Search for quark-gluon plasma at RHIC

Vladislav Pantuev, University at Stony Brook

And in PHENIX collaboration

• RHIC – Relativistic Heavy Ion Collider - is addressing 2 fundamental physics questions

what was the universe 10-6 sec later?

how does the

nucleon get its spin?

Karsch, Redlich, Tawfik, Eur.Phys.J.C29:549-556,2003

In the beginning…

Thermal QCD ”QGP” (Lattice)

/T4

“In 1972 the early universe seemed hopelessly opaque…conditions of ultrahigh temperatures…produce a theoretically intractable mess. But asymptotic freedom renders ultrahigh temperatures friendly…” Frank Wilczek, Nobel Lecture (RMP 05)

“Before [QCD] we could not go back further than 200,000 years after the Big Bang. Today…since QCD simplifies at high energy, we can extrapolate to very early times when nucleons melted…to form a quark-gluon plasma.” David Gross, Nobel Lecture (RMP 05)

170 MeV

Th

erm

al

Ha

dro

n G

as

Phase Diagram

Measurement of transverse energy: Initial energy density significantly above Trans

Transition: T ~ 170 MeV

~ 1.0 GeV/fm3

RHIC • Circumference: 3.83

km• Two rings• Maximum energy

(center of mass)

– Au+Au: up to 200 GeV– p+p: up to 500 GeV

• First collisions 2000• Run 7 about to start

p+p d+Au Au+Au Cu+Cu

200 GeV

130 GeV

62.4 GeV

22.4 GeV

Reference sQGP ? Comp.

RHIC after 6 years of running

0 Current run (?)Each Run about ½ year, last Run6 was on $12 mln. donation

Side-to-beam view

Along-the-beam view

Hot Zone

Au+Au central collision at √sNN = 200 GeV

STAR Experiment at RHIC

Centrality is determined by Multiplicity Detectors

JET Tomography

Nuclear Modification Factor RAA

• Hard processes

– Scale with Ncoll

– reason: • Small cross section• superposition

• Nuclear Modification-

Factor RAA

evt 2AB AB T

AB 2AB pp T

1 N d N /dydpR

T d /dydp

• In the absence of nuclear effects: RAA=1 at high pT

no effect

= (A+A)/[Ncoll*(p+p)]

RAA : Centrality Dependence

Run4 Data

Au+Au 200 GeV

Run4 0 Data

RAA in AuAu at 200 GeV

Photons are not suppressed

and even at high pT suppressedSuppression is flat at high pT

RAA – Reaction systems

• Geometrical model with “corona” effect

– More jets from surface – Correlated with ellipticity

Au+Au30-40%

Npart

= 114

Cu+Cu0-10%

Npart

= 98.2

Baryons vs

MesonsMarkedly different

suppression patterns! below

~6 GeV/c.

Large change in M/B ratio.

Above 5-6 GeV/c – no difference

Initial state effects? Control measurement in d+Au

No strong initial-state effects

Conclusions 1

• Strong jet suppression at high pt

• Factor 5 suppression in most central events, does not depend on pt

• Baryons and mesons have different behavior at intermediate pt. Baryon excess?

• Direct photons follow N-collision scaling, no medium effect

• Initial state effects, like low-x gluon saturation, can not explain the observed suppression

Elliptic Flow

Flow features in experimental observations:

xz

y

1

2

3

3

cos212

1

nn

TT

nvdydpp

Nd

pd

NdE

Reaction Plane

Why elliptic flow? - Different pressure gradients in plane and out of reaction plane. Sensitive to early evolution

Flow – unexpected feature of produced medium

PRC (72), 014904 (2005) Mass ordering at low pT:ideal hydro with early thermalization

Above pT ~2 GeV/c two groups of hadrons:

, K0s, K,

p, Λ, ,

Gas of weakly interacting particles can not produce such flow.

Prediction was: no/small flow!

P.S. More than 90% of produced particles are at pt < 2 GeV/c. The whole bulk of matter flows!

Flow for Light Hadrons

TT KEp

v2 scales with thetransverse kineticenergy! As hydro tells us.

Flow: Light Quarks → Strange

baryonsbaryons

mesonsmesons

Quark content determines v2

Simplistic hadronization model :v2q = v2h(pT/n)/n

mesons vs baryons flow scales with nq

Flow: meson with mass close to proton mass

System is in thermal and chemical equilibrium!

The (s)Quark-Gluon-Plasma ?

APS: The Top Physics Stories for 2005

Free gas of massless quarks and gluons ?No, strongly coupled!

Liquid!

Gaseous?

The (s)Quark-Gluon-Plasma ?

APS: The Top Physics Stories for 2005

Free gas of massless quarks and gluons ?No, strongly coupled!

Liquid!

Gaseous?

Conclusions 2

• Strong collective effects in radial and elliptic flow• Constituent quark scaling for v2 suggests

partonic phase• V2 is close to ideal hydro limit (low viscosity)• Wording sQGP – strongly interacting Quark-

Gluon Plasma and even “Perfect fluid” – become popular

• Standard parton energy loss models can not explain large v2 at high pt (I did not discuss this)

Jets in Medium

Di-jets: Away-Side Disappearance

• consistent with surface emission

• more intuitive hint for “jet” suppression, but quantitatively much more difficult

hadron --- hadron correlations

Trigger: 4-6 GeV/c

Partner: 2-PT

STAR PRL 91, 072304 (2003)

PHENIX PRL 97,052301,2006

STAR Preliminary

Away-Side BroadeningDecreasing Partner pT

hadron --- hadron correlations

Trigger: 4-6 GeV/c

Partner: 1-2.5 GeV/c

h± --- h±

C: VariousT: 2.5 - 4

P: 1 - 2.5

Trigger direction

Pair opening angle

Suggestive of…Cherenkov cone? Unfaivor. Mach cones?

Away-Side Emergence

8 < pT(trig) < 15 GeV/c

Adams et al., STAR nucl-ex/0604018

Increasing Partner pT

Fix PT Trig

Raise PT

Part

Away side jet remains, but suppressed

Conclusions 3

• Single jet shape does not change

• At pt < 2.5 GeV/c new collective effect for away side jet – Mach Cone angular structure

• If both jets are at high pt, there is factor 4-5 suppression for away side jet

Heavy Quarks

~factor 2

D0

PHENIX Non-Photonic Electrons –

From Charm and Bottom quarks

Experiment/Theory Ratio: 1.72 +/-0.02 (stat) +/- 0.19 (sys)(0.3 < pT < 9.0 GeV/c)

hep-ex/0609010

hep-ex/0609010 (accepted by Phys. Rev. Lett.)

CD

F,

PR

L 91

, 24

1804

(2

003)

Theoretical Uncertainty Band

Heavy Flavor in Au+Au

No suppression at low pT

Suppression observed for pT>3.0 GeV/c, smaller than for light quarks.

PHENIX nucl-ex/0611018(submitted to Phys. Rev. Lett.)

Heavy Quarks Energy Loss and Flow

Radiative energy loss only fails to reproduce v2

HF.

Heavy quark transport model has reasonable agreement with both RAA and v2

HF.

Small relaxation time or diffusion coefficient DHQ

inferred for charm.

nucl-ex/0611018(submitted to Phys. Rev. Lett.)

“Canonical” energy loss models fail to reproduce data

Debye screening predicted to destroy J/ψ’s in a QGP with different states “melting” at different temperatures due to different binding energies.

AuAu J/ψ’s - Quark Gluon Plasma signature?

Color Screening

cc

NA50 anomalous suppression

J/ Suppression at SPS and RHIC

Suppression patterns are remarkably similar at SPS and RHIC!

Cold matter suppression larger at SPS, hot matter suppression larger at RHIC, balance?

Recombination cancels additional suppression at RHIC?

How did we get so “lucky”?

NA50 at SPS (0<y<1)PHENIX at RHIC (|y|<0.35) eePHENIX at RHIC (1.2<|y|<2.2)

New: Good reference: J/ in p+pImproved Run-5 pp reference data

hep-ex/0611020, PHENIX(submitted to Phys. Rev. Lett.)

J/ RAA in Au+Au Collisions

Suppression close to light hadrons

Less suppression at central rapidity

Suppression is not solely due to local particle density.

Au+Au collisions at 200GeV

Rapidity Dependence

Rapidity measured over wide kinematic range for a variety of centralities and systems.

Significant constraint for recombination models.

Momentum spectrum Au+Au 200 GeV

Recent lattice calculations suggest J/ψ not screened after all.Suppression only via feed-down from screened C & ’, which give ~40% of

Quarkonium dissociation temperatures – Digal, Karsch, Satz

Regeneration models give enhancement that compensates for screening?

Summary – J/ SuppressionA puzzle of two (or more) ingredients

0 mb

3 mb

Low x2 ~ 0.003(shadowing region)

CNM needs better data constraint

Experimental homework

nucl-ex/0611020

Regeneration compensates for strong destruction?

Theoretical homework

0 = 1 fm/cused here

SPS overall syst (guess) ~17%

PHENIX overall syst ~12% & ~7%

difficult to compare RHIC to SPS suppression – but may be similar

Sequential screening and forward-y gluon saturation?

nucl-ex/0611020

Forward/mid rapidity suppression ratio saturates @~0.6

Most recent hits

Study near-side yields

Study away-side correlated yields and shapes

Components near-side jet peak

near-side ridge

v2 modulated background

STAR coll. - Jet sits on the Ridge?

3<pt,trigger<4 GeV

pt,assoc.>2 GeVAu+Au 0-10%

preliminary

d+Au, 40-100% Au+Au, 0-5%

3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

Direct RAA at 200 GeV, Run4

Direct RAA with measured

p+p reference data

η π0

Pion absorption versus angle w.r.t. reaction plane – other way to control thickness of the medium

Centrality 40-50%

At fixed centrality change parton path length by varying and keeping the same :

•Initial conditions

• Longitudinal and transverse expansion

12

The results:

3 < pT < 5 GeV/c 5 < pT < 8 GeV/c

-RAA in plane and out of plane changes by factor ~2

- For peripheral bins no suppression in plane, while a factor ~2 out of plane

PHENIX Run2, nucl-ex/0611007, submitted PRC

13

We vary path length by centrality and angle , both results should agree

Colors represent different centralities

RAA is universal function of Lnot L

RAA~1 and no energy loss for L < 2 fm

Variable L, distance from the

center of interaction region to the edge

60-70%

10-20%

All models are in big trouble!

Flow contribution up to 8 GeV/c?

Cronin effect?

Something else?

14

Why no absorption? Alternative explanation: Time matters!

Let jets fly in ANY direction:

Ncoll distribution in transverse plane, Glauber + Woods-Saxon

Stop jet after some time T.

T =2.3 fm/c to fit peripheral data

see V.P. hep-ph/0506095

16

The result:

Results of calculation

Describes inclusive RAA and dependence

Describes v2 at high

pT,

Simple explanation of lack of absorption in a layer < 2 fm,

Some other features

17

From V.P. hep-ph/0506095

Final conclusions:

• New form of matter is produced at RHIC, sQGP• Its properties are different from naïve

expectations of weakly interacting partons• Medium is more close to liquid in its properties• There are many parton energy loss models, but

no good theory• Big hopes on new approach: AdS/CFT

correspondence and new methods to calculate strongly interacting matter

• New impact from “conventional” plasma theory, from “dusty plasmas”

Hot questions that RHIC will answer (soon)

– fast thermalization mechanism?– how low is the viscosity of the liquid?– response of plasma to deposited energy?– what is the color screening length? – nature of phase transition? critical point?– equation of state of hot QCD matter?

Russian participation at PHENIX

• IHEP, Protvino

• JINR, Dubna

• Kurchatov Institute, Moscow

• PNPI, Gatchina

• Polytechnic University, St. Petersburg

Around 50 participants (from ~400 at PHENIX total)

Backup

Calculate elipticity parameter at high pt v2 as

jet surviving probability

in and out of plane

Data are for high pt pi0s, PHENIX,

blue cicles – 4.59 GeV/c,

green squares – 5-7 GeV/c, preliminary

hep-ph/0506095.No hydro/collective flow!

J/ <pT2>

New p+p reference (|y|in [1.2,2.2]):

Evaluated for pT<5 GeV/c where all systems have data.

New p+p reference (|y|<0.35):

222 /cGeV 14.006.037.3 Tp

222 /cGeV 15.018.007.4 Tp

PHENIX e+e-

PHENIX +-