1. Introduction of Heavy Ion Physics at RHIC
Y. Akiba (RIKEN)
Japan Korea PHENIX Collab. meeting
October 19, 2015

2. At RHIC and LHC, we study this hot matter of early Universe
History of the Universe
QGP: Hot soup made of Quarks and Gluons
Nucleons
were formed
Atoms
formed
Stars and Galaxies
~10 msec
160 MeV
2 trillion ℃
Universe was created 13.8B years ago
Early Universe was filled with hot soup of quarks and gluon, Quark-Gluon Plasma (QGP).
About 10 msec after the BIG Bang, quarks and gluons were frozen inside of nucleon
At RHIC and LHC, we study this hot matter of early Universe

3. Re-create Hot matter of Early Universe
In the first 10 msec after the Big Bang, the Universe was filled by hot soup of quarks and gluons, Quark-Gluon Plasma (QGP)
At RHIC and LHC, this hot matter is re-produced by colliding heavy nuclei at high energies.
Nucleons are melted into quark-gluon soup as ice melt to water
Matter at low temperature (T<160 MeV)
Quark Gluon Plasma （ＱＧＰ）
Heating and
compression
At low temperature, quarks and gluons are confined in nuleons
At high temperature, T>160 MeV (~ 2 trillion ℃),
Nucleons are melted into QGP

4. phase transition Quark Gluon Plasma Phase diagram of QCD
Phase diagram of Water
Quark Gluon Plasma T mB
LHC
RHIC
Quark Gluon Plasma
JHEP11(2010) 77
Hadron
Tc ~ 160 MeV; e ~ 1 GeV/fm3
RHIC covers T≲ 2Tc
+ possible critical point
LHC covers T ≲ 3Tc
This is the only phase transition that occurred in the early universe that can be recreated in the lab

5. RHIC at BNL p+p at √s=510 GeV max Au+Au at √s=200 GeV max
Started at Year 2000
collided various beams
pp, pAu, pAl, dAu, He3+Au,
CuCu, CuAu , AuAu, UU
Approx 500 tracks result from a Au+Au ion collision

6. RHIC’s Two Major Discoveries
Strong Elliptic flow
Agree with ideal hydrodynamics
Low viscosity/entropy (h/s)
STAR PRL86,402 (2001)
High pT suppression
Energy loss of quark/gluon
Very dense matter
PHENIX PRL88,022301(2002)
Jet Quenching
Strong elliptic flow
Dense and low viscosity fluid is formed in nuclear collisions at RHIC
These results are confirmed by LHC at higher energy

7. High pT hadron suppression
No energy loss of scattered parton
p+p
p+p
Scattered parton suffered energy loss in QGP
Au+Au
Au+Au
Scaled by Ncoll
Energy Loss
time

8. Strong suppression of high pT pi0 Nuclear Modification factor
2002 data.
Nuclear Modification factor
Au-Au at 200 GeV PRL
Peripheral collisoin
Suppression/enhancement factor relative to binary collisions
N+N baseline
A facor of five suppression at 10 GeV/c
Scattered paron suffer a large energy loss in QGP
Central collision

9. LHC extends RAA to ~100 GeV/c

10. RHIC’s Two Major Discoveries
High pT suppression
Energy loss of quark/gluon
Very dense matter
PHENIX PRL88,022301(2002)
Strong Elliptic flow
Agree with ideal hydrodynamics
Low viscosity/entropy (h/s)
STAR PRL86,402 (2001)
Jet Quenching
Strong elliptic flow
Dense and low viscosity fluid is formed in nuclear collisions at RHIC
These results are confirmed by LHC at higher energy

11. Elliptic Flow Strong flow = very small viscosityx z y
Non Central collision
Reaction Plane
Reaction Plane
High density matter
Beam view of the reaction
Weakly-coupled
large h/s
strongly-coupled
small h/s
Strong flow = very small viscosity
viscosity disturbs the flow
The flow strength v2 is reduced even by a tiny viscosity
In non-central collisions, high density matter with elliptic shape is formed
Expansion towards reaction plane
 Elliptic Flow
V2: the strength of Elliptic Flow

12. ＱＧＰ is a liquid with almost no viscosity
Gas has large specific viscosity  little elliptic flow
Strong elliptic flow indicates that the viscosity of QGP is very small

13. Comparison with viscous hydro
Behavior of the fluid is governed by the sheer viscosity (h) to entropy density (s) ratio h/s
Theoretical work with non-zero viscosity shows that very small h/s ~ 0.1 is required to explain RHIC v2 data
Matter formed at RHIC is almost perfect fluid.
P. Romatschke and U. Romatschke、PRL99,172301(2007)

14. (Almost) perfect liquid
v2 data from RHIC indicates that the high density matter formed at RHIC has very small h/s. The value, h/s ~ 0.1, is 1/10 of all known matter, and it is close to the lower bound 1/4p conjectured by AdS/CFT model
4p×h/s N2 He
H2O
Quark Gluon Plasma
1012 0C

15. Triangular flow ｖ３ Elliptic flow v2 is the 2nd order Fourier component
There are higher order components v3, v4, v5….
Odd order componets v3, v5, etc relative to reaction plane is zero due to symmetry
Event-by-Event Fluctuation of initial geometry cause ｖ３ and higher odd order components.
Initial geometry 3rd order component　e3 causes 3rd order flow v3
V3 is a good probe of initial condition

16. RHIC vs LHC Both RHIC & LHC flow (v2,v3,v4,v5) data are explained
Initial state assumption
Saturated Glasma
MC Glauber
Both RHIC & LHC flow (v2,v3,v4,v5) data are explained
h/s (LHC) ~ 1.6 h/s (RHIC)
Higher order flow study is sensitive to the initial fluctuation

17. Initial temperature of QGP
Hot matter emits thermal radiation
The initial temperature of the QGP can be estimated from measurement of thermal photons

18. Temperature of the Stars

19. Initial temperature via photons
PHENIX PRL104, (2010)
Large enhancement of direct photons at low pT at RHIC
Consistent with thermal radiation with initial temperature of MeV
RHIC Tinit

20. What I didn’t covered Hadron spectra and yield
HBT correlation (infermerometry)
Quarkonia (J/Psi, Upsilon)
Heavy quarks (charm and bottom)
Low mass lepton pairs
Fluctuations
Beam energy dependence
Where is the critical point
and much more…

21. Summary
New phase of matter, QGP, is discovered at RHIC and is confirmed at LHC
QGP is characterized by
Near perfect fluidity
Strong energy loss of parton
This is the only “Phase transition” of quantum field realized at laboratory
Quantitative study of its properties at RHIC and LHC
Quark Gluon Plasma
Temperature
Baryon Density T mB
LHC
RHIC