exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

Fig 2 : Fit of the J/ invariant mass spectra in the
p T range from 3 to 4 GeV/c in p-p collisions at 7
TeV.
This study continues now with the J/ , which can
be measure down to zero p T where CGC effects
would appear more dramatically.
The study of the J/ in p-p collisions is also of a
first importance as a reference measurement for
the p-Pb and Pb-Pb collisions [9,10]. The IPNO
ALICE team is involved in the extraction of the J/
cross section at LHC energies. This study constitutes
the main subject of a new PhD (started in
October 2008). In this thesis we study the different
fitting methods and the corrections to apply in order
to calculate the cross-section (Fig 2 and 3) for
different p T ranges. We also study the impact of
Fig 3 : J/ acceptance and efficency map in y and
p T range for the muon spectrometer in p-p
collisions at 7 TeV.
the number of collected J/ on the result uncertainties.
This work is directly linked to the one of the
Paper Preparation Group dedicated to the J/
study in p-p collisions. The deputy convener for
this first paper belongs to our group.
The last physics theme about the J/ concerns its
expected suppression in Pb-Pb collisions relatively
to p-p collisions. One of the main problem in this
study is to separate the contribution of the different
J/ production sources. An important part (~ 20%)
comes from the B decay meson. Contrary to the
ALICE central part, the muon spectrometer is unable
to directly separate this contribution because
there is not a forward silicon tracker to see the
shifted B decay vertices. A possibility to measure
indirectly this contribution in the muon spectrometer
is to study 3 muons events. For example a B
meson giving a J/ plus another meson, all of
them decaying into muons. This kind of measurement
would be a complementary one to that of the
ALICE central barrel where B mesons will be extracted
thanks to the high resolution silicon tracker
able to measure shifted B decay vertexes. ALICE
upgrades program include the possibility to add a
forward silicon tracker to enable such measurement
in the muon spectrometer.
With the startup of the LHC, the ALICE collaboration
has demonstrated is capacity to extract the
physics results from the collected data very
quickly. The two forthcoming years will be rich of
new results which will shed a new light on quarkonia
physics.
References
[1] First proton-proton collisions at the LHC as
observed with the ALICE detector: measurement
of the charged particle pseudorapidity
density at sqrt(s) = 900 GeV – Eur. Phys. J.
C 65 1-2 (2010) 111-125
[2] Heavy Ion Physics with ALICE -
arXiv:0907.0577 – Proceeding Bormio 2009
[3] Little Bang avec ALICE – Published in Plein-
Sud spéciale recherche 2008-09
[4] Numerical Simulations and Online Reconstruction
of the Muon Spectrometer of AL-
ICE - ALICE-INT-2009-044
[5] Low-x QCD at the LHC with the ALICE detector
- Acta Physica Polonica B, vol2, N° 2,
2009 and also on arXiv:0911.1458 -
[6] The Color Glass Condensate framework in
p+p and p+A interactions at the ALICE experiment
– proceeding SQM09 submitted to
Journal of Physics G : Nuclear and Particle
Physics
[7] Heavy Quark production in the Color Glass
Condensate framework: proton-proton and
proton-nucleus collision studies in the ALICE
Dimuon Forward Spectrometer - ALICE-INT-
2009-043
[8] Étude de la production de saveurs lourdes
et de la multiplicité de particules chargées
dans le cadre du formalisme du Color Glass
Condensate pour les collisions p+p et p+Pb
dans l'expérience ALICE au LHC - Magdalena
Malek PhD – IPNO-T-09-03
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