# Presentation: 102159

## Heavy quarks in QCD matter

- D. Kharzeev
- BNL

- “Heavy quarks and quarkonia”, BNL, June 6, 2006

## Why heavy quarks?

- .i

- Heavy quark masses MH are generated at the electroweak scale,
- and are external parameters in QCD;
- Heavy quarks are “heavy” because their masses are large
- on the typical QCD scale of QCD:
-                                                          MH >> QCD

## Why heavy quarks?

- .i

- QCD matter is characterized by dimensionful parameters:
- saturation scale QS, density, transport coefficient       , ...

- Use heavy quarks to extract information about
-     the properties of QCD matter

- depending on their values, “heavy” quarks can behave either
- as heavy or as light !

## Why heavy quarkonia?   (I)

- .i

- Heavy quarkonia are characterized by the size
- and the binding energy
- 
- Even though MH >> QCD , the inverse radius and
- the binding energy are not large enough to justify an entirely perturbative treatment even for bottomonium;
- Heavy quakonia are thus a valuable source of
- knowledge about non-perturbative QCD
- (... and a source of trouble for the models aimed at
- describing their production mechanisms ... )

## Why heavy quarkonia?    (II)

- .i

- Heavy quarkonia are very sensitive to the properties
- of QCD matter; when Debye length becomes smaller
- than the size of quarkonium,
-             RDebye(T) ~ 1/(gT) <  RQuarkonium ~ 1 / (s MH ),
- quarkonia are screened out of existence   T. Matsui & H. Satz ‘86
- this happens when T ~ g MH
- (what is the corresponding formula for strong coupling?)
- However, even before that, when T ~ ~ s2 MH,
- quarkonia will be dissociated due to thermal activation

## Why heavy quarkonia?    (III)

- .i

- In cold matter, dissociation rate is relatively small due to
- the softness of gluon distributions in confined matter,
- but it is large, O(1 fm-1), in hot QCD matter
-                                                                               DK & H. Satz ‘94
- Dissociation mechanism - gluo-effect
-                                                                                                     E.Shuryak ‘78
-                                                                                                    G.Bhanot, M.Peskin ‘79
- dominates if                         (strong coupling regime)
- Screening dominates if                     (weak coupling)

## What mechanism is more important?

- DK, L.McLerran, H.Satz
- hep-ph/9504338

- Weak coupling:

- Strong coupling:

## Time evolution in heavy ion collisions

- T. Ludlam,
- L. McLerran,
- Physics Today
- October 2003

## Heavy quarks and the Color Glass Condensate

- .i

- In CGC, heavy quarks can behave either as “light” or “heavy”
- Naïve consideration:
-                                                            DK & K. Tuchin, hep-ph/0310358
-  CGC is characterized by the chromo-electric field
- when the strength of the field is

-  or

- heavy quarks no longer decouple => they are not really “heavy”

- Talk by R.Venugopalan

## J/production in the Color Glass Condensate

- DK, K.Tuchin,
- hep-ph/0510358

## J/production in the Color Glass Condensate

- Data: PHENIX Coll., nucl-ex/0507032
- DK, K.Tuchin, hep-ph/0510358

- “xF scaling”

## Quarkonium in the hadron gas

- DK, nucl-th/9601029
- H.Fujii,DK, hep-ph/9903495

- Quarkonium-hadron scattering amplitude

- can be expressed through the matrix element of the trace of
- the energy-momentum tensor:

- Therefore, the coupling of heavy quarkonium to hadrons at low energy
- is analogous to the coupling of the Higgs boson -

- it is proportional to the hadron mass (squared); decoupling of pions!

## Quarkonium in hadron gas:recent lattice results

- K.Yokokawa, S.Sasaki,
- T.Hatsuda,A.Hayashigaki,
- hep-lat/0605009

- Pion “decoupling” seen in the data!  J/is safe in the pion gas

## Strongly coupled QGP

- F.Karsch et al

- T-dependence of
- the running coupling
- develops in the NP-region
- at T < 3 Tc

## Heavy quarkonium as a probe

- the link between the observables
- and the McLerran-Svetitsky
- confinement criterion

- F.Karsch

## Heavy quark internal energy above T

- O.Kaczmarek, F. Karsch, P.Petreczky,
- F. Zantow, hep-lat/0309121

- Remnants
- of confinement?

## J/ above Tc: alive and well?

- M.Asakawa,
- T.Hatsuda

- S.Datta,
- F.Karsch,
- P.Petreczky,
- I.Wetzorke

## Difficulties of the potential model

- P. Petreczky,
- Mocsy,
- hep-ph/0606053

- Potential model is based on the assumption
- that the interaction is instantaneous, or
- at least much faster than the typical revolution
- time of heavy quarks in quarkonium, 
- OK for the Coulomb potential;
- Fails for soft vacuum fields;
- Probably fails for the screened gluon exchange as well

- Lattice

- Potential

## Heavy quark potential in QCD

- Quark-antiquark interaction energy:

- where

- Subtract quark self-interaction energy; get

- Compute the integral:

- Coulomb potential; why such a complicated derivation?

## Is confinement a “short-distance”phenomenon? 

- r

- r’

- Potential between the heavy quarks:

- The color electric field at a large distance:

- Introduce a cut-off at R; the resulting potential is

- Confining, but quadratic - not linear!

- V.Zakharov

## Is confinement a “short-distance”phenomenon? 

- Potential in the Operator Product Expansion:

- Confining, but: quadratic, not linear!
- OPE sums leading large-distance contributions;
- _are we missing an important short-distance non-perturbative physics?_
- If yes, it would not be immediately screened away above Tc...

- Perhaps, infrared-finite
- QCD coupling?
- “Coulomb confinement” ?
- => Linear confining potential

- e.g., Dokshitzer, DK, hep-ph/0404216

## J/suppression at RHIC

- “same as at SPS”?

## Sequential charmonium dissociation?

- Both the absence of J/suppression up to ~ 2 Tc in
- the lattice QCD data and
- the apparent similarity of the magnitude of suppression
- at RHIC and SPS are puzzling;
- However, the two puzzles may be consistent with each other

- F.Karsch, DK, H.Satz,
- hep-ph/0512239

## Is there  a “direct” J/suppression at SPS?

- ~ 40%
- of observed
- J/‘s
- originate
- from and 
- decays;
- they should
- be gone above Tc

## Is there  a “direct” J/suppression at RHIC?

- Data: PHENIX, NA50, NA60

- Energy density at the time
- J/is formed -
- assumed = 1 fm/c

## Transverse momentum distributions

- Glauber model
- analysis

- “Secondary” J/’s
- have softer pT
- distributions +
- Cronin effect =>
- suppression mostly
- at small pT

## Recombination of charm quarks?

- R.Thews

- Recombination narrows the rapidity distribution; is this seen?
- Are high p_t charmonia suppressed stronger than open charm?

## Summary

- 20 years after, the problem of J/behavior
-      in quark-gluon plasma (and color glass
-      condensate) remains in the focus of attention
- This problem may well keep the key to
-      understanding the strongly coupled plasma,
-      much like the surprising properties of J/
-      were central to understanding QCD
-            More work has to be done...