1. Disentangling Charmonium Suppression
L. A. Linden Levy
for the PHENIX collaboration
Department of Physics
390 UCB
University of Colorado
Boulder, CO

2. Why Charmonium?
“If high energy heavy ion collisions lead to the formation of a hot quark-gluon plasma, then colour screening prevents cc binding in the deconfined interior of the interaction region.” Matsui & Satz, 1986
Debye screening (from EM plasmas) is a modification a particle’s potential due to the charge density of the surrounding medium.
One way to look at it is that the charmonium potential well is modified in the medium to become shallower.
T=Tc
T=0
In Medium
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

3. Predictions inspired by correlations in LQCD.
Rather than look at potential model that may not apply one can study spectral functions on the lattice.
Sets upper limits for charmonium melting temperatures
hep-ph/ v2
J/ψ (1S)
hep-ph/ v2
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

4. Measuring charmonium in PHENIX
Central Arms:
Hadrons, photons, electrons
J/ψ→ e+e-; ψ’ → e+e-; χc → e+e-γ
|η|<0.35
pe > 0.2 GeV/c
Δφ=π(2 arms x π/2)
Forward rapidity Arms:
Muons
J/ψ → μ+μ-
1.2<|η|<2.2
pμ > 1 GeV/c
Δφ = 2π
Global detectors
Beam-Beam Counter (BBC)
Zero Degree Calorimeter (ZDC)
Reaction Plane Detector (RxNP)
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

5. Pre-Requisites for understanding suppression.
Production mechanisms.
Feed down from higher states.
Cold nuclear matter effects.
Regeneration (coalescence) of uncorrelated pairs.
Account for all the J/Psi …. Make US economy joke here….
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

6. Production Mechanisms

7. Measuring the p+p baseline.
Measured p+p over a wide range in rapidity and transverse momentum with excellent precision.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

8. J/ψ polarization at PHENIX
λ = +1 (transverse)
= -1 (longitudinal)
Within uncertainty no polarization seen at PHENIX
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

9. CDF J/ψ puzzle
CSM gave a prediction that was an order of magnitude low.
COM does better but has free parameters in the overlap matrix (probability of emitting the soft gluon) and it predicts large longitudinal polarization.
New paper from Lansberg et al.
Modification to the CSM with a 4-point interaction can reproduce the data.
CSM
CSM+COM
Phys Rev D
PRL 79, 4
hep-ph/ v2
CDF CSM too low by a factor of 10 COM free parameters and large pol. Let people know what sigl and sigt are interesting that lansberg et al. can get a better agreement. Discuss what the model they have is, move Kirin until later top plot is CSM, I need a COM plot to overlay by animation
CSM +4p
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

10. Testing models with PHENIX
hep-ph/ v2
Good agreement with RHIC data too.
Extrinsic (i.e. CSM + 4-point)
Physically takes into account the interaction between pair before color neutralization
Can lead to different rapidity to parton momentum mapping as compared to CEM . (more on this when we talk about CNM effects)
CDF CSM too low by a factor of 10 COM free parameters and large pol. Let people know what sigl and sigt are interesting that lansberg et al. can get a better agreement. Discuss what the model they have is, move Kirin until later
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

11. Feed down from higher states.

12. The idea behind feed down
Measure fraction of the observed J/ψ from the decay of higher states. (p+p)
If the these higher states (i.e. χc ) melt due to color screening in a HI collision before the J/ψ then this contribution to the total yield will be missing.
It is crucial to measure two things:
Feed down fraction R(X) = N (XJ/ψ) / N (J/ψ) (p+p)
Higher energy states in HI collisions? (do they melt?)
With forward calorimetry PHENIX could measure χc
The silicon upgrade will enable PHENIX to separate J/ψ and ψ’ in the muon arms.
No acceptance for chi_c in the central arms, bad mass resolution in the muon arms.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

13. Feed down from ψ’ (p+p) R(ψ’) =8.6±2.5% PHENIX (QM08)
R(ψ’) =8.0±2.0% from the lattice (Phys.Rev.D64:094015)
R(ψ’) =8.1±0.3% from average of world data (hep-ph/ v1)
’ →e+e-
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

14. Feed down from χc (p+p) c →J/ +  R(c) <42% (90%C.L.) PHENIX
R (c) = 30% ± 8.0 Lattice (Phys.Rev.D64:094015)
R (c) = 25% ± 5.0 World average (hep-ph/ v1) (final Hera-b : 18% ± 2.8% hep-ex/ v1)
If the c melts in Au +Au 200GeV collisions 20-30% of the J/ disappear !
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

15. Cold nuclear matter effects

16. Nuclear modification factor.
Suppression due to normal density nuclear matter in d+Au 200GeV (run-3)
Reference set is consistently analyzed p+p 200GeV data (run-5)
Forward
Mid
Backward d Au
Calculate RdAu from nPDF parameterization and fit free parameter for breakup cross section.
Phys Rev C 77, Au d
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

17. Mistake in extracting σbreakup vs. rapidity
Phys Rev C 77,
The data points, statistical and systematic uncertainties in the figure are correct.
The one standard deviation uncertainty band for the breakup cross section contains a mistake.
The band does not account for all the systematic uncertainties, as intended in the paper.
Correctly including the systematic uncertainties will make the band larger.
We expect to release corrected values soon. Au d
Phys Rev C 77,
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

18. Making Predictions for Au+Au.
Mid-rapidity
Forward rapidity
Uncertainty and for CNM effects will get wider.
These are model dependent results, one has assumed that the nuclear modified PDFs are correct, a specific production mechanism and Glauber geometry.
No more slides with this error in this presentation.
I know that I am jumping ahead but lets get this out of the way
* The uncertainty bands contain the mistake described on previous slide
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

19. RdAu versus centrality
Nuclear suppression also measured as a function of centrality.
Hint of increase as we proceed to more central collisions, especially at forward rapidity.
But, a flat line would also fit most of the data well.
high x d Au b
low x
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

20. Let’s go back to the data.
How can they get such different curves with the same breakup cross section and the same nPDF parameterization?
The production mechanism changes the relationship between rapidity and parton momentum fraction.
hep-ph/ v1
So let’s go back to looking at the data
Talk by RGdC
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

21. Careful with this energy dependence talk.
First the error bar on the PHENIX result is going to grow so that there is more uncertainty in σbreakup within the production model assumed.
Secondly if this new production mechanism is correct then a breakup cross section closer to that from the SPS is found.
Theoretical message unclear σ(s) or σ=0. M. A. Braun et al., Nucl. Phys. B 509 (1998) 357
A. Capella and E. G. Ferreiro (hep-ph/ )
Very preliminary
PHENIX?
Talk by RGdC
200
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

22. J/ψ in heavy ion collisions

23. Nuclear suppression factor in HI.
Au+Au Phys Rev Lett 98:232301
Cu+Cu: Phys Rev Lett 101:122301
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

24. Features of the RHIC QGP.
Comparison to SPS
RAA (RHIC) ≈ RAA (SPS)
Not what’s expected from
εSPS (√s=20) < εRHIC (√ s=200)
Different rapidity (0 < ysps < 1)?
Different shadowing and σbreakup?
PHENIX Rapidity trend
RAA (|y|<.35) > RAA (1.2<|y|<2.2)
Challenges “local density” based suppression models.
But boon for coalescence models where yield is based on proximity in phase space.
Scomparin (proc. QM06) : nucl-ex/
Global error = 7%
Global error = 12%
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

25. Data-Driven CNM Projection
However, if we do not want to assume either of the previous models, then we may try a different approach.
In this case we assume that the modification factor depends only on the radial position in the nucleus. We can then use the measured RdAu vs. impact parameter to constrain this R.
R is the modification on J/ψ due to one Au nucleus, so we take R (+y)* R (-y) for Au+Au collisions.
R(r1,r2)
For more details see:
RGdC hep-ph/
PHENIX Phys Rev C 77 r2 r1
Talk by RGdC
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

26. Data driven method projection.
±12% Global Scale Uncertainty
±7% Global Scale Uncertainty
Mid-rapidity
Forward rapidity
This is a 1 sigm aerror band so we really need more data and the CNm could really account for the whole effect for instance there is this model of CGC by Kiril…
Some new models claim to account for all suppression with initial state effects (saturation, CGC) (Tuchin et al. hep-ph/ v1)
Talk by Taku Gunji and RGdC
*The data driven method projection uncertainty band is correct for this projection.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

27. Preview of RAuAu from run-7
Factor 4 more data than run-4.
The error bar represents the point to point uncorrelated error part of which comes from line shape.
We are working hard to reduce these systematics in the final result.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

28. Azimuthal Moments

29. More questions about charm in the QGP
Do the charm quarks thermalize? One signature is collective flow.
Can quantify charm regeneration by measuring open and closed charm elliptic flow
Coalescence imprints constituent flow onto resulting meson.
Careful… moment does not guarantee collective behavior i.e. energy loss
In run-7 PHENIX installed a reaction plane detector improve the resolution.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

30. v2 Result from PHENIX
Limited statistics do not allow one to differentiate between different models in the measure pT range.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

31. Future Measurements from PHENIX
(what we are working on now)

32. Run-6 & run-8 p+p 200GeV data. Run-8 d+Au 200GeV data.
Factor of three more data in run-6 compared to the previous run-5 p+p baseline.
Possibility to combine the run-6 and run-8 p+p to gain in a consistent manner to gain another factor (~four).
Precision of the data useful for theoretical predictions for normal production mechanisms
Run-8 d+Au 200GeV data.
Factor of thirty more data in run-8 compared to the previous run-3 d+Au .
Constrain the CNM effects present in HI collisions to make un-ambiguous statements about anomalous suppression.
The statistics are there! Main Focus is on reducing systematics.
250
Run-3
6000
Run-8
J/ψ → 2μ
50% data
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

33. Conclusions & Outlook
It is not clear that we see suppression beyond what can be explained by CNM at RHIC.
Model based prediction for CNM effects in HI collisions requires three components:
Production mechanism
Shadowing model+ Geometry
Break-up cross section
Data driven prediction method encompasses these features in a phenomenological parameterization.
New CNM measurements from run-8/run-6 will be available from PHENIX soon with more stat. & less systematic uncertainty.
PHENIX may have the opportunity to measure the c using forward calorimetry which would add vital information to this picture. The higher states are a key piece of this puzzle.
Mention data driven method in words.
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

34. Backup

35. New nPDF set to confront: EPS08
Inclusion of RHIC data (PHENIX, STAR, BRAHMS).
Large weight factor (40) given to the very forward negative hadron production data from BRAHMS.
Resulting in much larger shadowing in the gluon nPDF. (R. Vogt RHIC Users Mtg.)‏
No constant (with rapidity) break up cross section allows for the mid and forward PHENIX data within 1 sigma.
EPS08
EKS
nDSG Au d
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

36. CNM could cover the effect.
There is at least one model on the market that explains the data with only CNM effects.
The basic idea is that there is another contribution to the cross section coming from 3 gluon interactions.
These interactions are on par with the normal gluon fusion due to a factor of A1/3 coming from attaching one of the gluon lines to the nucleon (hep-ph/ v1)
Add more details….
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019

37. New state of matter at RHIC.
Definitely created something different:
RAA suppression of hadrons →but not photons
IAA jet suppression → Energy loss
Very dense medium
Collective behavior → flow
Are we seeing de-confined partons?
→ LQCD seems to predict ↑d.o.f. above TC ~170MeV
L. A. Linden Levy - SQM 2008 Beijing
4/22/2019