after the first discoveries at rhic

After the First Discoveries at RHIC

Hideki HamagakiCenter for Nuclear Study (CNS)

University of Tokyo

2008/04/26 After the First Discoveries at RHIC 2

Our knowledge of QCD matter has been limited to the region at T ~ 0 and 0

～ 1

Our knowledge of QCD matter has been limited to the region at T ~ 0 and 0

～ 1

Primary Goal of Study with High-Energy Heavy-Ion Collisions

•Understand hadronic matter under extreme conditions−Basic QCD property; confinement & chiral symmetry−Relevance to Early universe

High-energy heavy-ion collision provides extreme conditions

• Accelerators• Cosmic rays

High-energy heavy-ion collision provides extreme conditions

• Accelerators• Cosmic rays

Phys.Rev. D72 (2005) 034004

2008/04/26 After the First Discoveries at RHIC 3

Accelerators

1970 1980 1990 2000 2010 2020

LBL Bevalac1974~1993ECM=2GeV

BNL AGS1986~ECM=5GeV

CERN SPS1986~ECM=17GeV

BNL RHIC2000~ECM=200GeV

CERN LHC2009~ECM=5500GeV

(GeV)

1000

100

10

1

2008/04/26 After the First Discoveries at RHIC 4

Gross Features of High-Energy Heavy-Ion Collisions

• nuclei = Lorentz contracted disks (d~2R/)• participant-spectator picture works well

– classical trajectory– participant region is geometrically determined

• Specification of ‘Centrality’ is a Must to characterize the collisions Spectator -- beam fragment

Spectator -- target fragment

Participant

2008/04/26 After the First Discoveries at RHIC 5

Initial Processes in High-Energy Heavy-Ion Collisions

• Collisions in high energy– between partons (quarks and gluons) in t

he colliding nucleons

• Two competing processes in the initial stage– hard process

• large-Q2 scattering between partons• pQCD calculation• becomes prominent in high energy

– soft process• dominant in the low-energy collisions• multi-particle production with low-pT• non-perturbative

2008/04/26 After the First Discoveries at RHIC 6

Characteristics of Hard Process

• jet & single photon production• production yield; proportional to number of binary collisions

between nucleons (<- Glauber model)

– with known nuclear effects• Cronin effect• Nuclear shadowing effect

• Nuclear modification factor

pp

coll

AAdp

NdEN

dp

NdE

3

3

3

3Color Glass Condensate (CGC) becomes important at high gluon density; central subject at LHC)

TTppcoll

TTAATAA dppdNN

dppdNpR

2008/04/26 After the First Discoveries at RHIC 7

RHIC and the Experiments

• New York State, USA• Long Island• Brookhaven National Lab.

BRAHMS, PHOBOS • Small collaborations (~100)• Large but small coverage

STAR , PHENIX • Big collaborations (~500)• Small but large coverage

RHIC• 2 independent rings• 3.83 km circumference• CMS energy

– Au + Au: up to 200 A GeV– p + p: 500 GeV (polarized)

• two programs: Heavy Ion and SPIN

2008/04/26 After the First Discoveries at RHIC 8

Japanese group in PHENIX

• Two Japanese groups have been participating in the PHENIX experiment

– Heavy ion: Japan-US collaboration in High Energy Physics– SPIN: RIKEN SPIN project

2008/04/26 After the First Discoveries at RHIC 9

RHIC Physics Runs• RUN-1: June ~ Sep.4, 2000

Au+Au: (sNN)1/2 = 132 GeV• RUN-2: Aug. 2001 ~ Jan. 2002

Au+Au, p+p: (sNN)1/2 = 200 GeV• RUN-3: Jan. 2003 ~ May 2004

d+Au, p+p ： (sNN)1/2 = 200 GeV• RUN-4: Jan. 2004 ~ May 2004

Au+Au, p+p: (sNN)1/2 = 200, 63 GeV• RUN-5: Jan. 2005 ~May 2005

Cu+Cu: (sNN)1/2 = 200, 63 GeV

p+p: (s)1/2 = 200 GeV• RUN-6: Feb. 2006 ~June 2006

p+p: (s)1/2 = 200 GeV, 63 GeV• RUN-7: Mar. 2007~June 2007

Au+Au, p+p: (sNN)1/2 = 200 GeV• RUN-8: Nov.29 2007~Mar. 2008

d+Au, p+p: (sNN)1/2 = 200 GeV,...

First Au + Au collisions at √sNN = 56 GeVJune 12, 2000

2008/04/26 After the First Discoveries at RHIC 10

The First Major Discovery at RHIC• Strong suppression of pion yie

ld at high-pT in central Au+Au collisions– most high-pT pions are from jet f

ragmentation

• Strong jet energy loss >>> Evidence of formation of hi

gh-density matter

Energy loss in plasma

p p

Hot dense medium

TTppcoll

TTAATAA dppdNN

dppdNpR

2008/04/26 After the First Discoveries at RHIC 11

The Second Major Discovery at RHIC

• Large anisotropy in angular distribution in azimuth – hydro-dynamical behavior ~ consistent with hydro with

no viscosity => perfect liquid

React

ion

plan

e

Spatial anisotropy --->>> Momentum anisotropy

2008/04/26 After the First Discoveries at RHIC 12

Top Story 2005

According to American Institut of Physics, the top physics story in 2005 was the discovery of the perfect liquid

2008/04/26 After the First Discoveries at RHIC 13

Where has all the energy gone?

• Collective excitation, analogous to shock wave? --- having been sought since BEVALAC era

4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig

STAR, PRL 90 (2003) 082302

Leadinghadrons

Medium

2008/04/26 After the First Discoveries at RHIC 14

Sideward Particle Emission

• Clear change from back-to-back correlation to sideward correlation with increase of centrality

PHENIX preliminary

2008/04/26 After the First Discoveries at RHIC 15

12

1

3

0

Event by event deflection of jets

1

3

12

0

Cone like structure in each event

Origin of Sideward Peak

• Jet deflection• Cone-like structure

3-particle correlation data by STAR indicates cone-like particle emission

12

1

3

2008/04/26 After the First Discoveries at RHIC 16

3-Particle Correlations at PHENIX

*

Cone Jet

Deflected Jet

Normal Jet

(medium excitation)

(scattered jet axis)

(unmodified)

PHENIX Preliminary

*

High pT (1)

Assoc. pTs (2,3)

Same Side

Away Side

*

*12

*13

* _=

*12

=

2008/04/26 After the First Discoveries at RHIC 17

Trying to Reproduce Mach Cone in Hot QCD Matter

Relevant dynamical quantities:• g2Q projectile color charge• mD screening mass• cs

2 (= dp/d) sound speed– p = /3 -> cs

2 = 1/3

• s = 4/3sT: attentuation length– s = (4/3)(1/4)(1/T) = 1/3T

QM08: B. Mueller, M. Asakawa, R.B. Neufeld, C. Nonaka , J. Ruppert

2008/04/26 After the First Discoveries at RHIC 18

(( 44

• Conjectured lower quantum limit – Derived first in (P. Kovtun, D.T. Son, A.O. Starinets, Phys. Rev. Lett.

94:111601, 2005) – AdS/CFT (Anti de Sitter space / Conformal Field Theory) correspond

ence (J. Maldacena: Adv. Theor. Math. Phys. 2, 231, 1998)

Perfect Fluids?

4

s

• “ordinary” fluids– water (at normal conditions)

• /s ~ 380 ћ/4– helium (at point)

• /s ~ 9 ћ/4

• Need observables that are sensitive to shear stress• Damping (flow, fluctuations, heavy quark motion) ~ /s

2008/04/26 After the First Discoveries at RHIC 19

Heavy Flavor• Production of charm (and bottom) is a

hard process– leading order at low x = ’’gluon fusion’’– Ncoll scaling should hold, with known n

uclear effects of nuclear shadowing and kT broadening

• Interaction is considered to be weaker– gluon bremsstrahlung is suppressed at

forward angles (dead cone effect); < mQ/EQ

• How to measure– “exclusive” is favorable, but difficult in h

eavy ion collisions– semi-leptonic decay measure electro

ns/muons

QQ

22QQ

2 ])/([

1

Em

2008/04/26 After the First Discoveries at RHIC 20

In Au+Au Collisions at sNN = 200 GeVPhys.Rev.Lett.98:172301,2007

• Binary scaling of total e± yield from heavy-flavor decays– Expected from heavy-quark production via hard scattering

• High pT e± suppression increasing with centrality– Energy loss

2008/04/26 After the First Discoveries at RHIC 21

RAA and v2 of non-photonic Electrons

• At pT > 4 GeV/c – b/(c+b) > 0.5– RAA continues dropping– (New) v2 result stays high

-> bottom seems to interact strongly as charm

... need further study to make it quantitative

Large yield suppression and significant v2

2008/04/26 After the First Discoveries at RHIC 22

Viscosity from Heavy Flavor Data• Strongly suppressed & significan

t v2 implies high density & small diffusion coefficient

• DHQx2T ~ 4-6– Rapp & van Hees (PRC 71,

034907 (2005))

• D ~ 6 /(e+P)– Moore & Teaney (PRC 71, 064904

(2005))

• e+P = Ts at B = 0 --> /s = (1.3-2.0)/4= Very close to conjectured lim

itPHENIX : PRL98, 172301 (2007)

2008/04/26 After the First Discoveries at RHIC 23

4/)8.30.1(/ s

S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006

pTfluctuations STAR

Compilation of Estimates 4/)2.12.01.1(/ s

R. Lacey et al.: PRL 98:092301, 2007

v2 PHENIX & STAR

4/)4.24.1(/ s

H.-J. Drescher et al.: arXiv:0704.3553

v2 PHOBOS

conjectured quantum limit

• Estimates of /s based on flow and fluctuation data– Indicate small value as well– Close to conjectured limit– Significantly below /s of heliu

m (s ~ 9)

2008/04/26 After the First Discoveries at RHIC 24

Summary

• First major discoveries at RHIC– Parton energy loss -- high density matter– Hydrodynamical flow -- perfect liquid(?)

• Many interesting results afterward– Mach cone-like structure -- shock wave?– Energy-loss and thermalization of heavy flavor– Anomalous baryon/meson ratio -- recombination pictur

e– Thermal photons in p-p & HI collisions– Low-mass lepton-pairs in HI collisions– Charm to bottom ratio– J/ systematics

2008/04/26 After the First Discoveries at RHIC 25

Outlook

• Good d + Au run in RUN8 -- we will soon have high-statistics results for cold nuclear matter effect

• Au + Au run for low-mass e+e- pairs with HBD (PHENIX)

• Charm and bottom identification with VTX silicon tracker

• Energy scan (to lower energy) for critical point search

• SPIN PROGRAM -- G and W

Backups

2008/04/26 After the First Discoveries at RHIC 27

CMS energy

Initial energy density

Why do we need Higher Energy?

With collisions at higher energy• High initial energy density

– Large margin at RHIC and LHC– Longer duration time of QGP

• Description of space-time evolution becomes simpler– Higher particle density shorter mean free path

• chemical & thermal equilibrium– Hydro-dynamical description may

become possible comparison with models

becomes reliable• Availability of hard probes

– jet & hard photon – heavy flavor

2008/04/26 After the First Discoveries at RHIC 28

Nuclear Effects

• Cronin effectpA(pT) = pp(pT) A(p

T)

(pT) > 1 in the high pT

– small-angle multiple scattering of partons in the initial stage

– kT broadening

• Nuclear shadowing– modification of parton

structure function in case of nuclei

– large depletion in small x

2008/04/26 After the First Discoveries at RHIC 29

Soft Process• non-perturbative phenomenological

description• string model

– confinement potential x with string tension ~ 1 GeV/fm

• Bjorken’s picture– Boost invariance space-time

evolution is determined by proper time

• string trajectory = hyperbola

– string fragmentation at a certain proper time particle production

z

t

0

mT

r02A2/30

dNdy

1r0

2A2/30

dET

dy