1. Marzia Rosati mrosati@iastate.edu Iowa State University
Charmonium in Heavy Ion Collisions
Marzia Rosati
Iowa State University
Beijing, China
October 11, 2004

2. Outline Why Heavy Ion Collisions? QCD and the QGP Phase Transition
Quarkonium in Media Measurements at the SPS
New Quarkonium Measurements at RHIC
Future Prospects at RHIC and LHC

3. QCD Lagrangian
The interaction between quarks and gluons can be described by as the coupling “constant” NP
HEP
non perturbative at long range/low energy
asymptotic freedom at short range / high energy

4. QCD Missing Mass Puzzle
The mass terms one inserts into the QCD Lagrangian have ~nothing to do with the observed hadron masses
Each quark has the mass of about 1% of a proton or neutron (!)
md ~ 7 MeV
mu ~ 4 MeV
The origin of the rest (~98%) of the mass is of dynamical origin: it is due to the interactions.
Non-perturbative Vacuum q

5. Gluon field fluctuations
QCD and Confinenement
Non-perturbative Vacuum q
Gluons carry the color charge
 gluons can emit gluons!
qq pairs, gluon loops fill space, “normal vacuum” is not empty!!
Possible correlations between loops  vacuum “superconducting”
QCD color field excluded from vacuum  quarks must stay outside of vacuum and inside hadrons q
Gluon field fluctuations

6. Lattice QCD calculations
Teraflop-scale computers simulate equilibrium QCD
Predict phase transition:
hadrons quark/gluon
(QUARK GLUON PLASMA)
(F. Karsch, hep-lat/ )

7. Where to study the QGP Phase Transition?
Big Bang
Only one chance…
Lattice QCD
Neutron stars
Heavy Ion Colliders

8. What are we doing in Heavy Ion Collisions? Why?
Collide heavy nuclei at the highest possible energies
Au+Au Collisions in URQMD Model
Why?
create Quark Gluon Plasma (QGP) as transient state in heavy ion collisions to study
QCD confinement of quarks to hadrons
How hadrons get their masses

9. Charmonium as a Probe of QGP
Matsui and Satz predicted J/y production suppression in Quark Gluon Plasma because of color screening

10. QCD Potential in vacuum:
Coulomb potential
Confinement
in vacuum:
linear increase with distance, strong attractive force
confinement of quarks to hadrons
in dense and hot matter
screening of color charges (similar to Debye screening in dense atomic matter)
potential vanishes for large distance
deconfinement of quarks
 QGP

11. Successive Melting of Charmonium
rD = mD-1 Debye screening radius
when m> miD, state i is no longer bound
state mD (GeV) TD eD
y’ 0.3 <Tc <ec melts first
c Tc ec melts 2nd
J/y Tc 2ec smallest, hard to screen

12. Quarkonium in QGP
Hadrons with radii greater than ~lD will be dissolved
Study quarkonium bound states

13. Screening by the QGP

14. Heavy Ion Collisions b is large b is small
In a glancing blow or “peripheral” collision, not much of excitement happens.
b is large
In a head on or “central” collision, there is a lot of energy transferred – forming a QGP?
b is small
Impact parameter cannot be measured directly. So experiments have to use a measured quantity as a proxy for impact parameter: multiplicity, total transverse energy, etc…

15. QGP Search with Quarkonium
Peripheral
Collision:
Large impact paramater
Central
Collision:
Small impact parameter

16. Production of J/y
Use J/y and y’ beams to test energy density of matter:
J/y, y’
matter
box ??
medium in box:
A) vacuum no absorption
B) confined low energy density absorption of y’
C) deconfined high energy density absorption of J/y and y’
vary energy density  search for threshold behavior
in J/y and y’ absorption

17. Heavy-Ion Accelerators1 2 3 4
Colliding Nuclei
Hard Collisions
Parton Cascade
Hadron Gas & Freeze-out

18. The NA50 experiment
A closed-geometry muon spectrometer, like many other charmonium experiments.

19. NA50 Measurement Physics: Experiment: Analysis:
Look at J/Y via decay to m+m-
Experiment:
Absorb “all” hadrons before they make muons!
Analysis:
Form spectrum of
Remove “combinatoric background” by subtracting (suitably scaled) like-sign mass spectrum
Absorber
Calorimeter
Spectrometer
Incident Beam
Target(s) m+ m-

20. NA50 in Practice Fits to the mass spectrum are simultaneous fit to:
Background
Open charm
J/Y Y’
Drell-Yan
Absolute yields of J/Y are (were) scaled by that of “Drell-Yan
Yield Scales like A*B
No final state interactions

21. The Plot That Got Everyone Excited
Suppression pattern vs. L is different for Pb-Pb
What is L?
“the mean length of the path of the (cc) system through nuclear matter of mean density r0”
A way to combine different beams, targets and energies
“Anomalous J/Y suppression in Pb-Pb interactions at 158 GeV/c per nucleon”,
Phys. Lett. B410, 337 (1997).

23. J/y and y’ Cross Section versus L
M.C. Abreu et al.,
Phys.Lett. B450 (1999) 456
NA50
anomalous absorption of J/y in Pb-Pb
anomalous absorption of y’ in Pb-Pb and S-U

24. Detailed study of “Normal Nuclear Suppression”
NA50: J/Y and Y’ from p-Be, Al, Cu, Ag, W, Pb
G. Borges, " New Results on J/psi and psiprime nuclear absorption in p-A and S-U collisions at the CERN/SPS "

25. NA50 more recently

26. NA38/50 Summary Plot cc suppression J/y suppression ?
Measured / Expected
J/y suppression ?

27. The story is not so simple!
MATSUI-SATZ: Rplasma screening < Rquarkonium : SUPPRESSION
NA50: Anomalous Suppression
ALTERNATIVES: Dense hadronic medium, comovers
NEW LATTICE RESULTS: Jpsi survives beyond Tc

28. Percolation Model: geometrical transition
H. Satz, M. Nardi
In Central collisions nucleons undergo
several interactions and, since each
collision establishes a string, we will
obtain a spaghetti like of intertwined
overlapping QCD strings.
Deconfinement is expected when there is
enough internetting between nucleons.
Deconfinement is a function of string size
(QCD) and deconfinement string density
hep-ph

29. Dual Parton Model: A. Capella
Na50 J/y suppression can be reproduced by DPM with absorption by comovers. The number of comovers in Capella model is proportional to number of participants and also to number of collisions.
A. Capella, D. Sousa, nucl-th/

30. Multiple ccbar pairs in high energy AA Collisions

31. Statistical coalescence model
A.P.Kostyuk, M.I. Gorenstein, H. Stocker, W. Greiner, Phys. Lett B 531,

32. New Lattice Results (I)
S. Datta, F. Karsch, P. Petreczky, I. Wetzorke, Phys. Rev. D69: (2004)

33. New Lattice Results (II)
M. Asakawa and T. Hatsuda, Phys. Rev. Lett: (2004)

34. Question is Still Open
J/Y in Heavy Ion Collisions is Normal Nuclear Production (pA) scaled up PLUS
Hot hadron gas, comovers
QGP/dense matter modifications to production:
Debye screening,
Enhancement in coalescence models, balancing of D+D↔J/Y+X

35. Charm Production at SPS and RHIC
Increased cross section will make production at RHIC times than at SPS.

36. End