Speaker
Gines Martinez-Garcia
(Centre National de la Recherche Scientifique (FR))
Description
We report on the first measurement of an excess in the yield of J/psi at
very low transverse momentum with respect to expectations from hadronic
production, performed by ALICE at the LHC in Pb-Pb collisions at 2.76 TeV.
Remarkably, the measured nuclear modification factor of J/$\psi$ in the
rapidity range 2.5<$y$<4.0 reaches about 7 (2) for Pb-Pb collisions in
the $p_\mathrm{T}$ range 0-300 MeV/$c$ and in the 70--90% (50--70%) centrality class.
The excess is observed at very low $p_\mathrm{T}$, below 300 MeV/c, evoking the $p_\mathrm{T}$
distribution of J/$\psi$ coherent photoproduction measured in ultra
peripheral Pb-Pb collisions.
The J/$\psi$ production cross section associated with the observed
enhancement in the yield is obtained under the hypothesis that coherent
photoproduction is the underlying physics mechanism.
If this hypothesis is confirmed, the observation of J/$\psi$ coherent
photo-production in Pb-Pb collisions at impact parameters smaller than
twice the nuclear radius opens new theoretical and experimental
challenges. Furthermore, such a new quarkonium production mechanism
could become a novel probe of the QGP at LHC energies.
| On behalf of collaboration: | ALICE |
|---|
Author
Gines Martinez-Garcia
(Centre National de la Recherche Scientifique (FR))
