# Presentation: 704230

## J/ as a signal of deconfinement

- David Silvermyr, ORNL
- Critical Point and Onset of Deconfinement
- Firenze, July 4th 2006

*Focus on J/****  production results for p+p, d+Au, Au+Au and Cu+Cu** **at RHIC (next talk: results with* *fixed target).** *

**Notes:**
I’d first like to thank the organizers for the invitation. It’s a pleasure to be here.

I will discuss J/psi as a signal of deconfinement, and mainly discuss results from RHIC to date, and then you will here more in the next talk about results from the SPS etc.

## Heavy Quarkonia - Intro

- Lattice QCD results show that the confining potential between heavy quarks is screened at high temperature.

- This screening should suppress bound states such as J/.
- However, recent lattice results indicate that the J/ spectral functions only show modest modification near the critical temperature, and thus may not be suppressed until higher T.

**Notes:**
So, let’s start with a brief introuduction. As you know, there is a predicted screening between heavy quarks at high temperatures which should lead to suppression of states like the J/psi. However, recent results indicate that the J/psi may well survive and only be suppressed at temperatures well above the critical temperature T_C. So, this signal may not be as straightforward as once believed.

## Original Signature: Matsui & Satz (’86 & ’06)

*SPIRES : 934 citations so far (June ’06)*

**Notes:**
The original proposal for the J/psi signature of suppression a quark-gluon plasma came in the paper of Matsui and Satz 20 years ago. I don’t think I have ever seen a J/psi talk or paper in our field that didn’t mention this paper so I’m following a well-established tradition here :=)
This is one of the most quoted and famous papers in our field with almost a 1000 citatations, and since prof. Satz is here today let me add my congratulations also in addition to the celebrations held earlier this year at BNL, where this picture was taken.

## An Unambiguous Signature?

- Matsui and Satz carefully outlined the conditions that needed to be met for an observed suppression to be an unambiguous signature of QGP formation.
- Focus on one of these assumptions - may well be violated. .

**Notes:**
Even though it is a famous paper, not everyone may have read it, so..
They carefully...
We now know that there are competitive non-plasma effects that can cause normal J/psi suppression.
[First – we have seen that there are significant non-plasma suppression mechanisms, such as absorption by the colliding nuclei, absorption by co-moving materials and some combination of energy loss and shadowing.
Second – at least at collider energies, there are a significant number of c and c-bar pairs created in a central AuAu collision (roughly 10) thus inspiring much current theoretical activity to understand the creation of J/psi’s from a c and c-bar pair that were not primordial partners.]

## Competing J/ Production Effects

- Normal nuclear absorption:
- 	J/ breakup by nucleons in the final state resulting in charm hadrons
- Shadowing:
- 	Accounts for parton distribution modifications relative to free protons
- 	Affects parton distribution function before collision occurs
- Color Screening:
- 	In deconfined medium resonance interactions needed to convert cc pairs to J/’s are prohibited
- Comover Interactions:
- 	 J/ interactions with secondary hadrons results in dissociation
- 	Suppression mechanism that does not require deconfined medium
- Parton Induced Dissociation:
- 	Breakup of J/ due to in medium parton interactions
- J/ Recombination:
- 	Regeneration of J/’s from off-diagonal c and c pairs
- Feed-down effects, and more..

*A complex story: the devil is in the details..*

**Notes:**
Now, how about these competing effects regarding the production of  J/psi? Here I list some of them. First we have our normal nuclear effects like absorption and shadowing, then the effect of color screening in a deconfined medium. Then we have some other in-medium effect that can either cause the amount of J/psi to increase or decrease, such as co-movers and recombination. Furthermore, some J/psi come from feed-down of B and chi_c which further complicates the story. 
The purpose of this slide was just to say that this J/psi signal is a rather complicated story.. 

##     Pb+Pb collisions show suppression in excess of "normal" nuclear suppression
    (Recent news: NA60 observed very similar trend in In+In collisions.)

-     Pb+Pb collisions show suppression in excess of "normal" nuclear suppression
-     (Recent news: NA60 observed very similar trend in In+In collisions.)

- Suppression

- Expectation

- Observation at CERN SPS (NA50/60)** **

**Notes:**
Before we get to the RHIC results, I’d like to remind you of the results from NA50 and NA60 at the CERN SPS. Let’s focus on the plot on the right. They observed a significant suppression relative to their expectation at the more central Pb+Pb collisions. This trend has also recently been confirmed by NA60, as we’ll hear more about in the next talk.

Obviously it’s very important to have a very good handle of what the expectation should be for these comparisons.
The RHIC capability to collide many different species at the same energy is thus very important for a well-controlled measurement.

## CDF pp (s = 1.8 TeV) results

- Color singlet model underpredicts high-pT yield.
- Color octet model overpredicts transverse polarization at high pT.

**Notes:**
Note though that there are questions already about the J/psi production mechanism in pp collisions. 
[This is because while the initial production of c and c-bar is a hard process, the formation of the resonance with the correct quantum numbers is not. ]
The CDF data shown here are the pt-spectra for prompt psi and psi-primes. The curves are for the Color Singlet Model, which under-predicts the production by a large factor.
However, the Color Octet Model, which does a reasonable job at predicting the cross-section predicts significant transverse polarization of high-pt J/psi’s, which is not observed as shown here in a plot of the polarization parameter alpha vs pt for the two different states.

## J/ @ RHIC: Physics Plan 

- pp collisions
- Reference, Initial production mechanism
-      RHIC: can have same √sNN energy as pA and AA..
- pA  (or dA) collisions
- Shadowing
- Initial state energy loss
- Cold medium absorption
- AA + Light ion collisions
- Modify path length through medium
- Most efficient way to dial in Ncoll,Npart
- Energy scans
- Modify energy density
- More difficult (both luminosity & cross-sections fall quickly w/ energy)

*Many competing effects:*
*- Reference data essential!*

**Notes:**
This leads us to the overall J/psi plan at RHIC. By looking at pp collisions we get a reference, and can learn things about the initial production. With pA or dA we can quantify the normal or cold nuclear matter effects such as shadowing and absorption.
And then with heavy-ion collisions we can see how things evolve with centrality etc. 
Again, having a good reference is key.

## Charmonium and Beyond in STAR

- STAR Preliminary

**Dielectron Invariant Mass (GeV/c****2****)**

| Signal | RHIC Exp.
(Au+Au) | RHIC I
(>2008) | RHIC II | LHC
ALICE+ |
| --- | --- | --- | --- | --- |
| J/ →e+e
J/ → | PH ENIX | 3,300
29,000 | 45,000
395,000 | 9,500
740,000 |
| → e+e- 
 →  | STAR
PHENIX | 830
80 | 11,200
1,040 | 2,600
8,400  |

**J/******** Run4 AuAu**

**Dielectron Invariant Mass (GeV/c****2****)**

- STAR Preliminary

- J. Gonzalez, SQM06

- STAR AuAu
- preliminary

*Nice start with clear mass-peaks for AuAu and pp! *
*[part of total dataset analyzed] **	**	**Rest of talk:  focus on PHENIX**.*

**Notes:**
Now, I will spend the rest of the talk presenting results from PHENIX but before I get to that let me first show some plots here from STAR. This is from Johan Gonzalez recent presentation at Strange Quark Matter. On the top left you see mass-plots for different centrality slices in AuAu where clear peaks are seen even from what I understand is just from a subset of the total data. On the right you can see a mass-peak in pp and some conservative preliminary cross-section measurements below. So, I think it’s great that STAR is joining the game and you can see their expected yields for e.g. upsilons will be quite impressive. 

## RHIC Scaling Law : J/in PHENIX

| Year | Ions | sNN | Luminosity | Detectors | J/ |
| --- | --- | --- | --- | --- | --- |
| 2000
[Run-1] | Au+Au | 130 GeV | 1 b-1 | Central (electrons) | ~0 |
| 2001 | Au+Au | 200 GeV | 24 b-1 | Central | 13 + ~0  |
| 2002
[Run-2] | p+p | 200 GeV | 0.15 pb-1 | + 1 muon arm | 46 + 66  |
| 2002 | d+Au | 200 GeV | 2.74 nb-1 | Central | 300+800+600 |
| 2003
[Run-3] | p+p | 200 GeV | 0.35 pb-1 | + 2 muon arms | 100+300+120 |
| 2004
[Run-4] | Au+Au | 200 GeV
62 GeV | ~240 ub-1
~9 ub-1  | Central
+ 2 muon arms
 | ~500+2000+2000
 |
| 2005
[Run-5] | Cu+Cu
p+p | 200 GeV
200 GeV | ~3 nb-1
~3 pb-1 | Central
+ 2 muon arms | ~1000+5000+5000
~1000+5000+5000 |

- RHIC Scaling Law : J/in PHENIX

- Order of magnitude improvements for approx. every two RHIC runs – quite remarkable (another factor 3 for pp from Run5 to Run6) !
*	**Hope to see continued progress and success like this!*

**Notes:**
Let’s then go the PHENIX data.
This chart shows the runs to-date at RHIC, with the approx. number of J/psi’s in the right most column.
So far we have seen an exponential growth with statistics going up by an order of magnitude or so every run or two.
I think is quite impressive and let’s hope for continued progress and success like we have seen so far.

## Start: p+p Reference

- Phys. Rev. Lett. **96**, 012304 (2006).

- Consistent with trend of world’s data
- ~Consistent with at least one COM (Color Octet Model) calculation
- [Factor x10,
- and x30 more
- statistics from
- Runs5 and 6]

**Notes:**
So, with that, let’s go to the data.. This is first our overall cross section measurement in pp. You can compare our obtained values with the trend vs available energy from lower energy measurements and some color octet model calculations with differents PDFs.
I should note that this is from our lower statistics Run2&3 data sets and that we should be able to do a much better job with the Run5&6 data sets. 

##  d+Au: Disentangle Cold Nuclear Effects

- Cronin effect

- Gluon (anti-)shadowing

- Nuclear absorption.

- Initial state energy loss.

- gluons in Pb / gluons in p

- X

- Eskola, et al.,  Nucl. Phys. A696 (2001) 729-746.

- South (y < -1.2) : via +-
- large X2 (in gold)   ~ 0.090
- Central (y ~ 0) : via e+e-
- intermediate X2      ~ 0.020
- North (y > 1.2) : via +-
- small X2 (in gold)    ~ 0.003

**Notes:**
Next on our list is then d+Au vs p+p. What I want to show here is that covering different
regions in rapidity with our dilepton measurements, we do cover different regions in momentum fractions X of the gold partons, which means exploring different regions of shadowing and anti-shadowing.

## J/ rapidity distribution in p+p and d+Au Collisions

- Total cross section in p+p           (nucl-ex/0507032):
- 2.61+/-0.20(fit)+/-0.26(abs) μb

- J/ rapidity distribution in p+p and d+Au Collisions

**Notes:**
So, let’s move right into looking at the data. Here you see the measured rapidity distributions for pp and dAu. The estimated pp cross-section from the Run3 measurement, which you saw on an earlier slide, is about 2.6 micro-barns.
For dAu, you see that we saw more J/psi’s in the directions in the region the Au nucleus was heading. This corresponds to negative rapidity and a large momentum fraction x of the Au partons. 
Different rapidities correspond to different x-values for Au partons

## Rapidity and Ncoll Dependence of RdAu: Gluon Shadowing and Nuclear Absorption

- Data favor weak shadowing and weak nuclear absorption effect:
- Calc. with 1-3 mb most successful at describing the data.
- [Shape reminiscent to what’s seen for dNch/d(e.g. PHOBOS)]
- More suppression for more central events(?)

**Rapidity**

**Notes:**
We can turn these measurements into R_dA values and see how these evolve as a function of rapidity and centrality. The absorption appears to be fairly weak; a cross-section of the order 1-3 millibarn. The RdAu shape is also similar to what’s been seen for dNch/deta in PHOBOS. 
As for centrality effects; perhaps there is more of an effect for more central dA events although the centrality dependence is not quite conclusive with the current dataset from 2003.

## RUN5 pp News

- Beauty measurements will be quite interesting.

- Different Quarkonia states test the degree of color screening and measure the temperature.
- Significant yields (>hundreds) at RHIC-II ?

- PHENIX accumulated ~3pb-1 p+p collision during 2005 run.  Will give order of magnitude stat. improvement for reference for d+Au and Au+Au.

**Notes:**
These earlier measurements from Run3 were rather limited in statistics. In the previous un at RHIC we had a lot more statistics for the p+p reference. Even enough to give something that looks like an upsilon peak, which was very nice to see.
It is not in obvious disagreement with the sqrt(s) trend seen by other experiments, and future stat. improvements should help a lot. For truly significant large stat. yields we probably have to wait for RHIC-II.
I should note here that for this cross-section estimate we did assume that other contributions such as Drell-Yan was negligible, and assumed that the unlike-sign excess here at large masses was all due to upsilons, which is probably not quite true..
As you know, comparing the suppression of different quarkonia states can be quite important.

## Heavy Ions: J/ signal in Au+Au

- J/e+e-

- J/-

- PHENIX

**Notes:**
Now, let’s move on to the heavy-ion case.. Here I show some signal mass plots for different Au+Au centrality bins to give a feel for the approximate statistical accuracy for the signal. 
The recent Cu+Cu run resulted in larger statistics.

- RAA vs Ncoll (QM’05; nucl-ex/0510051)

**About a factor 3 suppression for most central Au+Au points**

- Band around 1.0 refers to the uncertainty of the p+p reference.
- [and sometimes has a global sys. error added for the dataset in question..]

**Notes:**
Here I show all the different datasets collected together, compared to pp.
dAu, AuAu, CuCu; for muons and electrons. The band around 1 indicates the error in the p+p reference and sometimes contains a global systematic also. As has been pointed out, this should be standardized.. 
We see about a factor of 3 suppression relative to pp for the most central collisions.

Good agreement between muon datasets where they overlap
Central arm points somewhat higher than muons but the rapidity window differs

## Results in A+A : vs cold nuclear matter effects

- |y|~1.7

- |y|~0

**suppression**
**factor ~ 2**

**suppression**
**factor ~ 2**

**3 mb**

**1 mb**

**3 mb**

**1 mb**

**Observe a suppression of ~3 from pp and ( ~ factor 2) beyond cold nuclear **
**effets.  Note common error boxes now (post QM05) around individual points.**
**.. Working on final results with reduced systematic errors ..**

**suppression**
**factor ~ 3**

**suppression**
**factor ~ 3**

**AA**

**AA**

**Notes:**
Here I have splitted up the data in the muon and central arm rapidities. We observe ..

## Au+Au and Cu+Cu results

- SPS normalized to NA51 p+p value (NA60 preliminary points from Arnaldi, QM05).

**On the experimental point of view :**
**Suppression at RHIC similar to suppression at SPS**
**Although √s@RHIC=200 GeV and √s@SPS<20 GeV**

**Need more precise measurement of cold nuclear effect at RHIC       **
****** ****need more dAu as well as AuAu data**

**Notes:**
If we look again at the data and compare it with the data from the SPS, which has smaller errors, we can see that the suppression pattern is rather similar between RHIC and SPS. We can then compare with the two cases of cold nuclear effects from RHIC 1 & 3 mb, and here we have first the 1mb case where the cold nuclear effects are different. Then with the 3mb they are quite similar. So, to clarify the situation further we need both more dAu as well as AuAu data.

## J/ : Suppression Models

**Some suppression models which reproduce NA50 data... **

**... ****Overestimate the suppression at PHENIX**

**(Hadronic?) co-mover scattering**

**Direct suppression in a hot medium :**

**Cu+Cu**

**Au+Au**

**AA**

**Notes:**
OK, let’s go back to the AuAu and CuCu J/psi data again. 
We can then start on some comparisons with models. Here are a few cases of models that can reproduce the NA50 data, and they tend to overestimate the suppression at RHIC.

## J/ Suppression in Heavy-ion Collisions May be Masked By Recombination Effects

- In central Au+Au collision there are many (>10) c/c-bar pairs produced in a single event.
- Calculations indicate that a significant number of J/’s could be produced by coalescing c and c-bar quarks that are the products of different hard scattering events.
**	**
- This would have the effect of masking suppression due to the presence of a QGP.

**Notes:**
One additional thing to consider for the heavy collisions at RHIC is that we have a significant amount of charm produced here, so recombination effects can start to be important and mask the suppression. 

[Ref: Phys. Rev. C73, 014904 (2006).]

## Comparison with a prediction w. regeneration

**[After update from Rapp et al to ****use up-to-date charm and J/******** p+p cross-sections****:]****   **
**agreement with data points  slightly better than that of absorption calculation (with 3 mb sigma).**

**Notes:**
Ralf Rapp et al provided an update of his calculation with the new numbers. The curve moved up a little for the more central collisions and the end agreement with the data is at about the same level as the absorption curves (with the probably a little too high sigma).  

## 

An alternative picture...

- An alternative picture...

**Notes:**
Before we try to conclude anything from what I have shown so far let us consider an alternative picture also.

## J/ Feeddown Effect

- J/ yield is populated from both direct production and feeddown from the higher resonance states
- Relative yield from each source experimentally found:
- 60% direct production
- 30% c feeddown
- 10% ’ feeddown
- Medium conditions determine whether each state exists in the bound form

**Notes:**
As I mentioned before, only some fraction of J/psi are from a direct production and a rather significant fraction could come from higher states. The fraction of feed-down from chi_c has been measured at other energies. Shown here from HERA is a result  that says this fraction is about 30%.

## Quarkonia production as a QGP thermometer

- Even if jet suppression, flow results, etc. have already established that the medium created at RHIC is an sQGP, we would still like to establish its properties.
- The quarkonium suppression pattern may be able to serve as a QGP thermometer.
- In cartoon form...
- It is argued that the common pattern seen at SPS and RHIC is due to complete suppression of ’ and c, which feeds down to create ~40% of the J/’s, and that the primordial J/’s aren’t suppressed at all by screening.

- H. Satz, J. Phys. **G32**, R25 (2006)

**Notes:**
I showed you before how one expects the different states to be suppressed as a function of temperature and here is a perhaps more up-to-date illustration of this idea, and I refer you this publication also for a more in depth discussion. A suggestion is that the common pattern at SPS and RHIC..

## CuCu: More Bins...

-  Rather smooth onset/scaling with centrality.. no distinct onset or plateau for c suppression, with our preliminary data & errors

**Notes:**
However, we do note that in our larger statistics data set from CuCu which should show the step-wise behavior we see more of a smooth/slow onset of the suppression. 

## Test of Npart scaling

- Can the results be explained by some other scenario? Geometry and
- surface effects or scaling a la soft processes?
- [argued for NA50 data by e.g. Gazdzicki, Braun-Munzinger et al.]

*Alternative looks at data may help to break gridlock..*

**Notes:**
Instead of doing the scaling with number of collisions, we can also do it with the number of participants, and then you see it plotted as a function of Npart. The trend is not flat at the pp value, but at least for muons, the data looks like a rather smooth curve. This sort of Npart scaling was also suggested for the NA50 data by Marek Gazdzicki and others.

## More variables : Rapidity

- Rapidity distribution of recombined J/ is supposed to be peaked at y=0 (e.g. R.L. Thews & al., nucl-th/0505055)
- True IF charm distribution ~ J/ in p+p !
- But Au+Au charm rapidity distributions might be rather flat!

**pQCD, adjust <k****T****2****>**

**p+p data**

**diagonal**

**off-diagonal**
**(with recomb.)**

**Notes:**
Looking at the data in different ways might be helpful.
A common feature for models with recombination is that they predict a narrowing of the rapidity distribution. However, this is based on the assumption that the charm rapidity distribution is also peaked, the charm rapidity distribution might be pretty flat.
The J/psi data does not show any dramatic changes vs centrality; pretty much the same shape as in pp.

## Invariant yield vs pt

- Invariant yield vs pt

- Cu+Cu (|y|[1.2,2.2])

- Au+Au (|y|[1.2,2.2])

**Notes:**
Anoter variable one can study is the invariant J/psi yield vs pT for different centralities. We can do simple fits to these spectra and extract the mean-pT squared. These are summarized on the next slide. 

## Mean transverse momentum vs Ncoll

**    ****Experimentally :**** data falls between the two hypotheses.**
**Need to consider all datasets and**
**error bars before drawing conclusions.**

**No recombination**

**With recombination**

- Open markers : |y|<0.35
- Solid markers : |y|~1.7

**Recombination (Thews et al., nucl-th/0505055)**** predicts a narrower p****T**** distribution, leading to a lower <p****T****2>**

**p+p****       ****d+Au**

**No recombination**

**With recombination**

**Au+Au**

- Open markers : |y|<0.35
- Solid markers : |y|~1.7

**Cu+Cu**

**p+p****   ****d+Au**

- Mean transverse momentum vs Ncoll

- Cronin / Broadening:

**Notes:**
Here we have split up the data so as to not overwhelm you, in first a CuCu plot and then a AuAu plot. Some data sets suggest a rise with more central collisions while the ones with smaller errors tend to be more flat.. 

## J/ Status

- RHIC data exhibits a **factor 3 suppression** for most central events in Au+Au collisions. Suppression vs Npart rather similar to what was seen at SPS.

- Comparison with models (here only used a subset..) suggests that
- 1) Models with only cold nuclear matter effects tend to under-predict the suppression
- 2) Models with color screening or comovers and without recombination have
-    too much suppression
- 3) Models with recombination are in rather reasonable agreement with the data
- Not clear if recombination is the explanation though. Feed-downs suppressed?

-  Pro(?): <pT2> is also consistent with flat behaviour, but large error bars.

- Mixed evidence for recombination from other variables:
-  Con(?): The rapidity dependence of the J/ yield shows no dramatic change in shape with increasing Npart.

**Notes:**
- Just go through the points - 

## J/ Action Items

- Need more work on data (in progress); reduce size of errors and go to final results. Using the statistically superior Run5 p+p dataset for reference should be helpful. It would be nice to confront theory with more precise results! :=)

- Flow? - J/ v2 studies started; no results yet. Statistically very challenging analysis with existing RHIC datasets. Comparison between charm and charmonium should be instructive.

- Question: Do we see (suppression + recombination) or just not so much suppression to start with..?
- [‘soft’ scaling and similarity with NA50 suppression pattern - somewhat surprising and hard to overlook. Just coincidences?]

**Notes:**
- Just go through the points for this and the following slides - 

## More data needed!

- In any case (and as usual..), more data is needed..
- Need to study
- Different quarkonia states (different melting points, different feeddown contributions).
- Different collision energies
- Modify charm quark density to change recombination fraction.
- Modify temperature.
- Better data vs. centrality, pT, y.
- Polarization, J/-hadron correlations, flow (for production mechanism).
- This physics is really just getting started at RHIC..

## Future Measurements: ’

- With more luminosity we should be able to measure ’ in AuAu too!

## Future Measurements: c

- Future Measurements: c

- PHENIX
- Run 5 200GeV p+p

- PHENIX
- Run 5 200GeV p+p

- (c - J/) Mass (GeV/c2)

- (c - J/) Mass (GeV/c2)

- Run 6 data set has a factor of x3 more luminosity.
*A very tough measurement in AuAu; dAu probably doable.*

## Exotica: More to Come

- Ultra-peripheral Collisions (UPC’s)

- UPC’s : well calibrated
- EM probe
-  measured by STAR
- J/ by PHENIX

## Future

-   Hopefully (PAC willing)....
-      Run 7 & 8: high statistics Au+Au 200GeV, x10 luminosity
-     		high statistics d+Au 200GeV, x10 luminosity

- Detector Upgrades :
- Reaction Plane Detector
- (PHENIX, from Run-7)
- Si Vertex Detector
- (PHENIX and STAR)
- Nosecone Calorimeter, muon
- trigger upgrade, ...

- Longer term:
- RHIC Upgrades:
- Increased luminosity
- Increased species

*And comparisons with STAR results!*

*Then there are also the LHC experiments soon, and the nice results from NA60 (next), *
*so the upcoming few years should be really interesting! *

## Near-Term Future..

*Let’s hope for some nice and friendly semi-final matches*
* **today and tomorrow (9 PM) ! *

## Backup slides

## Heavy quarkonium states, energy levels and radii

- Quarkonium – bound q/q-bar state

## J/ transport model 

- Zhu, Zhuang, Xu, PLB607 (2005) 107
- + private communications

- Au+Au y~1.7 |y| ~ 0

**Adding QGP hydro and J/******** transport ******** better agreement**

**Model includes :**
**Detailed QGP hydro **
**J/****ψ**** ****transport**
**normal nuclear absorption:**
**σ****abs**** = 1 mb **
**σ****abs**** = 3 mb**
**     ****(Curves for y=2 and y=0 are similar)**

## Sequential charmonium dissociation

- Quarkonium dissociation temperatures – Digal, Karsch, Satz

**Karsch, Kharzeev and Satz, hep-ph/0512239**

** ****Based on recent lattice QCD**** calculations, J/******** melting temperature could be higher than initially expected ******** ****suppression of direct J/******** could be out of the range of RHIC**
** ****On the other hand ********c**** and ********’ should melt at a temperature close to T****C**** (~1.1 – 1.2 T****C****)          ******** Anomalous suppression comes from ********c**** and ********’ feed-down.**** **

**H. Satz, Hep-ph/0512217**

**J/******** feed-down :**
** ****~60% from direct production**
** ****~30% ********c**** ******** J/******** + ******
** ****~10% ********’ ******** J/******** + X**

**Overall J/******** survival probability = measured/expected**

**direct J/******** survival probability assume to be 1 at SPS energy**

**Feed-down J/******** survival probablity**

## Sequential charmonium dissociation

** ****J/******** suppression**
** ********’ ****suppression **
** ****but not ********c**

**Karsch, Kharzeev and Satz, hep-ph/0512239**

- SPS data

**(Lattice QCD ******** S********’~S********c****)**

**0.6**

**At RHIC, PHENIX measured :**
** ****J/******** suppression.**

**data are consistent with sequential charmonium dissociation at both RHIC and SPS.**
**Note: Systematic errors ignored..**

- SPS + RHIC data

**Karsch, Kharzeev and Satz, hep-ph/0512239**

**More data needed**

**NA60 preliminary**

**NA60 preliminary**
**PHENIX preliminary**

## Suppression Mechanism

- J/ Suppression Models:
- assume heavy quarkonia are formed only during the initial hard nucleon-nucleon collisions
- Subsequent interactions only result in additional loss of yield
- Color Screening:
- Color charge of one quark masked by the surrounding quarks
- Prevents cc-bar binding in the interaction region
- Characterized by Debye screening radius (rD)
- If the screening radius is smaller than the J/ radius then the quarks are effectively masked from one another

**Notes:**
So, here let me first remind you about the suppression mechanism. In suppression models, the assumption is made that
heavy quarkonia such as the J/psi are first created in the initial nucleon-nucleon collision. And that subsequent interactions only result in a loss of yield.
How does this color screening work then? Color charge of one quark masked by the surrounding quarks and what we call a Debye screening radius. If this radius is smaller than the J/psi radius, then the quarks are effectively masked from each other.  

## RAA vs Npart : Comparison with NA50 data (QM’05)

-    NA50 data is normalized to NA50 p+p point.
-    Suppression level is rather similar between the two experiments, although  the collision energy is 10+ times higher at RHIC (200 GeV vs 17 GeV).
-    Note: size of error bars, or common systematic error band not negligible!

**Notes:**
This is again the same data as on the previous slide but here we plot it vs Npart, which emphasizes the Au and Cu data more. Here we compare it to the curve from NA50. I don’t want to say too much about this but just point out that the suppression pattern is pretty similar. But the size of errors is not negligible so we should probably not draw too far-reaching conclusions on this yet. 

## RAA vs Npart: Comparison with cold nuclear effects (QM05)

- RAA vs Npart: Comparison with cold nuclear effects (QM05)

- Prediction from pQCD calculations, including 3mb nuclear absorption and shadowing.
- Seems to underestimate the suppression somewhat.
- Note: abs somewhat too high wrt d+Au data; Should have
- 1 mb curve also.

- Forward rapidity

- Mid rapidity

**Notes:**
Now we start with the model comparisons.
Here is the same data but now vs a calculation including both absorption and shadowing. We have split up the data into forward and mid-rapidity. This is not such a bad description of the data, but one should bear in mind that the dA data indicated that already 3 mb might be a little large, and the absorption curve should thus probably go a little higher.  

## RAA vs Npart: Comparison with predictions without regeneration 									(QM05)

-   Models which approx. reproduce NA50 data, with J/ suppression only. (no regeneration mechanism)

**Over-estimates J/******** **
**suppression at RHIC!**** **
** **

**Notes:**
A more valid comparison for the energy dependence might be to compare with suppression models which roughly reproduce the NA50 data. They clearly over-estimate the suppression at RHIC.

## RAA vs Npart : Comparison with predictions w. regeneration (QM05)

- Models using suppression + various regeneration mechanisms;

**Better matching with data points, but note that all model calculations should be checked to use up-to-date charm and J/******** p+p cross-sections!**
**(reduced exp. errors on those quantities would also help) **

**Notes:**
So, when we include re-generation, the models generally do a much better job. 
One caveat to note is that most curves and calculations at QM05 times used older charm and J/psi cross section value from Run2, i.e. should be updated. 
[This will move the curves somewhat up.
We will update these curves.]

## The PHENIX detector

- J/e+e-

- J/************

## PHENIX Detector: Muon Arms

- Muon Tracker and Muon Identifier provide good momentum resolution and tracking ability
- High rate level 1 dimuon trigger
- Online level 2 filtering

- Like Sign
- Subtraction

## PHENIX Detector: Central Arm

- Drift Chamber provides high resolution tracking and momentum resolution
- RICH and EmCal provide electron identification
- High rate level 1 electron trigger
- Online level 2 filtering

- Like Sign
- Subtraction

## Silicon Vertex Detector 

- Silicon Vertex Detector

- Four barrel layers
- Two ALICE pixel bus layers
- Two strip-pixel layers
- Four end-cap pixel layers
- Displaced vertex (σ ~50 m)
- Full azimuthal inner tracking |η| < ~2.4
- Improve acceptance for -jet correlations, D  K
- Connect to tracks in central and muon arms
- Tag heavy flavor decays
- c,b  e,
- B  J/
- Improve onium resolution
- Eliminate decay hadrons
- Reduce high-pT background

## Nose Cone Calorimeter

- Replace central arm magnet nosecones (Cu) w/ tungsten-silicon calorimeters
- Coverage at forward/backward rapidity: 0.9 < |η| < 3.5
- /0 separation for *p**T* < 30 GeV/c
- Jet identification
-  identification gives good acceptance for c  J/ + 

## Muon Trigger Upgrade

- Three layers of RPCs with 2D (θ,φ) pad readout
- Provides online momentum measurement to improve Level-1 trigger rejection
- Single-particle
*p**T* cut
*W* spin-measurements in *pp*
- Two-particle
*M**inv* cut
- onium measurements in AA
- Necessary to take complete advantage of luminosity upgrades
- Provides improved high-multiplicity background rejection

## Intermission: Comparison with Other Prompt Probes

- Intermission: Comparison with Other Prompt Probes

- A** general** way to classify QCD probes is by speed and color multiplet; different combinations give rise to different classes of high-Q2 observables:

- (P. Stankus)

**Notes:**
To put this all in context, let’s look at the available pQCD probes we have to understand the medium we create.
A general way to classify QCD probes is by color and speed through the medium.
One class of probes are the slow/heavy color, like open charm, as an energy loss probe.
Another class are the fast probes, resulting in jets.
Then we also have quarkonium and direct photons, as deconfinement and colorless, probes respectively.
[What I will discuss today are the slow and heavy quarkonia. ]

## 

Compare and contrast J/ vs. jets
Initial jet production well understood (pQCD vs data)
Cold nuclear matter effects for jets give RpA > 1 (opposite of signal, easy to disentangle; also have
    direct photons as add’l control.)

Not true for J/’s unfortunately..

- Compare and contrast J/ vs. jets
- Initial jet production well understood (pQCD vs data)
- Cold nuclear matter effects for jets give R*pA* > 1 (opposite of signal, easy to disentangle; also have
-     direct photons as add’l control.)
- Not true for J/’s unfortunately..

*Why is it hard to draw conclusions from the observed J/**** R**AA** ?*

**Notes:**
Let’s do a comparison between J/psi and the high pT / jet physics.

## Jets: AuAu vs. dAu (PHENIX)

**Au + Au Experiment**

**d + Au Control Experiment**

- Preliminary Data

- Final Data

- Phys. Rev. Lett. **91**, 072303 (2003).

**Notes:**
Opposite trends in AuAu and dAu ; separation of normal nuclear effects and what is seen in AA..

## Comparison of leading 0 spectrum (PHENIX) to pQCD

- Phys. Rev. Lett. **91**, 241803 (2003).

**Notes:**
Here you see the data from PHENIX compared with a pQCD calculation. Good agreement.

## Jets Strongly Suppressed at RHIC!

- Photons are not suppressed  initial state production *does* scale with *N**binary*.
- [ From magnitude of jet suppression we are able to quantify the gluon density and this is viewed as one of the cornerstones of the arguments that we have created an sQGP at RHIC. ]

**Notes:**
And then in addition, the high pT  

## 

Other aspects of “rich” J/ physics...
Thermal charm enhancement – not
Charm quark energy loss
Recombination

- Other aspects of “rich” J/ physics...
- Thermal charm enhancement – not
- Charm quark energy loss
- Recombination

## Total Charm Production Scales w/Nbinary

- PPG035
- Phys. Rev. Lett. **94**, 082301 (2005).

- It had been suggested that, in addition to being produced in initial hard-scattering events, charm quarks in RHIC collisions could also be produced via collisions of thermal partons due to the extreme temperatures that would be reached.
- PHENIX data shows that this is apparently not significant.

## But, Charm Quarks Lose Energy in the Medium Created at RHIC

- PPG056
- Phys. Rev. Lett. **96**,
- 032301 (2006).