Heavy-Ion Collisions at RHIC~Search for Quark Gluon Plasma~

Takao SakaguchiBrookhaven National Laboratory

米国ブルックヘブン国立研究所 　坂口貴男

Outline of talk•Motivation of Quark Gluon Plasma Search•Accelerator and detectors•Dynamics and Global feature of Heavy ion collisions•Hard scattering as a new probe•Direct Photon, Jet and Heavy Quark results•Summary and Future

Why do we carry out Heavy Ion Collisions?

Why Quark Gluon Plasma (QGP) ?• Believe it or not!

• It existed in the early universe.

• Understanding fundamental QCD problem• Quark confinement• Origin of proton (hadron) Mas

s• Both questions rely on ｌ ow

Q2 region, where s(Q2)>1

• QGP is a phase where bare strong interaction plays significant role• Quarks and gluons are free fr

om hadron “bag”• Study dynamical behavior of s

trongly interacting system

STAR Solenoidal field

Large Solid Angle TrackingTPC’s, Si-Vertex Tracking

RICH, EM Cal, TOF

Measurements of Hadronic observables using a large acceptance spectrometer

Event-by-event analyses of global observables, hadronic spectra and jets

PHENIXAxial Field

High Resolution & Rates2 Central Arms, 2 Forward Arms TEC, RICH, EM Cal, Si, TOF, -ID

Leptons, Photons, and Hadrons in selected solid angles (especially muons)

Simultaneous detection of phase transition phenomena (e– coincidences)

PHOBOS“Table-top” 2 Arm Spectrometer Magnet,

Si -Strips, Si Multiplicity Rings, TOF

Low pt charged hadronsMultiplicity in 4 & Particle Correlations

Ring Counters

Paddle Trigger Counter

Spectrometer

TOF

Octagon+Vertex

BRAHMS2 Spectrometers - fixed target geometryMagnets, Tracking Chambers, TOF, RICH

Inclusive particle production over a large rapidity and pt range

RHIC at BNLLong Island, New York

Run started in 2000. Around 6 months running every year. Statistics aka PHENIX experiment.

Species s1/2 [GeV ] Ldt Ntot (sampled) Data Size

Au+Au 130 1 b-1 10M 3 TB

Au+Au 200 265 b-1 1.8G 120 TB

Au+Au 63 9.1 b-1 58M 4 TB

p+p 200 0.5 pb-1 10G 50 TB

d+Au 200 2.74 nb-1 5.5G 46 TB

Cu+Cu 200 3.06 nb-1 1.1G

Cu+Cu 63 0.16 nb-1

•First Heavy Ion collider•3.83 km circumference•106 ns bunch crossing•Top Energy:

•500 GeV for p+p•200 GeV for Au+Au

•Luminosity•Au+Au: 2 x 1026 cm-2 s-

1

• p+p : 2 x 1032 cm-2 s-1

　 (polarized)

Time profile of heavy ion collisions

• Gold ions “pass through” each other• Large-x partons fly over.• Mid-rapidity region is full of small-x gluons

• High energy heavy ion collisions = Gluonic matter collisions

• Turns into Gluon plasma

• Gluon -> quark + anti-quark -> QGP

• Cooling QGP -> Mixed phase -> Hadronic stage

• Global Feature• Energy density: 5.7GeV/fm3 @ Au+Au sNN

=200GeV (ref. LQCD: reaches plateau at 2-3GeV/fm3)

• Temperature T=178MeV (Threshold)

Gluon Plasma QGP phase Mixed phase Hadronization + Expansion

P1

P2

x1P1

x2P2

c

d

C

faA (x1) D cC /

fbB (x2) D dD /

td

ijdˆ

X

• Hard scattering process well described by NLO pQCD calculation at high Q2

• Unique Signature at high energy: Hard scattering cross-section is large• Jet and Direct photon• Heavy Quark production: Charm(onium), Bottom(onium)

• Cross section in A+B collisions = TAB(b) p+p collisions• TAB(b): Overlap integral of nuclear profile functions Number of binary collision

s• =AB• Can be calculated by Geometrical description of Nucleus

view along beam axislooking from top

New probe to HEHIC: Hard scattering

In A+B collisions---In A+B collisions---TTABAB Scaling Scaling

Centrality 0% (Central)

Centrality 100% (peripheral)

Proportional to number of participated nucleons

A B

AB

Next-to-Leading Order (NLO)

Leading Order (LO)

Calibrating Hard scattering• High pT Direct photon in Au

+Au at sNN=200GeV• Electromagnetic probes brin

g out information on the stage it is emitted

• Direct access to hard scattering (pT>4GeV/c)

• Yellow bands show error due to three different cut-off scale of NLO pQCD scaled by number of binary collisions (Ncoll)

• NLO pQCD agrees very well with measurement• First measurement of hard s

cattered direct photon in heavy ion collisions! PHENIX, nucl-ex/0503003

Hard scattering cross-section in nucleus-nucleus collisions has been calibrated

X.-N., Wang, PRC 58 (1998)2321

Energy loss =Yield suppress

0 without energy loss

0 with energy loss

Yie

ld [

GeV

-1c]

pT [GeV/c]

coneRFragmentation:

hadron

parton

pz

p

Jet as a probe of dense mediumJet as a probe of dense medium• Parton may change its momentum in hot dense medium

• Energy loss through Gluon radiation, etc.• Reconstruction of Jet in Au+Au is impossible

• Trigger Leading particle of Jet• Angle correlation, Energy, momentum, etc. may reflect Jet kinematics

pT [GeV/c]

0-10% Centrality(Central)

High pT Identified hadron spectra(I)

• Produced in initial hard scattering process•Should scale with Ncoll if no additional process exists

• In peripheral Au+Au collisions, yield is consistent with p+p collisions scaled by Ncoll

• In Central Au+Au collisions, yield is significantly lower than p+p•Energy loss of hard scattered parton in hot and dense medium?

PHENIX, PRL91, 072301 (2003)

70-80% Centrality(peripheral)

pT [GeV/c]

sNN=200GeV

High pT Identified hadron spectra(II)• Nuclear Modification Factor: RAA

• Ratio of per-collision-yield to p+p• Hard scattering only: ratio is 1

• Peripheral Au+Au, Minimum bias d+Au: = 1• Central Au+Au: << 1

• Is suppression due to final state interaction?• Au+Au Direct photon: RAA= 1• Suppression is final state effe

ct• Energy loss of parton

in hot dense medium

• Medium expands in longitudinal direction as well?• Suppression at high rapidity regio

n• Answer is Yes!

pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

200

GeV

0

R AA /R

dA

d+Au Minimum bias

Au+Au Peripheral

Au+Au CentralBRAHMS, PRL91, 072305 (2003)

PHENIX, PRL91, 072301 (2003) PHENIX, PRL91, 072303 (2003)

away

near

Col

limat

edre

gion

away

Modification of away side Jet• Correlation of back-to-back jets t

hrough high pT hadrons

• Trigger leading high pT (4<pT<6) hadrons• Angle correlation of lower pT (2<pT<tr

ig) particles with triggered hadrons• Near side: In Same Cone of leading• Away side: In Cone of associated jet

• p+p and peripheral Au+Au:• Near side yield = Away side yield

• Central Au+Au: away side particles suppressed. • Energy loss of away side Jet• Near side jet produced almost at su

rface of medium Histogram: p+p, Black Points: Au+AuBlue Line: Mixed background

Au + Au central

Au + Au peripheral

Trigger particles sit at 0.

STAR PRL90, 082302 (2003)

Near(Trigger) Side Away Side

Even lower pT associated particles (1.0<pT<2.5)

Strong Modification of away-side Jet observed!Dawn of Jet tomography

(Folded into 0-)

hep-ph/0411315Casalderrey-Solana,Shuryak,Teaney

Wake effect or “sonic boom”

hep-ph/0411341Armesto,Salgado,Wiedemann

Correlations of Jets with flowing medium

Where is away side Jet ?Interpretation..

W. Holtzmann for PHENIX, WWND, 2005

Heavy Quark(onium)• Charm or bottom produced in hard scatt

ering process

• Energy loss of light quark is mostly due to gluon radiation (analogous to Bremsstrahlung)• How about heavier quarks? Collisional en

ergy loss? • Charmonium in hot dense medium will b

e:• Suppressed due to dissociation (debye s

creening)• Enhanced due to coalescence of c-cbar

D mesons

, ’,

Large Q value needed (>≈3GeV)

pQCD should work better!

Perturbative Vacuum

cc

Color Screening

cc

J/ (M=3.1GeV/c2)

•PHENIX•Single electron measurements in p+p, d+Au, Au+Au sNN = 130,200,62.4 GeV

•STAR•Direct D mesons hadronic decay channels in d+Au

•D0K•D±K•D*±D0

•Single electron measurements in p+p, d+Au

Phys. Rev. Lett. 88, 192303 (2002)

Single heavy quark measurement•Experimentally observe the decay products of Heavy Flavor particles (e.g. D-mesons)

•Hadronic decay channels DKD00

•Semi-leptonic decays De() Ke

Meson D±,D0

Mass 1869(1865) GeV

BR D0 --> K+- (3.85 ± 0.10) %

BR D --> e+ +X 17.2(6.7) %

BR D --> ++X 6.6 %

Single electron Result• Strong modification of the spectral sha

pe in Au+Au is observed at high pT

• Statistics insufficient to quantify centrality dependence

• Possibility of different energy loss mechanism?

T. Tabaru for PHENIX, ICPAQGP05, 2005

PHENIX PRELIMINARY

RAA of Integrated CS (2.5<pT<5.0 GeV/c).

AAAA

AB pp

dNR

T d

y2 x2 y2 x2

2cos2 vx

y

p

patan

dN/d=v0/(2)+v2cos(2) /+…

Where is suppressed Charm?

• Particles boosted by pressure gradients in collision area• Elliptic shape turns into

anisotropic flow• Positive flow(v2) = Collective motion with

expanding system

= Hint of equilibrium

• Energy loss of charm implies interaction of charm with the medium

• Charm participate in collective motion!

STAR, nucl-ex/0411007, Theory curves from:Greco, Ko, Rapp: Phys. Lett. B595 (2004) 202

Strong indication of “quark level” early equilibrium

R. L. Thews, M. Schroedter, J. Rafelski, Phys Rev C 63, 054905Plasma Coalescence Model

Binary Scaling

Stat.ModelAndronic et al nucl-th/0303036

Absorption (Nuclear + QGP) + final-state coalescence

Absorption (Nuclear + QGP)L. Grandchamp, R. Rapp, Nucl Phys A709, 415; Phys Lett B 523, 60

y = 1.0

y = 4.0

Phys.Rev.C69, 014901,2004 Not enough statistics to make definitive conclusions

Charmonium resultsFirst J/ ->ee measurement in heavy ion collisions!

J/->ee

Au+Au sNN=200GeV

Summary• Hard scattering (pQCD) as new probe for NpQCD QGP

• Cross section is significantly large at RHIC. Calculable by pQCD• Calibrated by Direct photon

• First measurement in high energy heavy ion collisions

• Jet modification• High pT particle yield (fragment of Jet) suppression in central Au+Au collisions

• Hot dense medium expanding both transverse and longitudinal direction• Away side jet is strongly modified

• Hint of Charm suppression and flow in Au+Au collisions• Needs more statistics to conclude

• High Statistics Run4 Au+Au data is now in analysis• 10 times statistics: ~ 1.5G events accumulated• Thermal radiation on top of pQCD photon -> Direct emission from QGP• 700 J/ ’s expected -> precise measurement of charmonium• Complemented by Run5 Cu+Cu data on system size dependence

• Hard scattering will be even more powerful probe at LHC

Future Outlook

RHIC Collaborations

STARSTAR