Heavy quarkonia perspectives with heavy-ions in ALICE
E. VercellinUniversità and INFN Torino – Italy
For the ALICE collaboration
ALICE Set-up
HMPID
Muon Arm
TRD
PHOS
PMDITS
TOF
TPC
Size: 16 x 26 metersWeight: 10,000 tons
Quarkonia detection in ALICE• Performed both in the
– dielectron channel (central barrel, key-detector: TRD) – dimuon channel ( forward rapidity region, Muon Spectrometer)
• Complementary features and performance
Quarkonia Acceptance – dimuon channel
-J/: pt,cut= 1 GeV/c
Dimuon trigger: pt cut on individual muons to reject combinatorial background
: : pt,cut= 2 GeV/c
Quarkonia acceptance – dielectron channel
Dielectron trigger: pt cut of 3 GeV/c on individual electrons.
Not always needed (e.g. Pb-Pb central).
Running conditions at Point 2
Collision system √sNN(TeV) L0 (cm-2s-1) Run time (s/year)
geom (b)
pp 14.0 1031 * 107 0.07
PbPb 5.5 1027 106 ** 7.7
pPb 8.8 1029 106 1.9
ArAr 6.3 1029 106 2.7
*Lmax = 1034 ** Lint (ALICE) ~ 0.5 nb-1/year
+ other ions (Sn, Kr, O) & energies (e.g.: pp @ 5.5 TeV)
Simulation inputs
• Quarkonia:– X-sect from Color Evaporation
Model– Pt distribution extrapolated
from CDF data– Feed-down from higher– resonances included– J/ from B decay included– Shadowing (EKS)
• Open heavy flavors– X-sect and kinematic
distributions from NLO pQCD (NMR)
– PYTHIA tuned to NLO for event generation
– Shadowing (EKS) /k : Hijing
For more details see PPR Vol. II – J. Phys. G. Nucl. Part. Phys. 32 (2006)
Quarkonia to dielectrons: Pb-PbDielectron invariant mass spectrum in central collisions after one “ALICE-year” of Pb-Pb data taking
Quarkonia to dielectrons: Pb-Pb
Dielectron invariant mass spectrum in top 10% central collisions after one “ALICE-year” of Pb-Pb data taking
Zoom in the J/ region
Zoom in the region
Quarkonia to dielectrons: p-p
Quarkonia to dimuons: Pb-Pb
Statistics for 0.5 nb-1
-J/: excellent (670.000)- ’: marginal - Y: ok (7000)- Y’: low (2000)- Y’’: very low (1000)
Normalization on open bB -> J/ + X
Quarkonia +-: suppression studies in Pb-Pb
Statistical errors corresponding to one month run.Hp : “perfect” subtraction of comb. background Hp. Nucl. Absorpt. cross sect. = 0 (hint from RHIC)
Shadowing + two QGP suppression scenarii: low vs. high diss. temperature
Centrality dependence of J/ and yields normalized to open beauty
Quarkonia +-: suppression studies in Pb-Pb Centrality dependence of ’ / J/ and ’/ ratiosSame working hypothesis as previous slide
J/, Y, Y’: Excellent sensitivity to different suppression scenariosY’’: Needs 2-3 years of high luminosity’:Will be very difficult
Quarkonia to dimuons: pp coll. at 14 TeV Statistics expected in a pp run of 107s at L=31030 cm-2s-1
2.8 106 J/ 2.7 104
Invariant mass resolution at the J/ peak: ~ 70 MeV/c2
Invariant mass resolution at the peak: ~ 100 MeV/c2
Quarkonia to dimuons in pp collisions at 14 TeV: study of pt and y distributions
pt distribution: test of prod.
mechanisms (see Tevatron)
J/ rapidity distribution: sensitivity to gluon distributions at low x ?
(statistics for one pp run : 107s at L=31030 cm-2s-1)
Quarkonia polarization is reconstructed from the angular distribution of the decay products (J/ +- ) in the quarkonia rest frame
θcos α1cosθ ddσ 2
Measurement of quarkonia polarization in pp collisions
y
z
x
H+
pproj ptarg
J/ -
=+1
=-1
Transverse polarization
Longitudinal polarization
With the foreseen pp statistics the measurement of J/ polarization isfeasible in ALICE, also as a function of pT
Conclusions
• Quarkonia production studied in Alice both in the dielectron and dimuon channels
• The two methods are complementary under different points of view.
• Quarkonia detected over a wide rapidity range from -4 till +0.9
• Thanks to ALICE characteristics, quarkonia will be studied together with all known observables for heavy ion collisions
• Measurements in p-p collisions are a relevant part of the ALICE program