1. Quark Gluon Plasma and Heavy Ion Collisions
Ginés MARTINEZ
Subatech, Nantes
5th France-China Particle Physics Laboratory Workshop
March 21st -24th 2012, Orsay-Saclay, France

2. Phase Diagram of Matter
QGP
Liquid
Water

3. Plan of the talk Introduction. Quark Gluon Plasma.
Golden probes of the QGP.
Heavy Ion Collisions.
Biased summary of experimental results at RHIC and at the LHC.
Conclusions.

4. Hagedorn limit temperature
W. Broniowski et al., PRD 70,117503(2004)
TH is the Hagedorn temperature
When matter try to reach the TH temperature, energy is used to increase the number of hadronic resonances;
In consequence, infinite energy will be needed to reach a temperature TH (~170 MeV) of matter;
TH is the limit temperature of the matter.
R. Hagedorn, Nuovo Cimento Supplemento vol.3, page 147 (1965)

5. Asymptotic freedom 1st diagrams of vacuum polarization
Nobel Prize in Physics 2004
&

6. PRL (1975)
PLB (1975)

7. Hadronic Matter in 1975
Deconfined phase
PLB (1975)

8. (naïve) Quark Gluon Plasma
Ultra relativistic ideal gas
Stephan-Boltzmann law for bosons and fermions respectively
g=2 for photons, g=4 for leptons (e, m), g=3 for p, g=16 for gluons and 18 for quarks (u, d, s),
In natural units
Degrees of freedom in QGP larger than in Hadron Gas

9. Chiral Symmetry breaking
QCD Lagrangian of massless Quarks
Quark helicity is well defined
Invariant under Chiral symmetry transformations
The Chiral symmetry is spontaneously broken
Massless goldstone bosons exist: the light hadron: pion, kaon
Chiral symmetry is restored at high energy or T
Masses of the pion, kaon ≠ 0 : Quark are not exactly massless (u,d,s). Chiral symmetry is explicitly broken
Phase transition (or cross-over) should take place
Decofinement (m=∞) and Chiral transition are the same in QCD (confirmed by lattice QCD)

10. Analogy : Ferromagnetic transition
Chiral
Ferromagnetic
Spontaneously broken
SU(3)LxSU(3)R
Isotropie O(4)
Order Parameter
Condensate <qq>≠0
Magnetisation≠0
Waves
Goldstone bosons: p, K, h
Spin waves
Explicitly broken
Mass of the quarks
External Magnetic field
T. Schaefer hep-ph/

11. Lattice QCD calculations
mB=0
Not latest lQCD results!
Many discussions on critical temperature.
Not addressed here!
Hadron Gas to QGP phase transition

12. Crossover vs phase transition
Not latest lQCD results!

13. Hadronic Matter in 2012
mB=0
lQCD
mB≠0 lQCD in progress & Models

14. Golden “probes” of QGP Thermal radiation from QGP.
Heavy quark potential in QGP.
Parton-QGP interaction.

15. Thermal Radiation Golden probe to measure the temperature of the QGP;
It can be real (g production) or virtual (g*=>e+e_) dielectron production;
Note that black-body thermal radiation is a bad approximation for a QGP of 7 fm diameter since the mean path of a photon or lepton in QGP will be larger that its diameter. Yields scale by a factor aQED/aQCD~0.02 (at GeV scale).;

16. Quarkonium Bound state of Q and its anti-Q:
Charmonium for c-cbar: J/y, y’, cc;
Bottomonium for b-bar: upsilon family 1S, 2S and 3S.
Properly described by Quark Model
Charmonium family

17. Colour screening V(r) a exp(-r/lD)/r, lD a 1/rg, rg increases with T
Heavy Quark potential is screened
Quarkonium melts
V(r) a exp(-r/lD)/r, lD a 1/rg, rg increases with T

18. Colour Screening of heavy Quark V(r)
Colour charges in the QGP could screen the potential between two heavy quarks:
Only if lD(Debye Length)<RQQ(size of the quarkonum) screening occurs;
lD depends on QGP temperature.

19. Parton-QGP interaction
Depending on colour density in the QGP;
Casimir factor (CR): 4/3 for q , 3 for g
Dead cone effect: important for beauty 5 GeV/c2

20. More fundamental QCD questions
q,g
How lost-energy is dissipated in the medium?
How partons fragment in the medium?
Flavour dependence?

21. Experimental Method
Heating matter with Ultra Relativistic Heavy Ion Collisions.
The first problems to be solved:
More complex than an incoherent superposition of individual parton-parton (nucleon-nucleon) collisions.
Full Thermal and Chemical Equilibration of the system.
Nuclear Dynamics under control
Looking for Probes of the equilibrated and highly excited matter.

22. ?

23. QGP and Heavy Ion Collisions
A-A collisions ( Au-Au, Pb-Pb, etc…);
Large Lorentz factor (g>10, sqrt(s)>17 GeV);
Number of binary NN collisions ~ 1000;
tcrois >> tQCD ~ 1 fm/c
Parton parton interactions
Bjorken PRD (1983)
Bjorken Scenario
Bjorken PRD (1983)

24. QGP and Heavy Ion Collisions
A+A collisions ( Au-Au, Pb-Pb, etc…);
Large Lorentz factor (g>10, sqrt(s)>17 GeV);
Number of binary NN collisions ~ 1000;
At LHC, e0~10-40 GeV/fm3, Ti~ MeV
Generation of transverse energy
Beginning of longitudinal expansion
Hydro-dynamical evolution
e0 =
d<ET> dy
p R2 tform 1
Bjorken PRD (1983)

25. QGP and Heavy Ion Collisions
A+A collisions ( Au-Au, Pb-Pb, etc…);
Large Lorentz factor (g>10, sqrt(s)>17 GeV);
Number of binary NN collisions ~ 1000;
At LHC, e0~10-40 GeV/fm3, Ti~ MeV
e/e0 ~ (t0/t)4/3
Longitudinal expansion
in QGP phase!
End of longitudinal expansion
Beginning 3D expansion

26. QGP and Heavy Ion Collisions
A+A collisions ( Au-Au, Pb-Pb, etc…);
Large Lorentz factor (g>10, sqrt(s)>17 GeV);
Number of binary NN collisions ~ 1000;
At LHC, e0~10-40 GeV/fm3, Ti~ MeV
Freeze-out
e/T4 ~ 1.2
Rfreeze ~ fm

27. Heavy Ion Facilities SPS Heavy Ion accelerator (1986-):
Pb, In at 158A GeV, O, S at 200A GeV on fixed target;
NA35,WA80, CERES, WA98, NA50, NA49, NA57, NA60..
RHIC, BNL ( ?):
Au+Au at 62, 130, 200A GeV, d+Au at 200 GeV, p+p at 200GeV and Cu+Cu at 62 and 200A GeV;
PHENIX, STAR, PHOBOS, BRAHMS;
LHC, CERN ( ?):
PbPb at 2.76A TeV, 5.5A TeV;
ALICE, CMS, ATLAS;

28. Super Proton Synchroton SPS
160A GeV Pb Beam
for physics
√s ~ 17A GeV
West Area
WAXX experiment (Switzerland)
North Area
NAXX experiment (France)
SPS Tunnel
CERN, Geneva
SPS is the LHC injector …

29. Relativistic Heavy Ion Collider
3.83 km circumference
Two separated rings
120 bunches/ring
106 ns bunch crossing time
A+A, p+A, p+p
Maximum Beam Energy :
500 GeV for p+p
200A GeV for Au+Au
Luminosity
Au+Au: 2 x 1026 cm-2 s-1
p+p : 2 x 1032 cm-2 s-1
Mid-rapidity at 90o
Interaction Point
BNL, Upton, Long Island, New York

30. RHIC Accelerator Elements
Tandem Van de Graaff
Au- to Au+12, Au+32 1A MeV
AGS
Alternating Gradient Synchroton
Au+77 to Au+79
9A GeV
Booster
Au+32 to Au+77
~90A MeV
RHIC
Relativistic Heavy Ion Collider
Au+79+Au+79
100A GeV

31. Large Hadron Collider PbPb collisions at 5.5A TeV ( x30 step );
Luminosity 1027 cm-2 s-1;
Limited by physics;
QGP: hotter, bigger and longer;
Baryon free matter;
Large production cross-section of hard (penetrating) probes;

32. Interaction Points 4 experiments: ATLAS (Higgs, new physics, QGP);
CMS (Higgs,new physics , QGP);
LHCb (Anti-matter, new physics);
ALICE (QGP, new physics);

34. Penetrating (QGP) Probes : Photons, Dileptons, Jets and Heavy Quarks.
Probes of QGP
Global Probes: Multiplicity, Centrality dependence, transverse energy, …
Hadronic Phase Probes (freeze-out): hadron yields, hadron y and pT distributions, elliptic flow, HBT hadron correlations, Hadron resonances, vector mesons …
Penetrating (QGP) Probes : Photons, Dileptons, Jets and Heavy Quarks.

35. Results from HIC at RHIC & LHC
My personal summary of experimental data on heavy ion collisions at RHIC and LHC. Many results will not be presented. Surely my view is biased and you must be aware of it.

36. Initial Energy Density at RHIC
Phys. Rev. C 71, (2005)
Bjorken Model:
Au+Au at 200 GeV
eBj ~ 5-10 GeV/fm3

37. Initial Energy Density at LHC
PRL 105, (2010)
Pb+Pb at 2.76 TeV; eBj ~ GeV/fm3; Assumed mean pT increase of 30%; t0 assumed to be constant.

38. Statistical Hadronization at RHIC
Chemical freeze-out:
Two parameters: Tch and mB;
Tch ~ 164 MeV;
mB ;~ 22 MeV
Phys. Lett. B 697 (2011) 203 [arXiv: ]
System seems to thermalize before freee-out.

39. Statistical Hadronization at LHC
arXiv: v1
LHC should be the ultimate test. mB~0 and similar Temperature than at RHIC.

40. Elliptic Flow in Heavy Ions
From Mark D. Baker presentation (BNL)

41. Elliptic Flow (v2) at RHIC
STAR coll., PRC72(2005)014904
Elliptic flow is important in HIC;
Well understood at RHIC with Hydrodynamical models;
sQGP (ideal fluid) concept has been suggested;

42. QGP characterization at RHIC
Systems thermalizes quickly:
Challenge from the theory to explain this. Not thermalized gluon-ball called glasma, would thermalize and would create a QGPn short time scales (1 fm/c);
QGP initial temperature about 2Tc and it expands following relativistic hydro-dynamics.
It behaves as an ideal fluid with a shear viscosity (1<4p(h/s)QGP<2.5). Extremely strong interaction between partons in the QGP.
Song H, Bass SA, Heinz U, Hirano T, Shen C, Phys. Rev. Lett. 109, (2011), arXiv:

43. Elliptic Flow at LHC
Phys. Rev. Lett. 105, (2010)
Similar than at RHIC, but higher mean pT, so 30% increase of pT integrated v2

44. Direct Photon Excess at RHIC
Direct photon excess above p+p spectrum.
Exponential (consistent with thermal).
Inverse slope = 220 ± 20 MeV.
Ti from hydro.
MeV.
Depending on thermalization time.
NLO Vogelsang
√sNN = 200 GeV
Au+Au
min. bias
p+p
PRL 104, (2010)

45. Nuclear Modification Factor
Nuclear thickness TAA is evaluated via a Glauber model.
TAA x sNN represent the number of NN collisions in the heavy ion reaction.
A priori, if not final interaction with QCD medium RAA=1.

46. High pT suppression at RHIC
B. A. Cole, summary talk in QM2008

47. Charged Hadron RAA at LHC
Berndt Mueller, Juergen Schukraft and Bolesław Wysłouch arXiv: v1

48. Dijet analysis in CMS
CMS coll. arXiv:

49. Dijet analysis in ATLAS
Peter Steinberg for ATLAS coll. , QM2001

50. Xiaoming ZHANG, J. Phys. G. 38 (2011) 124067
Open Heavy Flavour
ALICE coll. arXiv: v1
Charm hadron RAA suppression is observed in Pb-Pb at 2.76 TeV.
Comparable to light hadron suppression.
Suppression of muon from heavy flavour decay is also observed.
Muons are produced namely by B mesons decays.
More results very soon …
Xiaoming ZHANG, J. Phys. G. 38 (2011)

51. J/ψ suppression in HIC SPS NA50 SPS NA60 RHIC
T.M & H. S. J/y suppression by quark-gluon plasma, PLB178, 416 (1986)
J/ψ suppression in HIC
SPS NA50
SPS NA60
RHIC
Suppression observed (~40%);
y’ suppression also measured;
Drell-Yan relative normalization;
Cold nuclear matter (CNM) absorption correction;
Colour screening models worked;
Other approaches (comover interaction, statistical models) not ruled out.
Absorption cross-section in cold nuclear matter is not constant;
Suppression still there (~20-30%);
CNM nightmare (absorption, shadowing …);
Only colour screening dissociation of y’ and cc?
Suppression observed (~40-80%);
Less suppression at high pT;
Larger suppression at large rapidity;
Nuclear modification factor normalization;
CNM nightmare (absorption, shadowing, energy-loss);
Recombination mechanism needed by colour screening models;
Statistical production explains the data.
NA50
NA60
PHENIX
R. Arnaldi (NA60), arXiv: v2,
Nucl. Phys. A830, 345c (2009)
NA50, Eur. Phys. J. C39, 335 (2005)
PHENIX, arXiv: v1 (2011)
Quantitative conclusions missing. Open charm crucial. Other quarkonium species.

52. J/y RAA 0.2 / 2.76 TeV J/y mm, pT>0
ALICE collaboration arXiv: v1
CERN Courier, March 2012 vol 52 Issue 2
J/y mm, pT>0
J/y RAA larger at LHC (2.5<y<4) than at RHIC (1.2<|y|<2.2); Similar as RHIC (|y|<0.35), except for the most central bin; dNch/dh(Npart)LHC ~ 2.1 x dNch/dh(Npart)RHIC.

53. J/ψ RAA and shadowing
ALICE collaboration arXiv: v1
Shadowing is expected to increase from RHIC to LHC

54. Low versus High pT J/y
Courtesy of C. Suire (IPNO)
ALICE coll. arXiv: v1 and CMS coll. arXiv: v1
High pT J/y more suppressed than low pT J/y at LHC . Not observed at RHIC

55. Upsilon suppression at LHC
CMS coll. arXiv: v1

56. Conclusions
QGP properties are being studied at RHIC and LHC colliders.
At RHIC energies, QGP behaves as a ideal fluid, exhibits a high colour density, and it is formed at T above 300 MeV.
At LHC energies, initial energy densities are a factor ~3 higher (15-26 GeV/fm3) than that at RHIC (30% higher T).
First measurements at LHC indicates similar patterns than at RHIC.
In addition, jet quenching decrease at high pT and jet quenching is also observed at LHC in the di-jet channel.
Intriguing hints have been found in the quarkonium measurements at LHC, suggesting differences to the observation at RHIC.
New era for QGP started in 2010 at LHC. Rapid progress on the characterization of the QGP in the next years.

57. QGP at LHC : more data needed.
A mathematician, a physicist, and an engineer were travelling through Scotland when they saw a black sheep through the window of the train. "Aha," says the engineer, "I see that Scottish sheep are black.” "Hmm," says the physicist, "You mean that some Scottish sheep are black.” "No," says the mathematician, "All we know is that there is at least one sheep in Scotland, and that at least one side of that one sheep is black!” “Fermat’s Enigma” by Simon Singh