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

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

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

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

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

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

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

Strong suppression of high pT pi0 Nuclear Modification factor 2002 data. Nuclear Modification factor Au-Au at 200 GeV PRL91 072301 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

LHC extends RAA to ~100 GeV/c

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

Elliptic Flow Strong flow = very small viscosity x 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

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

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)

(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

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

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

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

Temperature of the Stars

Initial temperature via photons PHENIX PRL104, 132391 (2010) Large enhancement of direct photons at low pT at RHIC Consistent with thermal radiation with initial temperature of 300-600 MeV RHIC Tinit

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…

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