High-Energy Nuclear Collisions& the QCD Phase Structure
Nu Xu(1,2)(1) College of Physical Science and Technology, Central China Normal University, Wuhan, China(2) Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, USA

Many Thanks to the Organizers!
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

1/38

Quantum ChromoDynamics

ShortdistanceLongdistance

1) QCD is the basic theory for strong interaction. Its degrees offreedom, are well defined at short distance.
2) Little is known regarding the dynamical structures of matter thatmade from q, g. E.g. the confinement, nucleon spin, the QCD phasestructure... Large αS and strong coupling – QCD at long distance.
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

2/38

What Is the Problem ?
- The confinement:
Quarks are the basic building blocks of matter.
No free quarks are seen, confined within hadron:Δv0 ~ 1 fm3, ρ0 ~ 0.16 fm-3, ε0 ~ 0.15 GeV/fm3- Heavy ion collisions: Large, hot and dense systemphase structure
T.D Lee, 1970
Δv ~ 1000 fm3 = 1000 v0
ρ >> 3 fm-3
~ 20 ρ0Quark Gluon Plasma (QGP)3ε >> 3 GeV/fm ~ 20 ε0⇒Quarks and gluons are ‘freely’ moving in a large volume
New form of matter with partonic degrees of freedom- Connection with other fields
cosmology, origin of the universe, evolution of the universe,
quantum statistics with partons, …
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

3/38

The QCD Phase Diagram andHigh-Energy Nuclear Collisions
Tini, TC
LHC,LHCRHICSPS

21.5

TE RHIC,SPS,FAIRAGS
SIS

RHIC

1213Phase boundary
RHIC, FAIR, NICA

quark-gluon plasma

FAIR/NICA

3icaemCh

0.5

lt*-ouzee
freTemperature T/TC

1

hadronic phase002468Baryon Chemical Potential µB/TC

Phase Diagram: Water
Phase diagram: A map showsthat, at given degrees offreedom, how matter organize
itself under externalconditions.
Water: H2O
The QCD phase diagram:structure of matter with quarkand gluon-degrees (colordegrees) of freedom.

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

5/38

QCD Diagram (1953)
E. Fermi: “Notes on Thermodynamics and Statistics ” (1953)

E. Fermi

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

6/38

QCD Diagram (1983)
1983 US Long Range Plan - by Gordon BaymGordon Baym

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

7/38

QCD Diagram (2009)
Happy Island?

Larry McLerrannucl-th: 0907.4489, NPA830,709(09) L. McLerrannucl-th 0911.4806: A. Andronic, D. Blaschke, P. BraunMunzinger, J. Cleymans, K. Fukushima, L.D.
McLerran, H. Oeschler, R.D. Pisarski, K. Redlich, C.
Sasaki, H. Satz, and J. Stach

Systematic experimental measurements vs. (Ebeam, Asize):
extract numbers that related to the QCD phase diagram!
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

8/38

Outline(1) Introduction(2) Recent results from RHIC
(3) RHIC Beam Energy Scan
(4) Summary

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

9/38

PHOBOS"PHENIX"

RHIC!

BRAHMS"STAR"- RHIC: The high-energy
heavy-ion collider(i) Dedicated QCD colliderAGS!

(ii) √sNN = 200 - 5 GeV(iii) U, Pb, Au, Cu, dAu, pAu- RHIC: The highest energy
polarized proton collider!
TANDEMS!

√s = 200, 500 GeV
Animation M. Lisa

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

10/38

STAR Detectors Fast and Full azimuthal particle identification
EMC+EEMC+FMS(-1 ≤ η ≤ 4)

MRPC Time Of FlightSTAR-China project

TimeProjection
Chamber

Muon
Telescope
Detector 2013
DAQ1000

Heavy
FlavorTracker
2013

BNL PAC, 21 - 22, 2010

Forward
GEM
Tracker
2011

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

11/38

Energy Loss in A+A Collisions
leading particle suppressedback-to-back jets disappear

p+p

Au + Au

Nuclear Modification Factor:

1 d 2σ AA /dpT dy
RAA ( pT ) =2 nn
TAA d σ /dpT dy
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

12/38

Hadron Suppression at RHIC

Hadron suppression in more central Au+Au collisions!
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

13/38

Partonic Energy Loss at RHIC
STAR: Nucl. Phys. A757, 102(2005).

Central Au+Au collisions at √sNN = 200 GeV: light quark
hadrons and the away-side jet in back-to-back ‘jets’ aresuppressed. Major difference from p+p and d+Au collisions.
Energy density at RHIC: ε > 5 GeV/fm3 ~ 30ε0Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

14/38

Anisotropy Parameter v2
coordinate-space-anisotropyy➪momentum-space-anisotropy
pypxx〈 y2 − x2〉
ε= 2〈 y + x2〉

−1v 2 = cos2ϕ , ϕ = tan (pypx)

Initial/final conditions, EoS, degrees of freedom€Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

15/38

System Size Driven Collectivity
sNN = 200 GeV Collisions at RHIC

0.5v2 ⁄ (nq " !part{2})Cu + Cu
0-20%
20-60%

Au + Au
40-80% 10-40% 0-10%0KS
#0.4
0.3
0.2

Npart!part {2}326 ± 6

0.12 ± 0.01

173 ± 100.30 ± 0.01

87 ± 20.24 ± 0.01

42 ± 70.53 ± 0.02

34 ± 10.47 ± 0.02

STAR: PRC81, 44902(10)0.1
Glauber initial conditions

000.5

1

1.52(mT - m) ⁄ nq (GeV/c2)

Collectivity:
Driven by number of participantsMore Analysis: How and when local equilibrium reachedNu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

16/38

Collectivity, De-confinement at RHIC
- v2 of light hadrons andmulti-strange hadrons- scaling by the numberof quarks
At RHIC:➪ nq-scaling
novel hadronization
process➪ Partonic flow
De-confinementiii

PHENIX: PRL91, 182301(03)STAR: PRL92, 052302(04), 95, 122301(05)nucl-ex/0405022, QM05
S. Voloshin, NPA715, 379(03)Models: Greco et al, PRC68, 034904(03)Chen, Ko, nucl-th/0602025
Nonaka et al. PLB583, 73(04)
X. Dong, et al., Phys. Lett. B597, 328(04).
….

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

17/38

Partonic Collectivity at RHIC%%

$sNN = 200 GeV

197

Au+(a) Light quarks(b) Strange quarks

PHENIX: nucl-ex/0604011

STAR: preliminary

20v2 (%)

Au Collisions at RHIC
QM09: arXiv 0907.2265

25

197

QM 0907.2265

1510"!
p5#0012345 012

345

Transverse Momentum pT (GeV/c)//DreamPlot1: partonic collectivity//

Low p (≤ 2 GeV/c): hydrodynamic mass ordering
High pT (> 2 GeV/c): number of quarks ordering//01Run7/Omega_v2/plot1_v2_2apeil09.kumac//T Collectivity developed at partonic stage!
 De-confinement in Au+Au collisions at RHIC!
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

18/38

Hydrodynamic Model Comparison

 Small value of specific viscosity over entropy η/s Model uncertainty dominated by initial eccentricity εModel: Song et al. arXiv:1011.2783
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

19/38

Low η/s at RHIC: “Perfect Liquid”

RHIC results1) Nuclear matter: the viscosity/entropy ratio ≤ 1/4π, the quantum limit.
2) “Strongly interaction matter, small η/s - Perfect liquid” at RHIC.
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

20/38

Antimatter Discoveries at RHIC
April, 2011

“Observation of theAntimatter Helium-4 Nucleus”
by STAR Collaboration
Nature, 473, 353(2011).

Nu XuMarch, 2010

“Observation of anAntimatter Hypernucleus”
by STAR Collaboration
Science, 328, 58(2010).

RGW, August 22 – September 9, 2011, YITP, Kyoto

21/38Summary I(1) In high-energy nuclear collisions, hot anddense matter, with partonic degrees offreedom and collectivity, is formed(2) The matter behavior like a quantum
liquid with very small η/s(3) Partonic matter  antimatter: H e, H e3Λ4What is the structure€of the matter?
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

22/38

Beam Energy Scan at RHIC
Motivations: Study QCD phasestructure- Signals of phase boundary- Signals for critical point

Observations:(1) v2 - NCQ scaling:
partonic vs. hadronic dof(2) Dynamical correlations:partonic vs. hadronic dof(3) Azimuthally HBT:
1st order phase transition(4) Fluctuations:
Critical point, correl. length(5) Directed flow v1
1st order phase transition- http://drupal.star.bnl.gov/STAR/starnotes/public/sn0493- arXiv:1007.2613

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

23/38

Observable*: NCQ Scaling in v2➠➠

AMPT, Au+Au, 9.2GeV, b<14fm, |$|<10.10.08

v2/nq0.06!

#KsK"p(a) Default(b) String MeltingDisappearance of the v2NCQ scaling:

0.04
0.02
000.5

11.5 00.511.5

In the hadronic case, no numberof quark scaling and the value ofv2 of φ will be small.

(m -m0)/nq (GeV/c2)
T* Thermalization is assumed!

STAR Collaboration: F. Liu, S.S. Shi, K.J. Wu et al.
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

24/38

Particle and Anti-Particle v2 vs. √sNN
STAR Preliminary

STAR Preliminary

STAR Preliminary

STAR: QM2011

Below √sNN = 11.5 GeV:v2( baryon) > v2(anti-baryon) and v2( π+) < v2(π-)
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

25/38

v2 Scaling vs. Beam Energy
39 GeVSTAR Preliminary

STAR Preliminary

STAR Preliminary

STAR Preliminary

11.5 GeV

The φ v2 falls off trend from other hadrons at 11.5 GeV
STAR: QM2011
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

26/38

Summary II: v2-NCQ-Scaling
1) Partonic collectivity in 200 GeV collisions2) At √sNN = 11.5 GeV- v2(baryon) > v2(anti-baryon)- v2(ϕ) < v2(hadron) v2-NCQ-scaling broken
 [hadronic] < √sNN = 11.5 GeV√sNN = 39 GeV < [partonic]
Where is the critical point?
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

27/38

Susceptibilities and Moments
Thermodynamic function:

The susceptibility: Tn −4(n )qχ⎛ T µq ⎞1∂n= 4P⎜ , ⎟,T ∂ µ /T n ⎝ TC T ⎠ T /T c(q)q = B,Q,S1
δN q
VT 32(2) € 1
χ q = 3 δN qVT(4 )χqT 2 (2) = κσ 2χq31(3)χ q = 3 δN qVTχ (3)qT (2) = Sσχqχq(1) =( )( )

χ(4 )
q

42 2 ⎞1 ⎛
=− 3 δN q⎜ δN q⎟VT 3 ⎝⎠( )( )

Thermodynamic function  Susceptibility  Moments, Observable€

Model calculations, e.g. LGT, HRG  Measurements

Correlations, Susceptibilities
Higher Moments
δN = N − N(δN ) 2 ≈ ξ 2 ,4(δN ) 3 ≈ ξ 4.5(δN ) − 3 (δN )2 2≈ξ

7M. A. Stephanov, PRL. 102, 032301 (09)S=(δN ) 3(δN )2 3/24

κ=(δN ) − 3 (δN )
(δN )

2 2

2 2

R.V. Gavai and S. Gupta: 1001.2796.
F. Karsch and K. Redlich, arXiv:1007.2581€Skewness: Symmetry of thecorrelation function.
Kurtosis: Peakness of thecorrelation function. Connection
to thermodynamics, χX.
Higher order correlations arecorrespond to higher power ofthe correlation length of thesystem: more sensitive tocritical phenomena.
S & K observables:
total charge, total protons,net-p, net-Q

Non-Gaussian Fluctuations
N: event by event multiplicity distributionm= N

σ=(N − N )s=2

κ=(N − N )s>03

σ3(N − N )4σ4€

For a Gaussian distribution,the skewness and kurtosis
are all zero.
Ideal probe of the nonGaussian fluctuations at€
critical point.
Nu Xu

s<0−3

κ >0
κ <0κ =0€

RGW, August 22 – September 9, 2011, YITP, Kyoto

30/38

Net-proton Higher Moments
STAR: 1004.4959, PRL105, 22303(2010)

Energy Scan in Au+Au collision :Run 10: 7.7, 11.5, 39 GeV
Run 11: 19.6, 27 GeV
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

31/38

Few Remarks
STAR: PRL105,22302(2010)

1) The data is from centrality averaged
events. In this analysis, effects ofvolume and detecting efficiencies
are all canceled out.
2) ALL transport model results values
are higher than unity, except theTheminator result at 200GeV. LGT
predicted values around 0.8-0.9,
due to finite chemical potentialeffect.
3) Test of thermalization with higher
moments.

Energy scan in Au+Au collision :Run 10: 7.7, 11.5, 39 GeV
Run 11: 19.6, 27 GeV
Nu Xu

4) Critical point effect: nonmonotonical dependence oncollision energy.
••

STAR: PRL105, 22302(2010).
F. Karsch and K. Redlich, arXiv:1007.2581

RGW, August 22 – September 9, 2011, YITP, Kyoto

32/38

Thermalization in HI Collisions?

All HI results from are consistent with the thermal model
predictions, except the elementary p+p collisions.
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

33/38

Comparing with LGT Results

References:- STAR, PRL105, 22303(10)- F. Karsch and K. Redlich, PLB695, 136(11)- R.V. Gavai and S. Gupta: PLB696, 459(11)Assumptions:(a) Freeze-out temperature is close to LGT TC(b) Thermal equilibrium reached in central collisions(c) Taylor expansions, at µB≠0, on LGT results are valid

 Lattice results are consistent with data for 60 < √sNN < 200 GeV
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

34/38

Scale of Hot/Dense Matter on LGTJune, 2011

“Scale for thePhase Diagram ofQuantum
Chromodynamics”

Science, 332, 1525(2011)

1) In central collisions at RHIC, the high moments measurements areconsistent with thermal equilibrium assumption2) Scale of LGT, determined with the data, is: TC=175+1-7 (MeV)
STAR, PRL105, 22303(2010); F. Karsch and K. Redlich, PLB695, 136(2011); R.V. Gavai and S. Gupta:
PLB696, 459(2011); S. Gupta, X.F. Luo, B. Mohanty, H.G. Ritter, NX, Science, 332, 1525(2011)
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

35/38

Lattice-QCD: Phase Transitions

Tcconf ~170 MeV

Nu Xu

Tcchiral ~150MeV

RGW, August 22 – September 9, 2011, YITP, Kyoto

36/38

Summary(1) In high-energy nuclear collisions, hot anddense matter, with partonic degrees offreedom and collectivity, is formed(2) The matter behavior like a quantum liquid withvery small η/s(3) Partonic matter  antimatter:3Λ

4H e, H e(4) [partonic] < µB ~ 110–320 (MeV) < [hadronic](5) Net-proton distributions are consistent with LGT+1 (MeV)
results. QCD Scale: T€=175C-7

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

37/38

Summary & Outlook
1Tini, TC
LHC,LHCRHICSPS

21.5

TE RHIC,SPS,FAIRAGSSISRHIC

13icaemCh

0.5

lt*-ouzeefreTemperature T/TC

2Phase boundary
RHIC, FAIR, NICA

quark-gluon plasma

FAIR/NICA

13hadronic phase002468Baryon Chemical Potential µB/TC
Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

38/38

Many Thanks to theOrganizers!

Student Lecture, “Quark Matter 2006”, Shanghai, Nov. 14 - 20, 2006
Nu Xu

Nu Xu

RGW, August 22 – September 9, 2011, YITP, Kyoto

40/59

40/38