Fr

1
Charmonia production in heavy ion collisions,
from SPS to LHC

• Frédéric Fleuret
• LLR CNRS/IN2P3
• École polytechnique
• Palaiseau, France

2
Introduction

• Motivations
• Suppression of quarkonia is a prediction of
  lattice QCD calculations, for instance
• Experimental setup
• SPS/CERN NA38, NA50 and NA60 experiments (?sNN
  17 30 GeV)
• Fixed target experiments
• Statistic 100 000s J/y
• Data sets pA w/ Ap, d, Be, Al, Cu, Ag, W, Pb
  SU, InIn, PbPb
• Small rapidity coverage (typically y ? 0,1)
• RHIC/BNL Phenix experiment (?sNN 200 GeV)
• Collider experiments
• Statistic 1000s J/y (10000s since 2007)
• Data sets pp, dAu, CuCu, AuAu)
• Large rapidity coverage (y ? -0.5,0.5, y ?
  -2.2,-1.2 and y ? 1.2,2.2)

H. Satz, J. Phys. G 32 (2005)
3
Charmonium production at SPS

• NA38, NA51, NA50,NA60
• Two major results
• Observation of Cold Nuclear Matter effects
  Absorption by nuclear matter
• Suppression observed from pp to peripheral PbPb
  
• J/y survival probability
• Fit to data sabs4.18 ?0.35 mb
• Observation of Anomalous suppression in PbPb
  (NA50) and InIn (NA60) central collisions when
  compared with Cold Nuclear Matter effects.

J/y normal nuclear absorption curve
L

• NA50, EPJ C39 (2005) 335
• NA60, PRL99 (2007) 132302

central
peripheral
mid
J/y
collisions
4
Charmonium production at RHIC
Npart number of participant nucleons

• PHENIX
• Two experimental stricking observations
• Point 1 similar behavior SPS.vs.RHIC at
  mid-rapidity
• At a given Npart, expect different energy
  densities
• Dont expect same CNM effects

If no nuclear effet, RAA 1
PHENIX, PRL98 (2007) 232301
central
peripheral
mid
collisions
5
Charmonium production at RHIC
Npart number of participant nucleons

• PHENIX
• Two experimental stricking observations
• Point 1 similar behavior SPS.vs.RHIC at
  mid-rapidity
• Point 2 larger suppression at forward rapidity
  compared to mid-rapidity (confirmed with recent
  data)

PHENIX, PRL98 (2007) 232301 PHENIX preliminary
central
peripheral
mid
collisions
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SPS .vs. RHIC at mid-rapidityCold Nuclear Matter
effects
PHENIX, PRC77 (2008) 024912

• Measured RAA include
• Hot and Dense Matter effects (HDM)
• Cold Nuclear Matter effects (CNM)
• Need to remove CNM effects
• At SPS use pA data (sabs 4.2 mb)
• At RHIC use dAu data
• Shadowing (modification of PDFs) could play a
  role
• Absorption can be smaller
• due to large uncertainties in dAu data at RHIC
  cant tell weither CNM effects are the same or
  not.
• Need more precise CNM effect measurements at RHIC
  
• run 8 30 x more data (ongoing analysis)

sabs 4.2 mb
dAu
AuAu
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SPS .vs. RHIC and RHIC mid.vs.fwdHot and Dense
Matter effects suppression models

• suppression models which reproduce SPS data
  overestimate the suppression at RHIC

All models for y0
SPS
RHIC

• Fwd.vs.mid in comovers model
• Comovers density is larger at mid-rapidity
  ? larger suppression expected at mid-rapidity
• Fails to reproduce the data

Phys. Rev. C76, 064906 (2007)
8
RHIC mid.vs.fwdHot and Dense Matter effects
recombination

• recombination models
• Recombination (regeneration) is a mechanism which
  leads non-correlated c and c quarks to combine
  into a cc bound state (such as J/y) cc ? J/y
  X
• Compensate direct suppression

J. Phys. G 34 (2007) S749

• Recombination .vs. Rapidity
• Adding recombination to comovers
• More recombination at mid-rapidity

How to test recombination ?
arXiv0712.4331v1
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Testing recombinationPHENIX J/Y flow measurement
Non photonic electrons

• Non photonic electrons (charmbeauty) flow at
  RHIC. If J/y are regenerated, they should inherit
  from charm-quark flow.
• Current measurements are not precise enough to
  discriminate.

The elliptic flow v2 characterizes the azimuthal
anisotropy of particle emission with respect to
the collision reaction plane
Positive v2 ? thermalization of the medium
J/y AuAu v2 for y ? 1.2,2.2 J/y AuAu v2
for y lt 0.35
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RHIC mid.vs.fwdback to CNM effects

• Could the difference mid.vs.fwd come from CNM
  effects ?
• CGC (gluon saturation)
• Enhancement of 3 gluons fusion in J/Y production
  mechanism
• Absolute amount of suppression is fitted on
  semi-peripheral data
• Ratio fwd/mid comes from the model

arXiv0808.2954

• Shadowing (modification of PDFs) based on new
  gg ?J/yg calculations

AuAu
dAu
extrinsic gg ? J/y g X
dAu
intrinsic gg ? J/y X
AuAu
arXiv0809.4684
arXiv0809.4684
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Point 2 RHiC mid.vs.fwdback to the data

• Extrapolate CNM effects from dAu to AuAu with
  data driven method
• Fit dAu data as a function of centrality (impact
  parameter)
• Extrapolate to AuAu
• Within errors, the suppression could be the same
  at forward and mid rapidity
• Need better statistics in dAu ? run 8 (2008) dAu

Survival 38 1822
Mid rapidity
Forward rapidity
Survival 55 2338
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Conclusionfor SPS and RHIC

• Summary of SPS and RHIC
• Comparable RAA at mid-rapidity between SPS and
  RHIC
• Larger suppression observed by PHENIX at forward
  rapidity compared to mid rapidity ? several
  explanations not discriminate yet.
• CNM effects are not well constrained at RHIC.
  Need better measurement ? run 8 dAu data ( 80
  000 J/Y) may need other systems.
• Next at RHIC
• RHIC luminosities advance
• Detector upgrades
• PHENIX barrel and endcap silicon vertex
  detector
• STAR DAQ upgrade tracking upgrade (silicon
  pixel sensors silicon strip pad sensors)
• Impact on physics
• Better mass resolution, better signal/background
  ratio
• Y, cc measurements (J/Y 0.6 J/Y 0.3 cc ?
  J/Y 0.1 Y?J/Y) ?

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Outlookfor LHC

• ATLAS
• Large rapidity acceptance y lt 2.5
• Good mass resolution (s68 MeV/c²)
• Signal/bkg 1
• Difficult to reconstruct ms with pTlt2.5 GeV

• CMS
• Large rapidity acceptance n lt 2.4
• Very good mass resolution (s35 MeV/c²)
• Signal/bkg 0.6
• Limited acceptance at low pT

J. Phys. G Nucl. Part. Phys. 34 (2007) 2307-2455
A. Lebedev - QM08
One month PbPb (0.5 nb-1)
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Outlookfor LHC

• ALICE mid (ee-)
• J/? ? dielectron (ylt0.9)
• Resolution s30 MeV/c²
• Signal/Bkg 1.2
• Expected rate (one month, 106s) 120k

• ALICE forward (mm-)
• J/y ? dimuon (-4ltylt-2.5)
• Resolution s70 MeV/c²
• Signal/bkg 0.2
• Expected rate (one month) 680k

J. Phys. G Nucl. Part. Phys. 32 (2006) 12952040
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Outlookupsilon

• In the future, new observable bottonium states
• Expected rates

STAR 12 weeks AuAu
PHENIX 12 weeks AuAu
LHC 1 month
ALICE 2m
ALICE 2e
CMS 2m
ATLAS 2m
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Charmonia production in HICconclusion

• Many results already got from SPS and RHIC
• Still difficult to get a satisfying overall
  picture
• Lack of CNM effects understanding at RHIC (so
  far)
• New results from RHIC and upgrades should help to
  make progress
• Larger statistic (AuAu 2007, dAu 2008 and
  futur)
• Better heavy flavor study (thanks to upgrades)
• Y and cc ?
• LHC experiments should provide a complementary
  view
• Much higher energy (from 5.5 TeV in PbPb to 14
  TeV in pp) and high statictics
• Very good detector performances
• But
• Only one month of Heavy Ion Collisions per year
• Different energy regimes (constant Z/AEnergy)
• pp _at_ 14 TeV (can do pp _at_ 5.5 TeV, but taken on
  HIC one month program)
• PbPb _at_ 5.5 TeV
• pPb or Pbp _at_ 8.8 TeV (ALICE has (only) one muon
  spectrometer)
• Asymetric beam energy implies shift of rapidity
  window (0.5 unit for pPb compared to PbPb) ?
  issues for CNM effects