1. ICPAQGP 2010, Goa, India High-Energy Nuclear Collisions and QCD Phase Structure Nu Xu (1) Nuclear Science Division, Lawrence Berkeley National Laboratory, USA (2) College of Physical Science & Technology, Center China Normal University, China

2. Outline Introduction: Phase Structure of QCD
RHIC beam energy scan: v2, χp
Phase diagrams of QCD: a collection

3. Quantum ChromoDynamicsL
QCD is the basic theory for strong interaction. Its degrees of freedom, are well defined at small distance.
Little is known regarding the dynamical structures of matter that made from q, g. E.g. the confinement, nucleon spin, the QCD phase structure... Large αS and strong coupling – QCD at long distance.

4. Beam Energy Scans at RHIC and LHC
Chemical freeze-out
(tri-)Critical point
LHC:
2.76 – 5.4 TeV (Pb)
(0.9 – 14 TeV (p))
RHIC:
200 – 5 GeV (Au)
FAiR*/NICA:
11 – 4 GeV (Au)
T: 180 – 55 MeV
μB: 5 – 800 MeV

5. (2) RHIC Beam Energy Scan

6. Events taken (Million MB events)
STAR’s BES Plan*
√sNN (GeV)
B(MeV)
Events taken (Million MB events)
5.0
550
5 (?)
Run11
7.7
410 5
Run10
11.5
300
7.5 18
230
100 27
151
150 39
112
250
As low the beam energy as possible in order to cover a wide range.
Marches to corresponding SPS center of mass energy.
Started in Run10 when the new TOF was ready.
* Phase-I. Depends on the out comes, we may have Phase-II BES at more focused region of the beam energy scan

7. STAR Detector
EMC Barrel
MRPC ToF Barrel
HLT
BBC
TPC
FTPC
PMD
Fast DAQ and particle identification over 2p in azimuthal angle in a wide rapidity window.

8. Centrality Determinations
Mid-y dN/dη  collision centrality  Npart, εstd, εpart.
Understand the initial condition is essential!

9. Particle Identification
√sNN = 39 GeV Au + Au Collisions
TPC TPC+ToF
Beam Energy
Timing Resolution
Remarks
200 (GeV)
85 (ps)
At 39 GeV, using a new calibration scheme without information of start time from VPD (Vertex Position Detector), 87 ps of timing resolution has been achieved.
62.4 (GeV)
90 (ps)
39 (GeV)
11.5 & 7.7 (GeV)
~ 80 (ps)

10. Au+Au at 7.7 GeV Au+Au at 39 GeV Au+Au at 200 GeV
PID: 7.7, 39, 200 GeV (π±, K±, p)
Au+Au at 7.7 GeV Au+Au at 39 GeV Au+Au at 200 GeV

11. High Moments: Critical Point Search
Measure conserved quantities, B, s, and Q.
First: High order fluctuation results consistent with thermalization.
First: Tests the long distance QCD predictions in hot/dense medium.
Caveats: (a) static vs. dynamic; (b) net-B vs. net-p; (c) potential effects of freeze-out…
R. Gavai, S. Gupta, / F. Karsch, K. Redlich, / M. Stephanov,
STAR: PRL105, 02232(2010) and references therein.

12. Partonic Collectivity at RHIC
STAR: preliminary
QM09: arXiv
Partonic Collectivity at RHIC!
Session-7: Shi // arXiv // PHENIX: nucl-ex/

13. Number of Quark Scaling in v2
At intermediate pT region, v2-scaling in nq works for π, K, ρ0, p, ϕ, Λ, Ξ, Ω and light nuclei up to 3He.
Coalescence process for hadronization.
 Partonic collectivity and de-confinement.
[STAR Jena: ICPAQGP10]
v2/nq
[STAR Shi: ICPAQGP10]

14. Observable: Quark Scaling 
m ~ mp ~ 1 GeV
ss   not K+K-  
h << p, 
In the hadronic case:
No number of quark scaling
Very small value of  v2 !

15. Results on Anisotropic Flow
ALICE arXie
From Kuma, Mohanty and Shi
Stronger collectivity at LHC!
Initial eccentricity ε is largely uncertain

16. Energy Dependence: K/p Ratio
[Kumar: ICPAQGP2010]
N(K+)/N(p+) ratio vs. √sNN may reflect the degree of baryon stopping, due to the associate process: NN  NΛK+. Important for strangeness production!
√sNN ~ 8 GeV is the max. of freeze-out baryon density.
J. Randrup & J. Cleymans,
Phys. Rev. C 74 (2006)
√sNN~8 GeV

17. Other Observables At each collision energy:
Local parity violation: a three particle correlation measurement
HBT as a function of reaction plane
Directed flow v1
E-by-E N(K)/N(p), N(p)/N(p) ratios
E-by-E <pT>, <Nch>
High moments for net-charge, p, K, p

18. (3) Collection of QCD Phase Diagram

19. RHIC Neutron stars Neutron stars Neutron stars
QCD Phase Diagram (1953)
Neutron stars
E. Fermi: “Notes on Thermodynamics and Statistics ” (1953)

20. QCD Phase Diagram 1983 1983 US Long Range Plan - by Gordon Baym
(1, 2, 5-10)ρ0
1983 US Long Range Plan - by Gordon Baym
TC~200 MeV
(1, 2, 5-10)*ρ0

21. QCD Phase Diagram (2009)
1983 US Long Range Plan - by Gordon Baym
nucl-th: , NPA830,709(09) L. McLerran
nucl-th : A. Andronic, D. Blaschke, P. Braun-Munzinger, J. Cleymans, K. Fukushima, L.D. McLerran,
H. Oeschler, R.D. Pisarski, K. Redlich, C. Sasaki, H. Satz, and J. Stachel
Systematic experimental measurements (Ebeam, A) :
Extract numbers that is related to the QCD phase diagram!

22. Slope Parameter Systematics
Partonic
Hadronic
Student Lecture, “Quark Matter 2006”, Shanghai, Nov , 2006

23. Direct Radiation Measurements
Hadronic
Partonic
Di-leptons allow us to measure the direct radiation from the matter with partonic degrees of freedom, no hadronization!
Low mass region:
, ,   e-e+
minv  e-e+
medium effect
Chiral symmetry(?)
- Intermediate region:
J/  e-e+
Direct radiation
Expanding partonic matter at RHIC and LHC!
Direct
radiation:
hadronic partonic
STAR already started its di-electron measurements!

24. Di-lepton Program at STAR
STAR Preliminary ω ϕ
J/ψ
pT (GeV/c)
Key measurements: yields, mass, RAA, v2  thermalization, thermal rates

25. γ*γ* Interferometry (HBT)
Hadronic
Partonic
[Mohanty: ICAPQGP10]
Virtual gamma HBT sensitive to, due to the off-shell mass, is sensitive to the duration of the source, hence the collectivity as a function of emission time.
The di-leptons sense ‘volume emission’ while hadrons are mostly ‘surface emission’! Leptons: QGP evolution (phase) can be assessed.
P. Mohanty, J. Alam, B. Monhanty, arXiv:

26. D-lepton Signal for QGP Expansion
Hadronic
Partonic
Di-lepton transverse mass slope parameters reflect the sources.
At the intermediate mass region (IMR), partonic phase is dominate, the slope parameter vary smoothly while dramatic effects are seen at the low mass region (M ≤ 1 GeV).
J. Deng, Q. Wang, NX, PF. Zhuang arXiv:

27. Summary
The QCD phase structure  long distance QCD. A serious beam energy scan program, for the search of QCD critical point and phase boundary, has just began.
Next generation of new experiments with high rate capabilities are important for the study of the QCD phase structure around the phase boundary. NA61 at SPS, CBM at FAiR and MPD at NICA.
In order to understand the dynamical evolution from cold nuclear matter to quark gluon plasma in high-energy nuclear collisions, a good understanding of the initial condition is necessary.

28. International Summer School for High-Energy Nuclear Physics*
CPOD2011, Nov. 7-11, 2011
Wuhan, China
(Critical Point and Onset of De-confinement)
International Summer School for
High-Energy Nuclear Physics*
Nov. 1-5, Wuhan, China
*Supported in part by HIC for FAiR

29. Many Thanks to the Organizers!

30. Phase Diagram
QED QCD
Phase Diagram: A map shows that, at given degrees of freedom, how matter organize itself under external conditions.