# Presentation: 654357

## J/ and Open Charm Production in Heavy Ion Collisions

- Vince Cianciolo, ORNL
- DNP’03 Workshop on QCD, Confinement and Heavy Ion Physics
- 10/29/2003

**Notes:**
I have the rather daunting task of covering all of J/psi and open charm production in heavy ion collisions. 
And to my way of thinking such a talk would be incomplete w/o discussion of pp and pA collisions, so I’ll try to be efficient.

## Outline

- Motivation
- Why heavy ion collisions?
- Why J/ and charm?
- Experimental Basics
- Collision geometry
- NA38/NA50, E772/E866, PHENIX overview
- Open charm production
- Closed charm production
- Outlook

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

## 

Motivation

- Motivation

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- DNP'03 Workshop 10/29/2003

## Re-creating the Big Bang in the Lab

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
My favorite analogy for heavy ion collisions is a time machine. For a brief moment after the Big Bang we believe that quarks and gluons roamed free. As the universe cooled they were frozen inside protons and neutrons, which shortly afterwards fused into light ions. The many exciting results on the CMB come from a view of the universe when it finally became transparent to light some 300000 years after that as the universe cooled enough for atoms to form. And here we are today, hearing about attempts to recreate those conditions in the lab.

## Connecting Quarks with the Cosmos...

- Stolen from title of 2001 National Research Council Report by the Committee on the Physics of the Universe:
- “Connecting Quarks with the Cosmos:
- Eleven Science Questions for the New Century”

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- DNP'03 Workshop 10/29/2003

**Notes:**
I’m not creative enough to come up with this slide title... It was stolen from... The study of RHIC collisions attempts to answer question number 7
You know this is big news when it makes the cover of Discover magazine.

## But Why Heavy Ions?

- The highest energy densities are achieved in e+e- collisions.
- Energy density is not enough.
- Heavy ion collisions provide sufficient energy density over a “large” volume.
- Conditions for a phase transition must prevail for a length of time sufficient for created particles to probe these conditions.
- Heavy ion collisions are not enough.
- Detailed knowledge of our expectations if a phase transition is not achieved is necessary for proper interpretation  of heavy ion collision results (a “control” experiment).
- pp, pA and aa collisions are also needed.

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

## 

Experimental Basics

- Experimental Basics

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- DNP'03 Workshop 10/29/2003

## Pixar View of a Heavy Ion Collision

- Henning Weber,
- UrQMD, Frankfurt

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
In this movie, two Lorentz-contracted nuclei will collide, exploding into a zoo of particles, beautifully illustrating m = E/c^2.

## For sNN = 200 GeV AuAu heavy-on collisions dN/dY ~ 600.
For scale - this is somewhere between 350 and 1000 simultaneous proton-proton collisions!
Beauty is in the eye of the beholder - some would call this a mess!

- For sNN = 200 GeV AuAu heavy-on collisions dN/dY ~ 600.
- For scale - this is somewhere between 350 and 1000 simultaneous proton-proton collisions!
- Beauty is in the eye of the beholder - some would call this a mess!

- Detector Views of a Heavy Ion Collision

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
Such a collision results in a charged particle density of 600 per unit of rapidity. For scale... These events are viewed by 4 detectors at RHIC: STAR, PHENIX, PHOBOS and BRAHMS. For the first three I was able to pull event displays off the web and show them here. To me they are very aesthetically pleasing, but I suppose that beauty...
I’m not sure if it’s because of the spooky costumes my kids are running around the house in or what, but as I assembled this slide I was struck by the fact that the STAR display also kind of looks like a sinister eye. I think an orange version made it into “The Lord of the Rings” as the eye of Sauron. 

## Slide 10

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
Starting from that this is my attempt to make up for the fact that I’ll be missing the pumpkin carving this year.

## Space-time View of a Heavy Ion Collision

- Not only is it difficult to measure these collisions, it is also difficult to interpret them.
- Most of the collision products are hadronic in nature. The strong interaction is strong enough that they will re-interact prior to leaving the collision zone.
- To have mfp > 10fm @  = 200,  < 0.35 mb.
- Note, this “problem” can be a virtue: “jet suppression” analyses rely on jets interacting with and probing the created medium.

- time

- Example trajectory

- z

- QGP

- Mixed
- Phase

- Hadronization

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- DNP'03 Workshop 10/29/2003

**Notes:**
Not only ...
This space-time diagram shows the two nuclei colliding. The primary collisions occur during the nuclear overlap shown in green. Particles made in this region propagate out and through the created medium.
Most of...
Note...

## Matsui and Satz (Phys. Lett. B178, 416.) first articulated the consequences of color screening on quarkonium production.
 c,c-bar pairs are primarily produced through gluon fusion early in the collision.
Most often the c and c-bar quarks pair off with a light quark and exit the system as D-mesons.
Occasionally the c and c-bar pair up with their primordial partner. Due to the attractive strong-force potential they can form bound states like the J/through a non-perturbative process.
If the bound state is formed in, or passes through, a QGP, the free color charges will screen that potential (in a manner completely analogous to Debye screening in a Coulomb plasma).
In this case the J/ will melt (or never form in the first place) and the c and c-bar quarks will again leave the system as D-mesons, having found a ubiquitous light quark.

- Matsui and Satz (Phys. Lett. **B178, **416.) first articulated the consequences of color screening on quarkonium production.
-  c,c-bar pairs are primarily produced through gluon fusion early in the collision.
- Most often the c and c-bar quarks pair off with a light quark and exit the system as D-mesons.
- Occasionally the c and c-bar pair up with their primordial partner. Due to the attractive strong-force potential they can form bound states like the J/through a non-perturbative process.
- If the bound state is formed in, or passes through, a QGP, the free color charges will screen that potential (in a manner completely analogous to Debye screening in a Coulomb plasma).
- In this case the J/ will melt (or never form in the first place) and the c and c-bar quarks will again leave the system as D-mesons, having found a ubiquitous light quark.

- Color Screening and the QGP

- S. Digal, P. Petreczky, H. Satz,
- Phys. Lett. **B514**, 57.

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## An unambiguous signature...

- They carefully outlined the conditions that needed to be met for an observed suppression to be an unambiguous signature of QGP formation.
- We will see that two of these assumptions have turned out to be violated.

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- DNP'03 Workshop 10/29/2003

**Notes:**
They carefully...
We will see...
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.

## 

Experimental Basics

- Experimental Basics

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- DNP'03 Workshop 10/29/2003

## Collision Geometry and Centrality

- For a given impact parameter,
- Glauber model predicts:
- Nbinary  (# binary collisions), and
- Npart (# participants)
- Because the cross-section for a hard-scattering event is small, the probability for any participating nucleon to have two such interactions is very small and such interactions will scale with Nbinary.
- Note: averaging over all centralities Nbinary is the product of the nucleon numbers (AB, or A for pA collisions)
- Soft collisions, on the other hand, are expected to scale as Npart.

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- DNP'03 Workshop 10/29/2003

**Notes:**
This is a generic curve to illustrate the concept of centrality.
The distance between the nuclei is the impact parameter, b. When the impact parameter is large (peripheral collisions) only the edges of two nuclei overlap, the remainder proceed forward undisturbed on the relevant time scale. The overlapping nucleons are participants, the others spectators. As the impact parameter goes down (more central collisions) the number of spectators goes up. Each participant may participate in several nucleon-nucleon collisions, also known as n=binary collisions. This can be seen here – for a central AuAu collision, with 394 participants, there are approximately 1200 binary collisions.

## NA38/NA50

- Toroidal analyzing magnet

- Luminosity monitor

- Segmented active target

- MWPCs, hodoscopes for tracking/triggering

- EmCAL, ZDC, Si-strip multiplicity detector for centrality determination

- Lots of absorber material

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- DNP'03 Workshop 10/29/2003

**Notes:**
The NA38/NA50 apparatus is a classic muon spectrometer. The beam enters from the left. There’s a luminosity monitor, several detectors to measure the collision centrality, lot’s of material to absorb everything but the relatively rare muons, and detectors and magnets for measurement of the particle’s trajectory and momentum and for triggering.

## E772/E866

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
The E772/E866 apparatus is thematically similar, beam entering from the left, lots of absorber material, three analyzing magnets, three tracking stations and some muon identifiers.

## PHENIX

- Two sets of forward-rapidity detectors for event characterization
- Beam-beam counters measure particle production in 3.0<||<3.9. Luminosity monitor + vertex determination.
- Zero-degree calorimeters measure forward-going neutrons.
- Correlation gives centrality

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- DNP'03 Workshop 10/29/2003

**Notes:**
The PHENIX detector is somewhat different in details, but similar in concept.
Two sets...
Two forward... At a collider the muons are relatively low momentum because the center-of-mass is not boosted. This makes the job of separating pions from muons somewhat more challenging than the brute force “more absorber” approach used so successfully in fixed target experiments. A segmented muon identifier is required that distinguishes between pions and muons with an upper momentum cut that depends on the penetration depth.
PHENIX also detects electrons, photons and hadrons at mid-rapidity...

## 

Open Charm Production

- Open Charm Production

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- DNP'03 Workshop 10/29/2003

## Charming Aspects of Heavy Flavor Production

- Production mainly via *gg* fusion in earliest stage of collision.
- Sensitive to initial gluon density.
- Possible additional thermal production at very high temperature.
- Sensitive to initial temperature.
- Energy loss by gluon radiation?  softening of D(B)-meson spectra?
- Sensitive to state of nuclear medium.

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
Charm production is interesting in and of itself.
The production...
There’s also possible ...
This is illustrated in this plot. On the left is shown a prediction for charm production assuming HIJING initial parton densities – here the initial production dominates by more than an order of magnitude. On the right it’s shown that pre-thermal production dominates if the parton densities are in fact four times higher. Dashed lines show the sensitivity to the initial temperature.
It has also been predicted that the energy loss mechanisms for heavy quarks in the medium will be less efficient than they will be for light quarks resulting in a significant enhancement in the D/pi ratio at high-pt.

## Understanding the J/ Baseline

- Drell-Yan (DY) was an appealing J/ normalization process.
- Identical detector acceptance.
- Any deviation expected to signal QGP formation.
- J/ and Open Charm (OC) produced through same initial processes (unlike DY).
- 	 Normalization to OC reduces sensitivity to medium-effects unrelated to screening:
- Shadowing
- Initial state energy loss
- Thermal charm enhancement

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- DNP'03 Workshop 10/29/2003

**Notes:**
Charm production is also a key measurement in our attempts to understand J/psi production.

## Charm Measurements

- Ideal but very challenging
- direct reconstruction of heavy flavor decays (e.g. D0K-+)
- Alternative but indirect
- heavy flavor semi-leptonic decays contribute to single lepton and lepton pair spectra

- PHENIX open charm presentations at DNP

- Sergey Butsyk  (GC.010):  Single Electron Production in pp Collisions 			     (cocktail technique)
- Xinhua Li 	     (GC.011):  Single Electron Production in pp Collisions 			     (e coincidence technique)
- Andrew Glenn   (DG.011):  Single Muon Production in AuAu Collisions
- Ming Liu 	     (CC.004): Single Muon Production in dAu Collisions

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## NA50 – Charm Enhancement?

- NA50 measures charm by looking for di-muon pairs in excess of expectation for  < M < J/.
- For pA collisions they find agreement with PYTHIA scaled by Nbinary.
- For SU and PbPb collisions an excess is observed.

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
This plot shows the charm production cross-section in proton-nucleus and pion-nucleus collisions, scaled by A – the number of binary collisions. The curve is the pythia prediction.
This plot shows their basckground-subtracted di-muon mass plot for PbPb collisions. The contributions to the black curve include Psi, Psi’, Drell-Yan and charm, where the Psi and Psi’ shapes are given by Monte Carlo and normalizations are allowed to float. The prediction falls short of the data in the intermediate mass region. The chramonium and Drell-Yan contributions are rather well fixed, so the possibilities examined are an enhanced charm production and combinatoric backgrounds.

## NA50 – Charm Enhancement? II

- The excess is shown for different PbPb centrality bins with best-fit curves with shapes corresponding to the charm spectrum and the combinatorial background spectrum.
- If all the excess is attributed to additional charm production this excess increases linearly with Npart.

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
This plot shows the excess as a function of invariant mass for different centrality bins. The curves are best fits assuming that the excess is entirely combinatoric background (solid curve) or entirely charm enhancement (dashed). Assuming the entire excess is due to charm enhancement the enhancement factor is plotted versus the number of participants for SU and PbPb collisions and is found to scale linearly. NA50 is careful to state that although the excess is consistent with charm enhancement, other explanations have not been ruled out.

## Light hadron cocktail input:
 0 (dominant source {~80 %} at low pT)
pT spectra from PHENIX 0, ± data                                                                        
Other hadrons
mT scaling:                                                                                                                          
Relative normalization to  at high pT:
 ' (from SPS, FNAL and SPS data) 
 (agrees with STAR’s inclusive /h- = 0.02)                                                                        
Photon conversions
Material in PHENIX acceptance
p dependent conversion probability 
Main systematic errors (band)
Pion spectra
Ratio 0
Ratio conversion/Dalitz (material)
Excess above cocktail, increasing with pT, as expected from charm decays!

-  0 (dominant source {~80 %} at low pT)
*p**T* spectra from PHENIX 0, ± data
- Other hadrons
*m**T* scaling:
- Relative normalization to  at high *p**T*:
-  ' (from SPS, FNAL and SPS data)
-  (agrees with STAR’s inclusive /h- = 0.02)
- Photon conversions
- Material in PHENIX acceptance
*p* dependent conversion probability
- Main systematic errors (band)
- Pion spectra
- Ratio 0
- Ratio conversion/Dalitz (material)
- Excess above cocktail, increasing with *p**T*, as expected from charm decays!

- PHENIX Charm Measurements:Cocktail Method

- PHENIX

- V. Cianciolo

- DNP'03 Workshop 10/29/2003

**Notes:**
This slide illustrates the cocktail method for extracting the charm production cross-section for the 130 GeV AuAu data set.
The pi-zero is the dominant background contributor, both through Dalitz decays and photon conversions – it’s spectrum is taken from PHENIX measurements.
Other hadron spectra are derived from the pi-zero spectrum assuming mt scaling and assigned conservative error bars.
The systematic error band is shown in purple and an excess is observed which increases w/ pt as expected for charm decay.

## sNN = 130 GeV AuAu Single Electron Data

- To quantify the entire excess is attributed to semi-leptonic charm decay, the excess in different centrality bins is integrated and scaled by Nbinary to obtain:
****cc0-10% = 380 ± 60 (stat) ± 200 (sys) b,
- cc0-92% = 420 ± 33 (stat) ± 250 (sys) b

- Compare single electron excess above background with the expected charm contribution by scaling PYTHIA spectra by Nbinary:

- Reasonable agreement over entire spectrum.

- Phys. Rev. Lett. **88**, 192303

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**Notes:**
The subtracted single-electron spectra are shown here. Red points are central events, open points are minimum bias scaled by 100.
The solid curves are PYTHIA predictions for electrons resulting from semi-leptonic decay of charm after scaling by the number of binary collisions.
The dotted and dashed curves are expectations for semi-leptonic decays of bottom mesons and from direct photons. At these pt values both are negligible.
Assuming that the entire excess is due to charm, and assuming binary collision scaling the PYTHIA charm production cross-section is treated as a fit parameter, quantifying the agreement with binary scaling.

## Centrality Dependence

- PHENIX data consistent with the PYTHIA charm spectrum scaled by number of binary collisions in all centrality bins!

- Dominant systematic errors from:
- Using PYTHIA charm spectrum – pp data is being analyzed
- Relying on Monte Carlo for material calculation - special runs 	w/ -converter being analyzed

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**Notes:**
For the 200 GeV data set we can see that this agreement holds in finer centrality bins.
The dominant systematic errors in this analysis are due to... These are being addressed through an analysis of 

## Does Charm Flow at RHIC?

- Previous slides showed that PHENIX open charm data are consistent with PYTHIA scaled by Nbinary
- No interaction with the produced medium.
- It has also been shown that these data are also consistent with the completely opposite dynamical picture
- Zero mean-free-path hydrodynamics

- Batsouli *et al*., Phys. Lett. **B557**, 26

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**Notes:**
This is illustrated in this plot which shows D and B meson spectra from the two models. The resulting electron spectra are indistinguihable.

## Electrons do...

- What is needed to estimate charmed electron flow, v2(c)?
- Charm yield relative to inclusive electron yield at sNN = 200 GeV (r= **N********/N****e**)
- v2() – flow of electrons originating photonic source
- Study v2 D->eX (due to large Q value)

- Shingo Sakai (HC.009)

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**Notes:**
PHENIX is trying to distinguish between these two possibilities by looking for directly for the flow of charm.
As the first step in that effort the flow of electrons has been measured as shown in this plot and as discussed in a presentation later this week.
The electron v2 is made up of both charm v2 and photon v2 contributions. So before the charm v2 can be determined the relative contribution to the electron spectra from charm and photons needs to be determined, as does the photon v2. Finally the correlation between emission angle of the D-meson and the electron must be folded in. 

## Charm in PHENIX Muon Arms

- Single muon production provides information on charm production in a manner similar to the central-arm single-electron production.
- Primary source of background is light hadronic (, K) decay.
- In addition (not shown) hadrons that punch through a part (or all) of the MuID absorber and are subsequently mis-identified as muons are a significant source of background.
- Somewhat trickier than central arm measurement because main sources of background are not directly measured.

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**Notes:**
Single muon production...
The primary... This is shown in this plot which shows the PYTHIA predictions for the relative contributions of muons from light hadron decays (black), open-charm decays (green) and open-bottom decays (red).
In addition...
I’m going to skip over any more details as there aren’t results yet.

## 

J/ production

- J/ production

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## PHENIX J/ Results

- PHENIX J/ presentations at DNP

- Sasha Lebedev      (DG.008)  J/ and c in dAu Collisions
- Xiaorong Wang      (DG.013)  J/ Polarization in pp and dAu Collisions
- Chun Zhang            (DG.007) J/ *x**F** and p**T* Dependence in dAu Collisions
- Sean Kelly              (DG.006) J/   Measurements in PHENIX
- Jane Burward-Hoy (DG.004) J/ Centrality Dependence in dAu Collisions

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## CDF pp (s = 1.8 TeV) results

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

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**Notes:**
It’s rather unnerving (to me at least) that we don’t really understand 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 underpredicts 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.

## PHENIX pp (s = 200 GeV) Results

- PHENIX pp (s = 200 GeV) Results

- J/ seen in both central and muon arms.
- Resolutions in agreement with expectations.

- Run-2: hep-ex/307019

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**Notes:**
For Run-2 J/psi’s were cleanly observed by PHENIX in both the electron and muon spectrometers.
As a sneak preview for the additional statistics from Run-3 I show the mass spectrum from both muon arms – roughly an order of magnitude improvement.

## Rapidity Distribution

- Integrated cross-section : 3.98 ± 0.62 (stat) ± 0.56 (sys) ± 0.41(abs) b
- Estimated B decay feed down contribution : < 4% (@ 200 GeV)
- Some sensitivity to PDFs with additional statistics

- Data: hep-ex/307019
- Curves: H. Sato

- Mc = 1.48 GeV
- Q = 3.1 GeV

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**Notes:**
From the run-2 data we observed comforting consistency between the muon arm and central arm measurements as shown in this plot of the J/psi rapidity distribution. The point at y = 0 is from the central arm, the other points are from the muon arm.
You can see that the rapidity distribution has some sensitivity to the parton distribution functions once more statistics are obtained.

## pT Distribution

*p**T* Distribution

- Combination of electron and muon results gives:
- <*p**T*>  = 1.80 ± 0.23 (stat) ± 0.16 (sys) GeV/c

- hep-ex/307019

- Phenomenological fit A(1+PT/B)2)-6 taken from lower-energy analyses

- Exponential fit

- Color Octet Model calculation doesn’t include fragmentation contributions important for *p**T *> 5 GeV/c

- Color Singlet Model

- Color Singlet Model

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**Notes:**
This plot shows the transverse momentum distributions from the two spectrometers. 
The black curve is a phenomenological fit that works well at fixed-target energies.
The red is an exponential fit.
The blue is the color octet model fit. This calculation does not include fragmentation contributions that start to become significant at higher pt.
The color singlet model again underpredicts the data.
One thing to point out with this data set is the sensitivity down to pT = 0.

## s Scaling

- Phenomenological fit for average pT; p = 0.531, q= 0.188
- Cross-section well described by Color Evaporation Model.

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**Notes:**
This plot shows that the cross-section scales in an expected manner as a function of the center-of mass energy.

## NA38/NA50 pA Results

- Calculate ratio of J/ production to Drell-Yan.
- Many systematic errors cancel in the ratio.
- For each collision type, calculate average length of nuclear material, L, that will pass over the J/.
- Data would be flat if Nbinary scaling was true.
- Glauber model fit to all data yields:

- B. Alessandro *et al*.,
- Phys. Lett. **B553**, 167.

- Note: discontinuity due to different collision energies.

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**Notes:**
NA38 and NA50 studied J/psi production in proton-nucleus collisions. Here they plot the ratio of J/psi’s to Drell-Yan pairs versus a parameter L, which results from a Glauber calculation of the length of nuclear material that will pass over the J/psi.
If the J/psi absorption cross-section were negligible this distribution would be flat.
A Glauber... 

## E772/E866 Results

- _ __X__F__ scaling:_
- J/Ψ and Ψ’ similar at large xF where they both correspond to a cc traversing the nucleus
-  Ψ’ absorbed more strongly than J/Ψ  near mid-rapidity (xF ~ 0) where the resonances are beginning to be hadronized in nucleus
-  Open charm not suppressed (at xF ~ 0)

- _Mass scaling: _
- Power-law scaling observed in pA Collisions: pA = ppA.
-   > 
- DY has  = 1

- M.J. Leitch *et al*.,
- Phys. Rev. Lett. **84**, 3256.

- DM Alde *et al*.,
- Phys. Rev. Lett. **66**, 133;
- Phys. Rev. Lett. **66**, 2285.

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**Notes:**
E772/E866 at FNAL also studied proton-nucleus systematics of J/psi production. 
They quoted their results in terms of a power-law scaling of the cross-section vs. target nucleon number, sigma = Aalpha.
Alpha for upsilon production is large than for j/psi production and no deviation from binary scaling is observed for Drell-Yan production.
They also looked at the Feynman X scaling of alpha. They observed a significant drop at high-XF. Also in this region the value of alpha is the same for Psi and Psi-prime. This behavior is interpreted as evidence for the existence of a precursor state that does not hadronize into the final resonance inside the nucleus due to its Lorentz boost.
At low-XF, where hadronization will start to occur inside the nucleus the psi-prime is more strongly absorbed than the psi. 

## E772/E866 Results, cont.

- _p__T__ scaling:_
- pT broadening is observed
- The shape of  vs. *p**T* is *x**F* independent

- E772: DM Alde *et al*.,
- Phys. Rev. Lett. **66**, 133;
- Phys. Rev. Lett. **66**, 2285.

- E866: M.J. Leitch *et al*.,
- Phys. Rev. Lett. **84**, 3256.

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**Notes:**
Finally they observed a broadening of the transverse momentum distribution with increasing target mass number. This is illustrated by the increasing values for alpha with increasing pT. Again, no such deviations from binary scaling are observed for Drell-Yan production. The shapes of these alpha vs. pt curves are independent of Xf.

## PHENIX dAu Preview

- Enough data to start binning in            centrality, *y*, *xF, pT*, etc.

- Note – efficiencies and acceptances not included  no interpretation possible.

- At RHIC dA collisions are significantly easier than pA (due to *q/M* ratios).

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**Notes:**
RHIC collided deuteron and gold nuclei last year as a reasonable approximation to proton-gold collisions. Analysis is on-going, but I can show you mass spectra to give an idea of the statistical power of the data set. Another way of showing this is to assume some shadowing model and plot its prediction for the ratio of J/psi production in dAu relative to pp as a function of rapidity.  Assuming that the model is correct and knowing the number of counts in the two muon arms we can plot the points and their statistical errors. I should point out that these errors are statistical only.

## NA38/NA50 AA Results

- Absorption only in cold nuclear matter of colliding nuclei cannot explain the data.

- M.C. Abreu *et al*.,
- Phys. Lett. **B450**, 456.

- A. Capella, D. Sousa,
- nucl-th/0303055

- QGP-based models can explain the data.

- Absorption only in cold nuclear matter of colliding nuclei can also explain the data.

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**Notes:**
The NA38 and NA50 results are very well know of course. When the ratio of J/psi to Drell-Yan is corrected for the absorption observed in pA collisions and plotted versus the nuclear thickness parameter L, a distinct suppression is observed.
QGP-inspired models can reproduce this observation.
Unfortunately, so can some models including co-mover absorption as shown here.
To my experimentalist way of thinking, we have made life to easy for the theorists – more data is required to constrain the different models.

## PHENIX AuAu (sNN = 200 GeV) Results

- pp

- Nbinary Scaling

- PHENIX, nucl-ex/0305030

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**Notes:**
The first AuAu J/psi results have come out from PHENIX as shown in this plot of the j/psi cross-section scaled by the number of binary collisions and plotted versus increasing centrality.
The left-most point is the proton-proton result. The other data points are gold-gold results for different centrality bins. The ticks are 1-sigma errors, the ends of the arrows are 90% CLUL’s, the brackets are the 90%CLUL’s with systematic errors included.

The grey band is what would be expected from binary scaling of the proton-proton result, including systematic and statistical errors. 

## Model Comparisons

- No discrimination btwn models w/ suppression w.r.t Nbinary scaling

- Disfavor models w/ enhancement w.r.t Nbinary scaling.

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**Notes:**
This plot shows the same data with some theory curves overlaid.
The lower blue curve is a prediction for absorption by the incoming nuclei and by a QGP.
The upper curve shows that some of the deficit is made up by final-state coalescence of unrelated c and c-bar pairs. Unfortunately this curve is very similar to a curve in the same paper that has only nuclear absorption.
The grey curve is a calculation based on statistical hadronization after complete screening inside a QGP.
The red curves show predictions from the thermal coalescence model with a temperature of 400 MeV and different assumptions about the initial rapidity distribution for the c/c-bar pairs. 
This data set is statistically limiting and nothing can be said about models that predict suppression w.r.t. binary collision scaling.
Even this data set disfavors models that predict enhancement w.r.t binary collision scaling.

## Where do we go from here?

- Broad kinematic reach
- y/pT coverage for open charm, charmonium
- Upsilon may be a good control measurement because it’s more tightly bound  repeat above w/ charm  bottom
- pp collisions
- Initial production mechanism
- pA collisions
- Shadowing
- Initial state energy loss
- Cold medium absorption
- Light ion collisions
- Modify path length through medium
- Most efficient way to dial in Nbinary.
- Energy scans
- Modify energy density
- More difficult (both luminosity & cross-sections fall w/ energy)

- Collect enough data to limit the theorists’ creativity...

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## 

Backup Slides

- Backup Slides

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## PHENIX VTX

- Over the next n years RHIC will provide collisions of many nuclear species at different energies.

- Significant impact on heavy flavor measurements:
- Reduce J/Y backgrounds and improve mass resolution
- Extend open charm, beauty coverage to higher and  lower pT thru DCA cut, direct reconstruction.
- Push structure function measurements to smaller x values.

- In addition to the PHENIX baseline detector a Silicon Vertex Detector (VTX) is being proposed.

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## PHENIX

- Sophisticated multi-level trigger system and pipelined, deadtime-less readout architecture optimized to allow storage of all physics events of interest.
- Data sets include:
- AuAu @ sNN = 130, 200 GeV
- pp @ s = 200 GeV
- dAu @ sNN = 200 GeV

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## Single Muon Backgrounds

- For , K cτ >> 80cm → decay probability nearly constant between nosecones.

- Muons that stop in a particular gap have well-defined momentum.
- Particles with greater momentum are cleanly ID’d as hadrons.
- Some lower-momentum component sneaks in under muon peak.

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## Decay Hadrons

- For decay hadrons a linear behavior is expected in muon the vertex distribution after normalizing for event vertex distribution.
- Indeed, such a behavior is observed and the initial ,K distributions can be deduced used as input to calculate mis-identified hadrons.
- Indirect
- Doesn’t include proton contribution.

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## y,pT Factorization for Hadron Input

- BRAHMS data extracted
- from Djamel Ouerdane’s thesis

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## Comparison with Other Experiments

- Cross sections for:
- single electrons resulting from charm, and
- total charm  production
- are scaled by Nbinary and compared with:
- Solid curves:  PYTHIA
- Shaded band:  NLO QCD

- Assuming Nbinary scaling, PHENIX data are consistent with s systematics  (within  large uncertainties)!
- One of the main systematic uncertainties in this comparison is the pp baseline expectations for charm production, and PHENIX is analyzing these results.

- Phys. Rev. Lett. **88**, 192303

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## sNN = 200 GeV AuAu Single Electron Data

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