1. Andry Rakotozafindrabe LLR – École Polytechnique
J/ production in Cu+Cu and Au+Au collisions at √sNN = 200 GeV measured by PHENIX at RHIC
Andry Rakotozafindrabe
LLR – École Polytechnique
42nd Rencontres de Moriond
QCD session – Italy (March 2007)

2. Physics motivation – the starting point
What are the properties of the hot and dense matter produced in relativistic heavy ion collisions ?
c and b are produced in the initial parton collisions, so they can be used to probe the created medium :
open charm (or beauty) energy loss  energy density
Topic already covered this morning by Alan Dion
, (quarkonia) suppressed by color screening  deconfinement
At lower energy, NA50 (CERN) experiment measured an anomalous J/ suppression in Pb+Pb collisions, in excess of the normal suppression expected from the nuclear absorption.
NA50 Collaboration, Eur. Phys. J. C39 (2005) 335
At lower energy, NA60 (CERN) recent results in In+In
At RHIC energy ?
10x √sNN
2-3x gluon density
23/03/2007
Andry Rakotozafindrabe – LLR

3. Screening the J/ in a QGP
Production
~ 60% direct production J/
~ 30% via χc J/ + x
~ 10% via ’ J/ + x
Temperature of dissociation Td
for χc and ’: Td ~ 1.1 Tc
for J/ : Td ~ 1.5 to 2 Tc
Sequential dissociation as the temperature (or energy density) increases :
Satz, J.Phys.G32:R25,2006 ’ χc
J/
Energy density (τ0 = 1fm) vs the max. √s for SPS, RHIC and LHC
23/03/2007
Andry Rakotozafindrabe – LLR

4. Physics motivation – a few complications
J/ or 
+ feed-down b, ’, c J/ + x
quarkonia production
g+g fusion dominant at RHIC energies
Final state
“Normal” nuclear absorption
Absorption by (hadronic ?) comovers ?
Color screening ?
In-medium formation (recombination) ?
Flow ?
Sensitive to:
Initial state
Modification of the parton distribution functions (shadowing, CGC)
pT broadening (Cronin effect)
Parton energy loss in the initial state ?
23/03/2007
Andry Rakotozafindrabe – LLR

5. J/ in PHENIX : capsule history
Run Species √s [GeV ] Ldt # J/ # J/ Reference
|y|< <|y|<2.2
Au+Au b-1
02 Au+Au b PRC69, (2004)
p+p pb PRL92, (2004)
d+Au nb PRL96, (2006) p+p pb
Au+Au b nucl-ex/
Au+Au b-1
05 Cu+Cu nb coming soon
Cu+Cu nb
Cu+Cu b-1
p+p pb hep- ex/
06 p+p pb-1
p+p pb-1
23/03/2007
Andry Rakotozafindrabe – LLR

6. Andry Rakotozafindrabe – LLR
PHENIX detector
J/  e+e–
|y| < 0.35
Pe > 0.2 GeV/c
 = 
Tracking, momentum measurement with drift chambers, pixel pad chambers
e ID with EmCAL + RICH
J/µ+µ–
1.2< |y| < 2.2
Pµ > 2 GeV/c
 = 2
Tracking, momentum measurement with cathode strip chambers
µ ID with penetration depth / momentum match
Centrality measurement, vertex position
Beam-beam counters (charged particle production) Zero-degree calorimeters (spectator neutrons)
23/03/2007
Andry Rakotozafindrabe – LLR

7. Production baseline : (Run5) p+pJ/ @ √s = 200 GeV
energy
rapidity
Cross section vs : pT
hep-ex/
Cross section vs rapidity better constraints on available J/ production mechanisms
Total cross section in p+p
Bll.pp(J/ ) = 178 ± 3(stat)
± 53(sys) ± 18(norm) nb
in agreement with COM
Cross section vs pT
Forward rapidity
<pT2> = 3.59 ± 0.06 ± 0.16
Central rapidity
p+pJ/ measurement used as a reference for A+BJ/ :
23/03/2007
Andry Rakotozafindrabe – LLR

8. Heavy ion results @ √s = 200 GeV
Au+Au final results : nucl-ex/
Cu+Cu preliminary results (QM05)
but forthcoming final results (article in preparation) with
increased statistics in the dielectron channel (a factor ~2)
significant improvement of systematic errors
better precision measurement than the present Au+Au results for Npart<~100 1
RAA
Bar: uncorrelated error
Bracket : correlated error
23/03/2007
Andry Rakotozafindrabe – LLR

9. RHIC : beyond cold nuclear matter effects
Available d+Au data
qCNM :
Weak shadowing and weak nuclear absorption (σabs ~ 1mb favored) derived from model Vogt PRC71, (2005)
Au+Au data : even compared to the « worst » σabs~ 2mb case shown here
suppression beyond cold effects for
Npart>100 at y~1.7
Npart>200 at y~0
Need to improve the knowledge of CNM effects at RHIC
Bar: uncorrelated error
Bracket : correlated error
nucl-ex/
RHIC CNM effects :
σ abs = 0, 1, 2 y=0, y=2
Cold nuclear matter predictions from Vogt, nucl-th/ (shadowing + σabs)
23/03/2007
Andry Rakotozafindrabe – LLR

10. RHIC : different amount of suppression at different rapidities
nucl-ex/
RAA vs Npart :
Stronger suppression at forward rapidity than at central rapidity
Ratio forward/central ~0.6 for Npart>100
CGC (initial state effect) ?
models predicts less heavy quark production at forward rapidity than at mid rapidity
K. L. Tuchin J.Phys. G30 (2004) S1167
ratio RAA (1.2<|y|<2.2) /RAA (|y|<0.35) 1
RAA
Bar: uncorrelated error
Bracket : correlated error
23/03/2007
Andry Rakotozafindrabe – LLR

11. Andry Rakotozafindrabe – LLR
RHIC vs SPS
0<y<1 :
√s ~ 17 GeV
CNM = normal nuclear absorption σabs = 4.18 ± 0.35 mb
Maximum ε ~ 3 GeV/fm3 (τ0 = 1)
Compare to |y|<0.35 :
x10 √s
CNM = shadowing + nuclear absorption σabs from 0 to 2mb (Vogt, nucl-th/ )
Maximum ε ~ 5 GeV/fm3 (τ0 = 1), higher than at SPS
Same pattern of J/ suppression for the same rapidity!
Suppression beyond CNM larger at RHIC
NA50 at SPS (0<y<1)
PHENIX at RHIC (|y|<0.35)
PHENIX at RHIC (1.2<|y|<2.2)
Bar: uncorrelated error
Bracket : correlated error
Global error = 12% is not shown
23/03/2007
Andry Rakotozafindrabe – LLR

12. RHIC vs SPS (II) : extrapolating suppression models
Suppression models in agreement with NA50 data extrapolated at RHIC energies
Opposite suppression behaviour vs rapidity
Unmatched suppression pattern at central rapidity
Recombination at work at RHIC ?
Dissociation by thermal gluons
(R. Rapp et al., nucl-th/
Nu Xu et al., Phys.Rev.Lett. 97 (2006) )
Dissociation by comovers
(Capella et al., hep-ph/ )
23/03/2007
Andry Rakotozafindrabe – LLR

13. Recombination at RHIC ?
Suppression+recombination predictions compared to data
RAA vs Npart
R. Rapp et al. PRL 92, (2004)
Thews Eur. Phys. J C43, 97 (2005)
Nu Xu et al. Phys.Rev.Lett. 97 (2006)
Bratkovskaya et al. PRC 69, (2004)
A. Andronic et al. nucl-th/
Better matching with the data
but regeneration goes as the (single) charm density which is poorly known at RHIC
What about the other variables ?
23/03/2007
Andry Rakotozafindrabe – LLR

14. Recombination at RHIC ?
Suppression+recombination predictions compared to data
RAA vs Npart
Yield vs rapidity
RMS 1.32±0.06
RMS 1.30±0.05
Recombination predicts a narrower rapidity distribution with an increasing Npart
Data shows a slight decrease of the RMS with increasing centrality
Thews & Mangano, PRC73 (2006) c
No recombination
All recombination
RMS 1.40±0.04
RMS 1.43±0.04
nucl-ex/
23/03/2007
Andry Rakotozafindrabe – LLR

15. Recombination at RHIC ?
Suppression+recombination predictions compared to data
RAA vs Npart
Yield vs rapidity
<pT2> vs Ncoll
No recombination
Recombination predicts a narrower pT distribution with an increasing centrality, thus leading to a lower <pT²>
Data shows a rather flat dependence of <pT²> with centrality
With recombination
Thews, Eur.Phys.J. C43 (2005) 97,
Phys.Rev. C73 (2006)
(and private communication).
23/03/2007
Andry Rakotozafindrabe – LLR

16. Ending where it began: revisiting the sequential dissociation (I)
Karsch, Kharzeev & Satz, PLB 637 (2006) 75 :
Sequential melting  overall J/ survival probability (measured/expected):
S = 0.6 S direct J/  S J/←’, χc
Recent lattice QCD results : direct J/ melting at GeV/fm3
 S ~ 0.6 at RHIC
RAA/CNM vs.
Bjorken energy density
dET/dy : PHENIX, PRC 71, (2005)
Bar: uncorrelated error
Bracket : correlated error
PHENIX Global error = 12% + 7%
Box : uncertainty from CNM effects
εBj.τ0
Sequential dissociation of ψ’ and χc only does not seem to be consistent with the data
23/03/2007
Andry Rakotozafindrabe – LLR

17. Refinement : 3D hydro + sequential dissociation (II)
Gunji et al., hep-ph/ :
Charmonia
initial spatial distribution = from collisions in the Glauber model
+ free streaming in a full (3D+1) hydro
J/ survival probability ( RAA/CNM with CNM = shadowing + nuclear absorption σabs = 1mb )
S = (1 – fFD) S direct J/  + fFD S J/←’, χc
3 free parameters : feed-down fFD , melting temperatures TJ/ and T’,χc
+ (3D+1) hydro : same setup as the one used to reproduce charged dN/dη measured at RHIC
Assuming thermalization for τ°≥°0.6°fm, initial energy density distribution in the transverse plane, EOS of the medium (T<Tc and T>Tc), …
23/03/2007
Andry Rakotozafindrabe – LLR

18. Refinement : 3D hydro + sequential dissociation (II)
Gunji et al., hep-ph/ :
Charmonia
J/ survival probability ( RAA/CNM with CNM = shadowing + nuclear absorption σabs = 1mb )
S = (1 – fFD) S direct J/  + fFD S J/←’, χc
3 free parameters : Feed-down fFD , melting temperatures TJ/ and T’,χc
+ (3D+1) hydro
 best fit with :
TJ/ = 2.12 Tc
T’,χc = 1.34 Tc
fFD = 0.25
± 0.10 due to uncertainty
on σabs (1 ± 1mb)
Better matching with the data
23/03/2007
Andry Rakotozafindrabe – LLR

19. Andry Rakotozafindrabe – LLR
Summary (I)
PHENIX final results on J/dileptons at forward and mid-rapidity in p+p, Au+Au, and preliminary results in Cu+Cu :
Improved baseline
Run 5 p+p with x10 more statistics than Run 3
Suppression pattern
Beyond cold nuclear effects for Npart > 200
More suppression at forward than at central rapidity
Ratio forward/central ~0.6 for Npart>100
May be accounted for by CGC models
Suppression models (comover) predicts the opposite behaviour
Similar to SPS suppression in the same rapidity region? despite a higher energy density reached
Understandable as recombinations that partially compensate the J/ suppression ?
Still open question (test vs <pT²> dependance and rapidity distribution)
23/03/2007
Andry Rakotozafindrabe – LLR

20. Andry Rakotozafindrabe – LLR
Summary (II)
Alternate explanations ?
Sequential dissociation with feed-down assumed to be ~40% and direct J/ not melting at present energy densities is not consistent with data
(3D+1) hydro + sequential dissociation in agreement with mid-rapidity data if direct J/ is melting (at T = 2.12 Tc) and if feed-down is assumed to be (25 ± 10)%
Feed-down not measured at RHIC energies
At lower energies, large deviations between experiments
Need to improve knowledge on cold nuclear effects at RHIC
Stay tuned : forthcoming final results for Cu+Cu !
Improved precision for the measurements in the range Npart <~ 100
23/03/2007
Andry Rakotozafindrabe – LLR

21. Andry Rakotozafindrabe – LLR
Back-up
23/03/2007
Andry Rakotozafindrabe – LLR

22. Andry Rakotozafindrabe – LLR
Hint of things to come
Final results for Cu+Cu
What about the forward vs central suppression at lower Npart ? …
Improved reference p+p :
x3 higher statistics from run 6
Future measurements in ’ ?
Future measurements in χc
Planning Au+Au (1 nb-1 vs 0.24 nb-1 in run 4 ) with high luminosity during Run 7
Later runs : d+Au with higher luminosity (28 nb-1 vs 2.7 nb-1 in run 3) ?
Run 6 200GeV p+p
Invariant Mass (GeV/c2)
A. Bickley, Hard Probes 06
(c - J/) Mass (GeV/c2)
PHENIX
Run 5 200GeV p+p
Work under progress
23/03/2007
Andry Rakotozafindrabe – LLR

23. Upsilon measurement PHENIX QM05
Dimuon mass spectrum for the two muon arms added together.
y~1.7
~10 counts
PHENIX : 1st Upsilons at RHIC from ~3pb-1 collected during the 2005 p+p run.
y=0
~50 cnts
STAR QM06
STAR Preliminary
p+p 200 GeV
e+e- Minv
Background
Subtracted
23/03/2007
Andry Rakotozafindrabe – LLR

24. STAR results and near future
M. Cosentino, QWG06
STAR Preliminary
STAR – J/ Run4 AuAu
STAR – J/ Run5 pp
Dataset GeV :
No trigger due to high background
Just a faint signal
For efficient J/y trigger, full barrel ToF is needed (just patch in Run5)
(Run5):
trigger commissioning (~1.7M events)
Run 6: expect (work in progress)
Upsilon
23/03/2007
Andry Rakotozafindrabe – LLR

25. Andry Rakotozafindrabe – LLR
J/ production
Production
~ 60% direct production J/
~ 30% via χc J/ + x
~ 10% via ’ J/ + x
Large deviations between experiments : χc feed-down fraction vs √s
Not measured at RHIC energies
23/03/2007
Andry Rakotozafindrabe – LLR

26. Invariant yield vs tranverse momentum
23/03/2007
Andry Rakotozafindrabe – LLR

27. Andry Rakotozafindrabe – LLR
<pT2> vs Npart
A closer look at <pT2> vs Npart
hep-ex/ nucl-ex/
23/03/2007
Andry Rakotozafindrabe – LLR

28. Cold nuclear effects : d+AuJ/
Vogt, PRC71, (2005), Kopeliovich, NP A696, 669 (2001)
Phys. Rev. Lett. 96 (2006),
Low x2 ~ 0.003
(shadowing region)
Cold nuclear effects : d+AuJ/
gluons in Pb / gluons in p
Anti
Shadowing
Shadowing x
Nucl. Phys. A696 (2001)
Available d+Au data  CNM :
Weak shadowing (modification of gluon distribution) and weak nuclear absorption (σabs ~ 1mb favored) derived from model Vogt PRC71, (2005)
Data driven parametrizations of CNM
Karsch, Kharzeev & Satz, PLB 637 (2006) 75
Granier de Cassagnac, hep-ph/ xd
xAu
J/
South
y < 0
rapidity y
y < -1.2 : large xAu ~ 0.090 xd
xAu
J/
North
y > 0
y > 1.2 : low xAu ~ 0.003
y ~ 0 : intermediate xAu ~ 0.020
23/03/2007
Andry Rakotozafindrabe – LLR

29. RHIC : beyond cold nuclear effects (II) ?
Comparison to a data driven parametrization of CNM (Granier de Cassagnac, hep-ph/ ) in the same centrality classes
CNM : RAA(y, b) = Σcollisions[RdA(-y,b1i).RdA(+y,b2i)]/Ncoll
Essentially the same conclusions as the previous slide
But stat+syst error that comes from d+Au data are visible
Need a higher luminosity d+Au sample
23/03/2007
Andry Rakotozafindrabe – LLR

30. J/ production in d+Au vs centrality
High x2 ~ 0.09
Small centrality dependence
Model with absorption + shadowing ( black lines* ):
shadowing EKS98
σabs = 0 to 3 mb
σabs = 1 mb good agreement
σabs = 3 mb is an upper limit
weak shadowing and weak nuclear absorption
Low x2 ~ 0.003
*Colored lines: FGS shadowing for 3 mb
23/03/2007
Andry Rakotozafindrabe – LLR

31. SPS vs RHIC (III) : RAA/CNM vs Npart
NA50 at SPS (0<y<1)
PHENIX at RHIC (|y|<0.35)
PHENIX at RHIC (1.2<|y|<2.2)
0<y<1 :
CNM = normal nuclear absorption σabs = 4.18 ± 0.35 mb
Compare to |y|<0.35 :
CNM = shadowing + nuclear absorption σabs=1 mb (Vogt, nucl-th/ )
Additionnal syst. error from uncertainity on CNM
Need to improve knowledge on cold nuclear effects at RHIC
Suppression beyond CNM larger at RHIC
Bar: uncorrelated error
Bracket : correlated error
Global errors (12% and 7%)
are not shown here.
Box : uncertainty from CNM effect
23/03/2007
Andry Rakotozafindrabe – LLR

32. 100% Recombination (shape only)
Recombination at RHIC ?
RAA vs y
0mb
3mb
100% Recombination (shape only)
R. Vogt nucl-th/ (EKS)
R. L. Thews, M. L. Mangano Phys.Rev. C73 (2006)
23/03/2007
Andry Rakotozafindrabe – LLR

33. Andry Rakotozafindrabe – LLR
Charm flow
S. Sakai QM06
M. Djordjevic et al., Phys.Lett.B632 (2006) 81
dNg/dy=1000
c and b quark pT distributions at mid-rapidity before fragmentation : b contribution is dominant at high pT
Significant flow observed for heavy flavor electrons
Main source is D meson
(1) Consistent with c-quark thermalization
(2) large cross section is needed in AMPT ~10 mb
(3) Resonance state of D & B in sQGP
Charm quark strongly coupled to the matter
[Phys.Lett. B ]
[PRC72,024906]
[PRC73,034913]
23/03/2007
Andry Rakotozafindrabe – LLR

34. Computing the J/ yield
Invariant yield :
i : i-th bin (centrality for e.g.)
: number of ‘s reconstructed
: probability for a thrown and embeded
into real data to be found
(considering reconstruction and trigger efficiency)
: total number of events
: BBC trigger efficiency for events with a
: BBC trigger efficiency for minimum bias events
For Au+Au or Cu+Cu collision : ~
23/03/2007
Andry Rakotozafindrabe – LLR

35. Collision geometry and centrality (eg : Cu+Cu)
Participants
(charged particles)
QBBC
Spectators
(neutrons)
EZDC
For a given b, Glauber model (Woods-Saxon function) predicts:
Npart (No. participants)
Ncoll (No. binary collisions)
10 fm b fm
Npart
Ncoll
BBC charge N+S distribution for min.bias Cu+Cu √s = 200 GeV data
80-88%
70-80%
etc
Monte-Carlo Glauber model
Probability for a given Npart
Each participant contributes to
a Negative Binomial distribution of hits
Fit BBC charge distribution
23/03/2007
Andry Rakotozafindrabe – LLR

36. tsecondaries formation
Energy density
Longitudinally expanding plasma :
dET/dη measurement at mid-rapidity by PHENIX EMCal
Which τ0 ?
pR2 t0
~ 1 fm/c
tcross
~ 0.13 fm/c
tsecondaries formation
~ 0.35 fm/c
ttherm
~ fm/c
23/03/2007
Andry Rakotozafindrabe – LLR