the color-screening model,
the in-medium dissociation probability of such states should provide an estimate
of the initial temperature.
In nucleus-nucleus collisions, the more loosely bound excited states, as the $\psi(2{\rm S})$,
are expected to melt at lower temperatures than the ground state (J/$\psi$).
In proton-nucleus collisions at LHC energies, the charmonium formation time is larger than the
time spent by the ccbar pair traversing the nucleus. Therefore, the cold nuclear matter
is expected to affect in a rather similar way the J/$\psi$ and $\psi(2{\rm S})$.
ALICE results on the inclusive $\psi(2{\rm S})$ production at forward rapidities ($2.5 < y < 4$), will
be presented. Final results on the $\psi(2{\rm S})$/J/$\psi$ ratio in Pb-Pb collisions at
$\sqrt{s_{\rm NN}} = 2.76$ TeV will be shown and compared to the corresponding pp measurement.
Results on the $\psi(2{\rm S})$ production in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV
will be also discussed. We observe an unexpected suppression of the $\psi(2{\rm S})$ yield, with respect to
the J/$\psi$ one, which is difficult to reconcile with the presence of cold nuclear matter effects alone.
To provide further insight on this observation, a differential study of the
$\psi(2{\rm S})$ suppression, as a function of transverse momentum and
centrality will be presented. Finally, ALICE $\psi(2{\rm S})$ results will be compared with theoretical models
and with results by other experiments.
| On behalf of collaboration: | ALICE |
|---|
Primary author
Roberta Arnaldi
(Universita e INFN (IT))
