# Presentation: 102169

## Heavy quarkonium and color screening 

- Dmitri Kharzeev
- BNL

- Strongly coupled plasmas, RIKEN-BNL, December 16-17, 2004

## Outline

- QCD and asymptotic freedom
- Heavy quarkonium -
-     the hydrogen atom of QCD
- Strongly coupled QGP
- Heavy quarkonium in sQGP

## Constituents of matter

## Quarks and the Standard Model

- Charm and bottom
- quarks are heavy
- on typical QCD scale
- of ~ 200 MeV,
- and live long enough
- to form bound states
- (charmonium and
- bottomonium)

## “November revoluton”

- The discovery of quarkonium

## Heavy quarkonium

- Why is heavy quarkonium
- so narrow?

## QCD and the “dark mass” of the proton

- QCD = Quark Model + Gauge Invariance

- .i

- Classical scale, UA(1) symmetries
- broken by quantum effects

- Invariant under scale (

- ) and chiral (left <-> right)

- transformations in the limit of massless quarks (u, d)

- Experiment: quarks are almost massless...
-    ... but then... all hadrons must be massless as well!

- Where does the “dark mass” of the proton come from?

## QCD and quantum anomalies

- HHHi

- Classical scale invariance is broken by quantum effects:
- renormalization introduces a dimensionful parameter,
- and gives birth to scale anomaly

- Hadrons get masses              coupling runs with the distance

## Asymptotic Freedom

- At short distances,
- the strong force becomes weak -
- anti-screening
- Gross, Wilczek; Politzer ‘74
- Heavy quarkonia are small,
-           R ~ 1/ (M g2),
- so should be possible to describe
- by weak coupling methods

## Coulomb potential in QCD

- Spectral representation in the t-channel:

- If physical particles can be produced (positive spectral density),
- then unitarity implies screening

- Gluons   Quarks
- (transverse)

## Coulomb potential in QCD - II

- Missing non-Abelian effect: instantaneous Coulomb exchange
- dressed by (zero modes of) transverse gluons

- Negative sign
- (the shift of the ground level
- due to perturbations - unstable vacuum! ):

- Anti-screening

- Gribov ‘78
- Review:
- Yu.Dokshitzer & DK,
- hep-ph/0404216

## Screening in Quark-Gluon Plasma

- These diagrams are enhanced at finite temperature:
- (scattering off thermal gluons and quarks)

- This diagram is not:

- => At high enough T, screening wins

## Screening in the QGP

- F.Karsch, P.Petreczky et al

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

## Strongly coupled QCD plasma

- C. Bernard, T.Blum, ...
-                           F. Karsch, P.Petreczky, ..

- Interactions are important!
- (the “dark mass” of
- the Quark-Gluon Plasma)

## Heavy quarkonium as a probe

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

## Gluo-effect: quarkonium ionization

- Confined phase - soft gluons
-                 (mostly at small x)
- Deconfined phase - hard gluons
-                                 k ~ 3 T
-                                                 DK, H.Satz ‘94
-                   effective “gluo-effect”
-                   ionization

- DK, H.Satz, hep-ph/9505345

- E.Shuryak ‘78

## What mechanism is more important?

- DK, H.Satz, hep-ph/9505345

- Strongly coupled regime:
- E/T >> 1
- Ionization
- Weakly coupled regime:
- E/T << 1
- Screening

## What mechanism is more important?

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

- Weak coupling:

- Strong coupling:

## Heavy quark internal energy above T

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

## Heavy quarkonia above Tc

- M.Asakawa,
- T.Hatsuda

- F.Karsch,
- P.Petreczky,
- K.Petrov,
- F.Zantow, ...

## Experimental information

- CERN: NA38/50/60 experiments

- NA50 Coll., hep-ex/0412036

## Experimental information

- RHIC@BNL: PHENIX experiment

- NA50 Coll., hep-ex/0412036

## Experimental information

- RHIC@BNL: PHENIX experiment

**PRC 69, 014901 (2004)**

## Summary 

- 1. Heavy quarkonium is an excellent probe
- of the deconfinement phase transition
- 2. Detailed information available from
-     the lattice calculations
- 3. Experimental evidence of quarkonium
-     suppression in nuclear collisions at SPS
-     and RHIC
- 4. Good theoretical understanding lacking