Speaker
Antoine Lardeux
(CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))
Description
Heavy quarkonium states are expected to provide essential information on the properties of the deconfined state of nuclear matter, the Quark-Gluon Plasma (QGP), formed in the early stages of ultra-relativistic heavy-ion collisions.
In particular, the suppression of the strongly bound quarkonium states via the color screening mechanism can be seen as an effect of deconfinement.
Furthermore, a weaker suppression is foreseen going from mid- to forward rapidity due to the decrease of the medium energy density.
ALICE results on charmonium suppression in Pb-Pb collisions seem to indicate that additional mechanisms as $J/\psi$ production via recombination of charm and anti-charm quarks also play a role, leading to a more complex picture of the quarkonium melting in the QGP.
This so-called regeneration mechanism is expected to be small for bottomonia due to the smaller number of initial $b\bar{b}$ pairs produced compared to $c\bar{c}$ pairs.
In ALICE, $\Upsilon$ are measured down to zero transverse momentum via the dimuon decay channel in the Forward Muon Spectrometer ($2.5 < y < 4$).
After a brief description of the apparatus, we will report on the $\Upsilon$ nuclear modification factor in p-Pb collisions at $\sqrt{s_{_{\rm NN}}}= 5.02$ TeV and in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}}=2.76$ and $5.02$ TeV.
Finally, comparisons with other experimental measurements as well as with theoretical calculations will be discussed.
| On behalf of collaboration: | ALICE |
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Author
Antoine Lardeux
(CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))
