1. Strongly Interacting Matter Under Extreme Conditions
Charmonia in
Heavy Ion Collisions
Roberta Arnaldi
INFN Torino (Italy)
Strongly Interacting Matter Under Extreme Conditions
Hirschegg, January 2010

2. Outline
Charmonia suppression in AA collisions is already a 25 years long story
SPS
RHIC
LHC √s
17 GeV/c
200 GeV/c
5.5 TeV/c
years
1986
1990
~2000
2010
Last year, new high precision data (HERA-B, NA60, PHENIX/STAR) have been presented
improvements in the understanding of the charmonium behavior, taking advantage of the different energy and kinematics exploited domains

3. Physics motivation: AA collisions
Study of charmonium production/suppression in pp, pA and AA collisions
AA collisions
Charmonia suppression has been proposed, more than 20 years ago, as a signature for QGP formation
Sequential suppression of the resonances is a thermometer of the temperature reached in the collisions
T/TC
J/(1S)
c(1P)
’(2S)

4. Physics motivation: pp, pA collisions
pp collisions
(not covered by this talk)
provide information on production models (CSM, NRQCD, CEM…)
provide a reference for nuclear collisions results
pA collisions
allow the understanding the J/ behaviour in the cold nuclear medium
 complicate issue, because of many competing mechanisms:
Final state:
cc dissociation in the medium,
final energy loss
Initial state:
shadowing,
parton energy loss,
intrinsic charm p μ
J/
provide a reference for the study of charmonia dissociation in a hot medium
 approach followed at SPS and similarly at RHIC (with dAu data)

5. Fixed target experiments

6. Fixed target experimental landscape
(Relatively) large amount of fixed-target data (SPS, FNAL, HERA)
AA collisions
NA38 S-U 200 GeV/nucleon, 0<y<1
(M.C. Abreu et al., PLB449(1999)128)
NA50 Pb-Pb 158 GeV/nucleon, 0<y<, pT<5 GeV
(B. Alessandro et al., EPJC39 (2005)335)
NA60 In-In 158 GeV/nucleon, 0<y<1, pT<5 GeV
(R. Arnaldi et al., PRL99(2007) , Nucl. Phys. A 830 (2009) 345)
pA collisions
HERAB p-Cu (Ti) 920 GeV,-0.34<xF<0.14,pT<5 GeV
(I. Abt et al., arXiv: )
E p-Be,Fe,W 800 GeV,-0.10<xF<0.93,pT<4 GeV
(M. Leitch et al., PRL84(2000) 3256)
NA p-Be,Al,Cu,Ag,W,Pb,400/450 GeV,-0.1<xF<0.1,pT<5 GeV
(B. Alessandro et al., EPJC48(2006) 329)
NA p-p p-Pt, 200 GeV, 0<xF<0.6, pT<5 GeV
(J. Badier et al., ZPC20 (1983) 101)
NA p-Be,Al,Cu,In,W,Pb,U 158/400 GeV,-0.1<xF<0.35,pT<3 GeV
(E. Scomparin et al., Nucl. Phys. A 830 (2009) 239)

7. Fixed target experimental results
Anomalous J/ suppression in AA is evaluated wrt to a reference obtained extrapolating, from pA to AA, the CNM effects affecting the J/
pA collisions
In the NA50 approach:
all initial/final CNM effects are described through an effective abs. cross section absJ/
obtained from pA at 400/450 GeV (NA50)
absJ/ = 4.2±0.5 mb, (J//DY)pp =57.5±0.8
(Glauber analysis)
extrapolated to AA at 158 GeV assuming
~e−ρLσabs
absJ/ (158 GeV) = absJ/ (400/450 GeV)
(J//DY)pp rescaled from 450/400 to 158 GeV
AA collisions
In-In
Pb-Pb
Observed suppression in AA exceeds nuclear absorption
Onset of the suppression at Npart  80
Good overlap between Pb and In
(R. Arnaldi et al., PRL99(2007) )

8. Cold nuclear matter effects
To understand the J/ dissociation in the hot matter created in AA collisions, cold nuclear matter effects have to be under control
These effects can be quantified, in pA collisions, in two ways:
I. Abt et al., arXiv:
E866 vs HERAB (similar √s)
 agreement in the common xF range
E866/HERAB vs NA50
  decreases when decreasing √s
Strong xF dependence of 
 Satisfactory theoretical description still unavailable!
(R. Vogt, Phys. Rev. C61(2000)035203,
K.G.Boreskov A.B.Kaidalov JETP Lett. D77(2003)599)
Because of the  dependence on xF and energy
 the reference for the AA suppression must be obtained under the same kinematic/energy domain as the AA data

9. New NA60 pA data
NA60 has collected pA data (using 7 different targets):
158 GeV: no data available up to now.
 First pA data at the same energy as AA collisions
400 GeV: already investigated by NA50 (cross check)
A-dependence of the relative cross sections is fitted using the Glauber model and abs is extracted
shadowing neglected, as usual (but not correct!) at fixed target
abs J/ (158 GeV) = 7.6 ± 0.7 ± 0.6 mb
abs J/ (400 GeV) = 4.3 ± 0.8 ± 0.6 mb
Very good agreement with the NA50 value
Using
(158 GeV) = ± ± 0.008
 (400 GeV) = ± ± 0.009
E. Scomparin et al., Nucl. Phys. A 830 (2009) 227

10. Comparison between experiments:  vs xF
NA60 pA results can be compared with  values from other experiments
In the region close to xF=0,
increase of  with √s
NA GeV
very good agreement with NA50
NA GeV:
 smaller , hints of a decrease towards high xF ?
Systematic error on  for the new NA60 points ~0.01

11. Comparison between experiments:  vs x1,2
 pattern vs x1 at lower energies resembles HERA-B+E866 but systematically lower
shadowing effects and nuclear absorption scale with x2
(V. Tram and F. Arleo, arXiv: )  clearly other effects are present

12. Kinematical dependence of nuclear effects
Interpretation of results not easy
 many competing effects affect J/ production/propagation in nuclei
anti-shadowing (with large uncertainties on gluon densities!)
final state absorption…
 need to disentangle the different contributions
Size of shadowing-related effects may be large and should be
taken into account when comparing results at different energies
158 GeV
free proton pdf
EKS98
158 GeV
free proton pdf
C. Lourenco et al., arXiv:
Le 2 curve non sono a 1 perche’ il ref e’ il Be senza shad
Conta la forma, non la norm.
SPS charmonia explores a range of x corresponding to the antishadowing region, where parton densities in the nuclei are enhanced with respect to those of free nucleons
without antishadowing: 7.6± 0.7± 0.6 mb
abs J/ (158 GeV)
with antishadowing (EKS) = 9.3± 0.7± 0.7 mb
Significantly higher than the “effective” value

13. Kinematic dependence of nuclear effects (2)
Apart from shadowing, other effects not very well known, as parton
energy loss, intrinsic charm may complicate the picture even more
First attempts of a systematic study recently appeared
(C. Lourenco, R. Vogt and H.Woehri, JHEP 0902:014,2009, INT Seattle workshop 2009, F. Arleo and Vi-Nham Tram Eur.Phys.J.C55: ,2008, arXiv: )
No coherent picture from the data
 no obvious scaling of  or abs with any kinematical variable
Clear tendency towards
stronger absorption at low √s

14. Reference for AA data
a precise reference for the J/ behavior in AA collisions can be determined
abs shows an energy/kinematical dependence
reference now obtained from 158 GeV pA data (same energy/kinematical range as the AA data, contrarily to what was done in the past)
AA collisions shadowing affects not only the target, but also the projectile
proj. and target antishadowing taken into account in the reference determination
In-In 158 GeV (NA60)
Pb-Pb 158 GeV (NA50)
Using the new reference:
Central Pb-Pb: still anomalously suppressed
In-In: almost no anomalous suppression?
In-In analysis based on another centrality estimator (number of tracks) ongoing, to check the observed pattern
B. Alessandro et al., EPJC39 (2005) 335
R. Arnaldi et al., Nucl. Phys. A (2009) 345
R.A., P. Cortese, E. Scomparin Phys. Rev. C 81,

15. Collider experiments

16. Collider experimental landscape
Data from RHIC, waiting for high energy LHC collisions…
Experiments
PHENIX J/e+e- |y|<0.35 & J/+- |y| [1.2,2.2]
STAR J/e+e- |y|<1
AA collisions
Au-Au 200 GeV/nucleon PHENIX, PRL (2007)
Nucl.Phys.A 830 (2009) 331
Cu-Cu 200 GeV/nucleon PHENIX, PRL (2008)
STAR, Phys. Rev. C (2009)
pp, dA collisions
pp 200 GeV/nucleon PHENIX, PRL 98, (2007)
STAR, Phys. Rev. C (2009)
dAu 200 GeV/nucleon PHENIX, Phys.Rev.C (2008)
Nucl.Phys.A 830 (2009) 227
All data have been collected with the same collision energy (√s = 200 GeV) and kinematics

17. pp experimental results
pp results should help to
understand the J/ production mechanism
provide a reference for AA collisions (RAA)
arXiv:
C.L. da Silva, Nucl. Phys. A 830 (2009) 227
No physical meaning. Some STAR data (high pt already with run 6)
RHIC J/ results are usually provided as in terms of nuclear modification factor
The pp reference, used up to now, is based on Run 5
 improvement expected from new Run 6 high statistics data

18. AA experimental results
AuAu
PRL 101, (2008)
Phys. Rev. Lett 98, (2007)
The Npart dependence of RAA for CuCu and AuAu is consistent
J/ suppression is stronger at forward rapidity wrt. to midrapidity

19. CNM effects from dAu
In a similar way as at SPS, CNM effects are obtained from dAu data
RHIC data exploit different x2 regions corresponding to
 shadowing (forward and midrapidity)
 anti-shadowing (backward rapidity)
Backward
Mid
Forward
RdAu is fitted with a theoretical calculation assuming
nuclear modified PDF distibutions
breakup
The result is the extrapolated to AA y
Phys. Rev. C 77, (2008)
Nuclear modifications to the PDF
Several approaches used
results from dAu Run 3 do not allow to draw conclusions on AA results, because of the large breakup error

20. CNM effects from dAu (2)
Furthermore CNM effects may depend on the assumed J/ production mechanisms (E. Ferreiro et al. arXiv: )
intrinisic (gg  J/)
extrinsic (gg  J/ + g) (emission of a hard gluon)
following emission of soft gluon(s) does not modify kinematics
To be checked with new data. Extrinsic for each y,pt x1 and x2 are not uniquely defined
J/ produced through different partonic processes involve gluons in different x2 region  different shadowing corrections

21. The Run8 dAu data
Now high statistics dAu data (Run8 ~ 30x Run3) are available
EKS98: 0,1,…4,…mb
a single value of break-up cannot reproduce the RCP ratios
RCP flat vs centrality at backward rapidity, but falls at forward y
A new approach has been proposed, to evaluate CNM effects
(T. Frawley ECT*,INT quarkonium,Joint Cathie-TECHQM workshop)
RCP vs. centrality is fitted for each y bin with
 a breakup for each y range
a shadowing parameterization

22. RAA/RAA (CNM) breakup shows a strong rapidity dependence
Result is then extrapolated to AA
midrapidity
backward y
forward y
Non c’e’ dipendenza perche’ shadowing e sigma breakup si compensano
the trend at high y is similar to the one observed by E866
the suppression beyond CNM effects is found to be similar at y=0 and at y=1.7
There is essentially no dependence of these results on the shadowing model used to parameterize the dAu RCP
(T. Frawley Joint Cathie-TECHQM workshop)

23. Comparison with SPS results vs NPart
Measured/Expected SPS results are compared with RHIC RAA results normalized to RAA(CNM)
Both Pb-Pb and Au-Au seem to depart from the reference curve at NPart~200
For central collisions more important suppression in Au-Au with respect to Pb-Pb
Au shadowing parametrization is used
Systematic errors on the CNM reference are shown for all points
still some model dependence also in this approach:
Cu results are fitted using breakup from dAu, since dCu data do not exist

24. Comparison with SPS results
Results are shown as a function of the multiplicity of charged particles (~energy density, assuming SPS~RHIC)
Comparison can also be done in terms of  * Bjorken energy density
energy density evaluation is based on several assumptions
Equivalent to energy density for tau=1fm/c
 dET/d from WA98 data for SPS data
 no dET/d for CuCu, so AuAu data at the same NPart are used
 complicate issue, in particular when comparing results from different experiments

25. Interpretation of the results
Several theoretical models have been proposed in the past, starting from the following observations
RAA at forward y is smaller than at midrapidity
RAA at RHIC and SPS are similar, in spite of the very different √s
Different approaches proposed:
1) Only J/ from ’ and c decays are suppressed at SPS and RHIC
 same suppression is expected at SPS and RHIC
 results do not seem to reflect the sequential suppression
Sequential melting: jpsi not suppressed: Reasonable if TdissJ/~ 2Tc
2) Also direct J/ are suppressed at RHIC but cc multiplicity high
SPS
RHIC
LHC
s (GeV)
17.2
200
5500
Ncc
≈ 0.2
≈10 ≈
 J/ regeneration ( Ncc2) contributes to the J/ yield
 The 2 effects may balance: suppression similar to SPS

26. Recombination
Models including J/ regeneration qualitatively describe the RAA data
(X. Zhao, R. Rapp arXiv: , Z.Qu et al. Nucl. Phys. A 830 (2009) 335)
Direct way for quantitative estimate
 accurate measurement of charm 
Indirect way
 some distributions should be affected by regeneration
J/ elliptic flow
 J/ should inherit the positive heavy quark flow
Electrons from open charm/beauty show positive v2
Narrow pt because only close cc pairs can combine and low pt charm quark dominate the spectrum
J/ y distribution
 should be narrower wrt pp
J/ pT distribution
 should be softer (<pT2>) wrt pp
Results are not precise enough to assess the amount of regeneration

27. High pT J/ in Cu-Cu PHENIX (minimum bias)
STAR (centrality 0-20% & 0-60%)
RCuCu =1.4±0.4±0.2 (pT>5GeV/c)
 RAA increases from low to high pT
RCuCu up to pT = 9 GeV/c
 suppression looks roughly constant up to high pT
Ads/CFT -> at high pt J/Psi dissociation T decreases  more suppression
NA50: Pb-Pb
Difference between high pT results, but strong conclusions limited by poor statistics
Both results in contradiction with AdS/CFT+Hydro
Increase at high pT already seen at SPS

28. Statistical hadronization
J/ production by statistical hadronization of charm quarks
(Andronic, BraunMunzinger, Redlich and Stachel, PLB 659 (2008) 149)
charm quarks produced in primary hard collisions
survive and thermalize in QGP
charmed hadrons formed at chemical freeze-out (statistical laws)
no J/ survival in QGP y
Raa higher at midrapidity because of the rapidity dependence of charm production sigma
A. Andronic et al. arXiv:
Good agreement between data and model
Recombination should be tested on LHC data!

29. LHC perspectives

30. Quarkonium physics at LHC
New scenarios will be accessible, thanks to the high beam energy
Factor 10 (100) increase in charmonia (bottomonia)  with respect to RHIC
 Bottomonium physics will be accessible
High charm quark multiplicity (NCC~100)
 J/ regeneration (not yet well defined at RHIC) might become dominant
Pb ions will be accelerated (√s=5.5 TeV)
p collisions will be also studied (√s=7 – 14 TeV)

31. Charmonium performances @ LHC
Charmonia measurements will be carried out by all the LHC experiments under different kinematical conditions
ALICE
ATLAS
CMS
LHCb
Acc
(M)
S/B pT
ALICE(+-)
ALICE(e+e-)
ATLAS(+-)
CMS(+-)
2.5<<4
-0.9<<0.9
-2.7<<2.7
-2.4<<2.4
70 MeV
30 MeV
0.13 (7)
>0 GeV/c
indirect id.
1.2 (5)
yes
yes?
>2 GeV/c
35 MeV
1.2
0.15
prompt/
displ.
Comparison of J/ measurement in central PbPb collisions
Simulations with dNch/d~

32. ALICE
ALICE is the LHC experiment dedicated to nucleus-nucleus collisions
Central Barrel:
-0.9<<0.9
e+e- decay channel
Forward Muon Arm
2.5<<4
+- decay channel
Quarkonium physics that will be addressed:
Suppression of in AA collisions
to study the created medium
Differential distributions
(y,pT,polarization)
 to constrain production models
 to provide a reference for AA
Quarkonium production will be measured in the central barrel and in the forward muon spectrometer in p-p and Pb-Pb collisions

33. Quarkonium in central Pb-Pb
Quarkonium in central Pb-Pb collisions (106 s running time, L=51026cm-2 s-1)
Central rapidity
Forward rapidity
e- identification in TPC+TRD
integrated J/ acceptance ~29%
 identified in a Muon Spectrometer
integrated J/ acceptance ~4.6%
J/  N.
103
M MeV/c2 30 80
S/B
1.2
1.1
S/√(S+B)
245 21
J/
(2S)  N.
M MeV/c2 70
100
S/B
0.2
0.01
1.7
S/√(S+B)
150 7 29
Level-1 trigger (pT cut > 3GeV) not applied for central PbPb
No psip per central rap
Simulations with dNch/dy~3000
Simulations with dNch/dy~8000
J/ and  significances not so different smaller statistics compensated by background reduction
Worst situation for the ’ statistics  , but much larger background

34. Quarkonium in Pb-Pb
With the expected statistics (~7 105 J/ in 1 month of data taking):
 J/ suppression can be studied as a function of centrality and pT (up to ~10GeV/c), allowing the discrimination between the different theoretical scenarios
 J/ polarization study will be performed as a function of pT
A fraction of the J/ produced at LHC comes from the B hadron decay
 useful to evaluate the beauty production cross section
need to be disentangled to study prompt J/ production
At midrapidity  prompt and secondary J/ can be discriminated thanks to the vertexing capabilities.
At forward y  J/ from B can be determined only indirectly
Higher charmonia states (’, c) can be measured
 cleaner signal for theory
 feasible in pp, much more complicate in Pb-Pb because of the lower significance

35. First ALICE dimuons!
First dimuons seen in ALICE in pp at √s=900GeV, even if out of the ~20 observed dimuons… not yet a J/!

36. Conclusions J/ suppression is a good signature for QGP studies
but for a correct evaluation of anomalous effects, cold nuclear matter effects have to be under control
J/ behaviour in cold nuclear matter is already a complicate issue: many competing initial/final state effects
Many steps forward thanks to new high precision data
Signal of anomalous suppression has been observed at SPS and RHIC
Important to understand J/ behaviour from lower to higher energy in a coherent scenario
New LHC data will soon be available!
They will help to discriminate among the different processes (suppression, regeneration…) affecting the J/
In the future, the “J/ picture” will be enriched by the results from CBM, exploring a baryon rich matter, and maybe from a NA60-like experiment filling the gap between FAIR and top SPS energy

37. Backup

38. NA60 pA data 158 GeV 400 GeV NA60 has collected pA data:
158 GeV: no data available up to now.
 First pA data at the same energy as AA collisions
400 GeV: already investigated by NA50 (cross check)
 3-day long data taking, largely motivated by the
need of a reference sample taken in the same conditions of In-In (NA60) and Pb-Pb (NA50) data
 useful to enlarge the  vs xF systematics
158 GeV
 bulk of the NA60 p-A data taking
 results released up to now
sub-sample with same exp. set-up used at 158 GeV
useful as a cross-check (same energy/kinematic domain
of the large statistics data sample collected by NA50)
400 GeV
0.28 < ycm < (158 GeV)
Kinematical window where acceptance is >0 for all targets
3.2 < ylab < 3.7
-0.17 < ycm < (400 GeV)
| cos CS | <0.5

39. New NA60 pA results
Not enough DY statistics to extract (as in NA50) B J//DY target by target DY
J/, ’ DD
Comb.bck.
p-Pb
NJ/  2  103
Estimate of nuclear effects through relative cross sections:
all targets simultaneously on the beam
beam luminosity factors Niinc cancel out (apart from a small beam attenuation factor)  no systematic errors
each target sees the vertex spectrometer under a (slightly) different angle
acceptance and reconstruction efficiencies do not completely cancel out
Efficiency map
(4th plane, sensor 0)
These quantities, and their time evolution, are computed for each target separately

40. Comparison between experiments: abs vs xF
absJ/ calculated from cross section ratios for HERA-B, E866,NA3
As already observed for , there is:
a strong xF dependence
a √s dependence…but NA3 shows values closer to the high energy experiments (E866/HERA-B)

41. Results with old and new reference
abs J/ (158 GeV) > abs J/ (400 GeV)
smaller anomalous suppression expected with respect to previous results
new reference
In-In 158 GeV (NA60)
Pb-Pb 158 GeV (NA50)
published results
B. Alessandro et al., EPJC39 (2005) 335
R. Arnaldi et al., PRL99 (2007)
Anomalous suppression in In-In is quite small ( 10%)
Anomalous suppression in Pb-Pb up to 30%
In-In analysis based on another centrality estimator (number of tracks) ongoing, to check the observed pattern

42. Antishadowing contribution
In AA collisions the initial state effects (shadowing) affect not only the target, but also the projectile
proj. and target antishadowing taken into account in the reference determination
Even in absence of anomalous suppression, the use of the standard reference (no shadowing) induces a 5-10% suppression signal
 sizeable effect
Using the new reference (shadowing in the projectile and target)
Central Pb-Pb: still anomalously suppressed
In-In: almost no anomalous suppression?
R.A., P. Cortese, E. Scomparin
Phys. Rev. C 81,

43. CNM effects from dAu
As discussed for SPS data, a good knowledge of the initial/final state effects in nuclear matter helps to understand the J/ behaviour in AA
CNM effects at RHIC energies can be inferred from dAu data, using different approaches
1st method y
Phys. Rev. C 77, (2008)
RdAu is fitted with a theoretical calculation assuming a shadowing parameterization and a breakup common to the whole y range.
The result is the extrapolated to AA
Since breakup is common, results in the two y ranges strongly depend on nPDF

44. CNM effects from dAu 2nd method
Npart
PRL 101, (2008)
2nd method
RdAu data are fitted with a theoretical model including a breakup for each y range and shadowing parameterization
Results are limited by the low Run 3 statistics
3rd method
The approach is based on a combination of RdAu data at different y, to predict CNM RAA for AuAu
J. Phys. G34, S955 (2007)
The method works only for AuAu, since RdAu is used directly
Results at different y are independent, but they again suffer the Run 3 low statistics

45. abs vs. y

46. High pT J/ @ SPS NA60: In-In @ 158 GeV
pT (GeV/c)
RCP
0-1.5%
pT (GeV/c)
RCP
33-47%
pT dependence of the J/ suppression already investigated at SPS energies:
 strong pT dependence of RCP
 only the low pT J/ψ are suppressed !
NA50: 158 GeV

47. First Upsilon results @ RHIC
STAR
PHENIX, STAR √s=200GeV
Cross section follows CEM expectations
PHENIX
RdAu = 0.98 ± 0.32 ± 0.28
PHENIX √s=200GeV
consistent with Nbin scaling
Low material dAu (talk Liu)
dAu and AuAu do not account for physical bck (DY, open beauty) below upsilon. They contribute up to 10-15% in pp
Upsilons suppressed:
very low  statistics
RAuAu [8.5,11.5] < 0.64 at 90% C.L.
in the future:
as expected from CNM + sequential melting
Upcoming 50 pb GeV p+p run (5.6 pb-1 in run6 p+p)
RHIC II: high luminosity → separation of 1S, 2S, 3S states

48. …and more results on… STAR pp @ √s=200GeV
Small bck contribution allows the study of high pT J/ - hadron azimuthal correlations
from the comparison with model calculations BJ/ fraction = 13% ±5%
STAR: arXiv:
PHENIX √s=200GeV
J/ azimuthal flow measurement limited by statistics
v2 = –10 ± 10 |y|<0.35 & –9.3 ± 9.2
does not allow to differentiate between different models
in the measure pT range
Because of small bck contribution it is possible to study J/psi – hadron correlation
PHENIX
First measurement of J/ψ photoproduction in ultraperipheral collisions
 cross section (7633(stat)11(syst) b) consistent with theoretical predictions
N(J/) =
9.9  4.1  1.0

49. Sequential melting
In a color screening suppression scenario, a sequential melting, starting from the most loosely bound charmonia state, is expected
are the SPS and RHIC J/ suppression in the hot medium similar enough to justify this assumption?
can the c and ’ feed down account for the observed J/ suppression?
CGC: gluon saturation at forward y
are other mechanisms (e.g. color glass condensate) needed to explain the different suppression at midrapidity vs forward rapidity?

50. Recombination
In a dense medium, J/ may be formed by a c and a c belonging to a different initial cc pair
regeneration is expected to be more important at midrapidity
A good accuracy in the open charm cross section measurement should help to quantify the importance of this process
Grandchamp, Rapp, Brown
PRL 92, (2004)
Thews
Eur.Phys.J C43, 97 (2005)
Open charm distribution peaked at midrapidity
RHIC patterns are qualitatively reproduced

51. Recombination
Models including J/ regeneration qualitatively describe the RAA data
(X. Zhao, R. Rapp arXiv: )
Regeneration should affect several distributions:
J/ elliptic flow  J/ should inherit the positive heavy quark flow
Electrons from open charm/beauty show positive v2
Narrow pt because only close cc pairs can combine and low pt charm quark dominate the spectrum
J/ pT distribution
 should be softer (<pT2>) wrt pp
J/ y distribution
 should be narrower wrt pp
Results are not precise enough to assess the amount of regeneration