A Student’s Guide to A Student’s Guide to Hard Scattering at RHICHard Scattering at RHIC

Thomas K HemmickThomas K HemmickStony Brook UniversityStony Brook University

2

A Defining Moment for A Defining Moment for Me.Me. In 1988, Brookhaven National Lab held a school In 1988, Brookhaven National Lab held a school

for the students in the fledgling field of for the students in the fledgling field of Relativistic Heavy Ions.Relativistic Heavy Ions.

I was one of the attendees and am still grateful I was one of the attendees and am still grateful for this school nearly 20 years later for this school nearly 20 years later (I still have (I still have the Xeroxed notes)the Xeroxed notes)

One of my colleagues recently dug up the “class One of my colleagues recently dug up the “class photo”.photo”.

It is simply amazing that most of the people in It is simply amazing that most of the people in that photo are still in the field today…I credit that photo are still in the field today…I credit the school and its teachers:the school and its teachers:

BTW: The most popular teacher at that school…BTW: The most popular teacher at that school…Helmut Satz

3

Goals of this Goals of this PresentationPresentation Quark Matter is one of the most exciting, Quark Matter is one of the most exciting,

current, and results-filled conferences.current, and results-filled conferences. Necessarily, the talks use jargon heavily and Necessarily, the talks use jargon heavily and

assume knowledge of the history of the field.assume knowledge of the history of the field. I hope to give a self-contained (and I hope to give a self-contained (and

somewhat whirl-wind) tour over the somewhat whirl-wind) tour over the concepts, previous measurements, and concepts, previous measurements, and present issues in hard scattering present issues in hard scattering measurements.measurements.

My goal is to help you attain something of My goal is to help you attain something of the necessary background to fully enjoy this the necessary background to fully enjoy this conference.conference.

4

Nuclear Collision Nuclear Collision TerminologyTerminology

Centrality and Centrality and Reaction Plane Reaction Plane determined on an determined on an Event-by-Event basis.Event-by-Event basis.

NNpartpart= # of = # of ParticipantsParticipants 2 2 394 394

NNbinarybinary=# of Collisions=# of Collisions

Peripheral Collision Central CollisionSemi-Central Collision

100% Centrality 0%

Reaction Plane

Fourier decompose Fourier decompose azimuthal yield:azimuthal yield:

...2cos2cos21 21

3

vvdydpd

Nd

T

5

The ParadigmThe Paradigm We accelerate nuclei to high energies with the We accelerate nuclei to high energies with the

hope and intent of utilizing the beam energy to hope and intent of utilizing the beam energy to drive a phase transition to QGP.drive a phase transition to QGP.

The created system lasts for only The created system lasts for only ~10 fm/c~10 fm/c The collision must not only utilize the energy The collision must not only utilize the energy

effectively, but generate the signatures of the effectively, but generate the signatures of the new phase for us.new phase for us.

I will make an artificial distinction as follows:I will make an artificial distinction as follows: MediumMedium: The bulk of the particles; dominantly soft : The bulk of the particles; dominantly soft

production and possibly exhibiting some phase.production and possibly exhibiting some phase. ProbeProbe: Particles whose production is calculable, : Particles whose production is calculable,

measurable, and thermally incompatible with (distinct measurable, and thermally incompatible with (distinct from) the medium.from) the medium.

6

The Probes Gallery The Probes Gallery (Hard (Hard Scattering):Scattering):

Jet Suppression

charm/bottom dynamics

J/ &

direct photonsCONTROL

The importance of the control measurement(s) cannot be overstated!

7

Calibrating the Probe(s)Calibrating the Probe(s)

Measurement from Measurement from elementary collisions elementary collisions matches calculations.matches calculations.

Question: What goes Question: What goes into these calculations?into these calculations?

p+p->0 + X

Hard

Scattering

Thermally-shaped Soft Production

hep-ex/0305013 S.S. Adler et al.

“Well Calibrated”

8

Factorization Theorem:Factorization Theorem: Nucleon is a collection of Nucleon is a collection of

partons described by PDF.partons described by PDF. Pair-wise interactions of Pair-wise interactions of

partons at high Qpartons at high Q22 can can described by pQCD.described by pQCD.

Scattered partons Scattered partons materialize as jets via the materialize as jets via the fragmentation function.fragmentation function.

NOTE: Only the pQCD cross sections are fundamental. PDF and Fragmentation arebased upon measurement

Collins, Soper, Sterman, Nucl. Phys. B263 (1986) 37

9

Parton Distribution Parton Distribution FunctionsFunctions Parton Distribution Parton Distribution Functions are well Functions are well measured and measured and universal (at least universal (at least under the under the factorization factorization theorem).theorem).

Calculations Calculations (PYTHIA) use (PYTHIA) use theoretical form theoretical form guided by the data:guided by the data: CTEQ 5MCTEQ 5M others…others…

Parton distributions Parton distributions in nuclei are modified in nuclei are modified as compared to as compared to nucleons.nucleons.

F2

10

Fragmentation FunctionFragmentation Function

The fragmentation function, D(z) describes The fragmentation function, D(z) describes the process of by which a scattered parton the process of by which a scattered parton materializes as a jet of particles.materializes as a jet of particles.

A medium might be expected to modify A medium might be expected to modify D(z).D(z).

When the full jet is difficult to identify, z is When the full jet is difficult to identify, z is replaced by zreplaced by zTT referencing the leading or referencing the leading or “trigger” particle of the jet.“trigger” particle of the jet.

11

q/g jets as probe of hot q/g jets as probe of hot mediummedium

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

Jets from hard scattered quarks observed via fast leading particlesleading particles orazimuthal correlations between the leadingparticles

However, before they create jets, the scattered quarks However, before they create jets, the scattered quarks radiate energy (~ GeV/fm) in the colored mediumradiate energy (~ GeV/fm) in the colored medium

decreases their momentum (fewer high pT particles)“kills” jet partner on other side

Jet Quenching

12

Many Many measurements measure at measurements measure at high phigh pTT(!)(!)

13

RRAAAA Normalization Normalization

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

<Nbinary>/inelp+p

nucleon-nucleon cross section

1. Compare Au+Au to nucleon-nucleon cross sections2. Compare Au+Au central/peripheral

Nuclear Modification Factor:

If no “effects”: RAA < 1 in regime of soft physics RAA = 1 at high-pT where hard scattering dominates Suppression: RAA < 1 at high-pT

AA

AA

AA

14

pp

AuAubinaryAuAuAA Yield

NYieldR

/

Au-Au s = 200 GeV: high pT suppression!PRL91, 072301(2003)

Effect is real…seen by ALL 4 experiments…Final or Initial State Effect?

15

More than just a bunch of More than just a bunch of nucleonsnucleons

The parton distributionsThe parton distributionsin a nucleus differ fromin a nucleus differ fromthose of the nucleon.those of the nucleon.

Depletion at low xDepletion at low xis called shadowing andis called shadowing andexcess at intermediate xexcess at intermediate xis called anti-shadowing.is called anti-shadowing.

Shadowing calculations are theoretical Shadowing calculations are theoretical calculations “inspired” by experimental calculations “inspired” by experimental measurements (not fundamental).measurements (not fundamental).

gluons in Pb / gluons in p

x

An example of gluon shadowing prediction

AntiShadowing

Shadowing

16

probe rest frame

r/ggg

Color Glass CondensateColor Glass Condensate Gluon fusion reduces number of Gluon fusion reduces number of

scattering centers in initial state.scattering centers in initial state. Theoretically attractive; limits Theoretically attractive; limits

DGLAP evolution/restores DGLAP evolution/restores unitarityunitarity

17

Control ExperimentControl Experiment

Collisions of small with large nuclei quantify all Collisions of small with large nuclei quantify all coldcold nuclear nuclear effects.effects.

Small + Large distinguishes Small + Large distinguishes allall initial and final state effects. initial and final state effects.

Nucleus- nucleuscollision

Proton/deuteron nucleuscollision

Medium? No Medium!

18

NO suppression in d+Au!NO suppression in d+Au!

BRAHMS

Phobos

STAR

PHENIX

19

Centrality Centrality DependenceDependence

Dramatically different and opposite centrality Dramatically different and opposite centrality evolution of Au+Au experiment from d+Au control.evolution of Au+Au experiment from d+Au control.

Jet Suppression is clearly a final state effect. Jet Suppression is clearly a final state effect.

Au + Au Experiment d + Au Control Experiment

Preliminary DataFinal Data

20

Second Control Second Control ExperimentExperiment

The medium should be transparent to The medium should be transparent to photons.photons.

These thereby probe the initial rate of pQCD These thereby probe the initial rate of pQCD production and provide independent production and provide independent normalization of hard collision rates.normalization of hard collision rates.

q

21

Direct Photons in Au+AuDirect Photons in Au+AuPRL 94, 232301

Expectation for Ncoll scaling of

direct photons

holds for all centrality classes

00 suppression caused by medium created in Au+Au suppression caused by medium created in Au+Au collisionscollisions

22

So opaque, even a 20 GeV So opaque, even a 20 GeV 00 is is stoppedstopped..

Suppression is very strong (Suppression is very strong (RRAAAA=0.2!) and flat up to 20 GeV/c=0.2!) and flat up to 20 GeV/c Common suppression for Common suppression for 00 and and it is at partonic levelit is at partonic level > 15 GeV/fm> 15 GeV/fm33; dN; dNgg/dy > 1100/dy > 1100

23

Quantify the Energy Quantify the Energy LossLoss

Medium induced energy loss is the only currently known physical Medium induced energy loss is the only currently known physical mechanism that can consistently explain the high mechanism that can consistently explain the high ppTT suppression. suppression.

From GLV model, initial gluon density From GLV model, initial gluon density dndngg/dy/dy~1000~1000 is obtained. is obtained. This corresponds to an initial energy density This corresponds to an initial energy density ~15 GeV/fm~15 GeV/fm33..

RAA data vs GLV modelEmpirical energy loss from data

Fra

ctio

nal e

nerg

y lo

ss

24

How about a heavy probe: How about a heavy probe: Charm QuarkCharm Quark

Electon spectrum used Electon spectrum used to infer charm yield.to infer charm yield.

““Photonic” electrons Photonic” electrons measured with measured with convertor and convertor and subtracted. subtracted.

0.906 < < 1.042

dN/dy = A (Ncoll)

YieldYield scales with N scales with Nbinarybinary

Mass alone makes for Mass alone makes for valid pQCD regime.valid pQCD regime.

0eD K

0D K

0 0e eD D e e K K

0 0eD D e K K

0 0D D K K

c c

0DK+

-

0D

e+

D*0

25

Modification of CharmModification of Charm

Electrons from heavy quark decay Electrons from heavy quark decay have nearly same Rhave nearly same RAAAA as pions! as pions!

Electrons from heavy quark decay Electrons from heavy quark decay flow (“stopped in medium”)?flow (“stopped in medium”)?

But how do you stop a b-quark?But how do you stop a b-quark? Data imply small diffusion Data imply small diffusion

coefficient for charm.coefficient for charm.

M. Djordjevic, et. al. nucl-th/0507019

26

Jet TomographyJet Tomography Jets are produced as back-to-back pairs.Jets are produced as back-to-back pairs. If one jet escapes, is the other shadowed?If one jet escapes, is the other shadowed? Map the dynamics of Near-Side and Map the dynamics of Near-Side and

Away-Side jets.Away-Side jets. Vary the reaction plane vs. jet orientation.Vary the reaction plane vs. jet orientation. Study the composition of the jetsStudy the composition of the jets Reconstruct the WHOLE jetReconstruct the WHOLE jet

Find “suppressed” momentum & energy.Find “suppressed” momentum & energy.

Escaping Jet“Near Side”

Lost Jet“Far Side”

In-plane

Out-planeX-ray pictures areshadows of bones

Can Jet Absorption be Used to“Take an X-ray” of our Medium?

27

Back-to-back jetsBack-to-back jetsSTAR PRL 90, 082302 (2003)

Central Au + Au

Peripheral Au + Au2

2 2 2( ) ( ) (1 cos(2 ))D Au Au D p p B v

near side

away side

peripheral central

d + Aucontrol

0 3 (radians)

28

Back-to-Back wrt Reaction Back-to-Back wrt Reaction PlanePlane

STAR

STAR

Suppression stronger in Suppression stronger in the out-of-plane direction.the out-of-plane direction.

Indicates suppression Indicates suppression depends upon length of depends upon length of medium traversed.medium traversed.

In-plane

Out-plane

Dilemma: How to quantify “completely opaque”.• Get something to punch through.• Find the lost energy and momentum

29

Many sides of RMany sides of RAAAA

Can examine suppression at differing centrality Can examine suppression at differing centrality but same medium length (via emission angle)but same medium length (via emission angle)

nucl-ex/nucl-ex/06110070611007

30

Search for the Scaling Search for the Scaling VariableVariable

SHOCK-1! The data do not scale with SHOCK-1! The data do not scale with L, L, differing from the naïve energy loss picture.differing from the naïve energy loss picture.

SHOCK-2! The data do scale with L alone SHOCK-2! The data do scale with L alone and show no suppression for L<2 fmand show no suppression for L<2 fm

Au+Au collisions at 200GeV

LdLL)(

10-20%

50-60%

nucl-ex/nucl-ex/06110070611007

31

Away Jet cannot Away Jet cannot “Disappear”“Disappear”

Energy and momentum Energy and momentum conservation require that the “lost” conservation require that the “lost” jet must be found somewhere.jet must be found somewhere.

““Loss” was seen for partner Loss” was seen for partner momenta just below the trigger momenta just below the trigger particle…Search low in momentum particle…Search low in momentum for the remnants.for the remnants.

1 < pT (assoc) < 2.5 GeV/c

STAR

PHENIX

32

Correlation of soft ~1-2 GeV/c jet Correlation of soft ~1-2 GeV/c jet partnerspartners

PHENIX (nuclex/0507004)PHENIX (nuclex/0507004)

peripheral: normal jet pattern

“split” of away side jet!

Emergence of a Volcano Shape

33

Explanations for splittingExplanations for splitting Mach coneMach cone

Sonic (or displacement) shock wave Sonic (or displacement) shock wave propagating through strongly interacting propagating through strongly interacting medium.medium.

Cherenkov RadiationCherenkov Radiation Color charge equivalent to high velocity electric Color charge equivalent to high velocity electric

chgchg

Bent JetBent Jet Jet scatters through medium and is deflected Jet scatters through medium and is deflected

from back-to-backfrom back-to-back

ccs

em cos

nem1cos

34

Explaining Modification of Jet Topology

hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaneynucl-th/0406018 Stoeckerhep-ph/0503158 Muller,Ruppertnucl-th/0503028 A. K. ChaudhuriRenk & Ruppert Phys. Rev. C73 011901 (2006)

Wake Effect or “sonic boom”

nucl-th/0507063 Koch, Majumder, X.-N. Wang

Cherenkov Gluon Radiation

hep-ph/0411341 Armesto,Salgado,Wiedemann

Jets and Flow couple

nucl-th/0601012 Ma, Zhang, Ma, Zhang, Ma, Huang, Cai, Chen, He, Long, Shen, ShiHuang, Cai, Chen, He, Long, Shen, Shi

Transport Theory

nucl-th/0605054 nucl-th/0605054 Chiu & HwaChiu & Hwa

Mult. Scat.

35

Mach cones common in EM Mach cones common in EM plasmaplasma

Experimental Handle:3-particle correlations

36

Conical Flow vs Deflected Conical Flow vs Deflected JetsJets

Mediumaway

near

deflected jets

away

near

Medium

mach cone

Medium

away

near

di-jets

0

0

π

π

37

Three-Particle Three-Particle CorrelationsCorrelations

signal obtained by subtraction of dominant signal obtained by subtraction of dominant backgroundsbackgrounds flow components, jet-related two-particle correlationflow components, jet-related two-particle correlation

clear elongation (jet deflection)clear elongation (jet deflection) off-diagonal signal related to mach cone?off-diagonal signal related to mach cone?

_ _ =

Raw – Jet x Bkgd – Bkgd x Bkgd(Hard-Soft)(Soft-Soft incl. Flow)

Δ1

Au+Au Central 0-12% Triggered

Δ2

Some of both patterns

38

3-Particle Correlations in 3-Particle Correlations in PHENIXPHENIX

*

Hi pT

Assoc. pTs

Same Side

Away Side

(3 particles from di-jet) + (2 from dijet + 1 other)

PHENIX Preliminary

39

Correlation TopologiesCorrelation Topologies

*

Cone Jet

Deflected Jet

Normal Jet

Azimuthal Section:

(medium excitation)

(scattered jet axis)

(unmodified)

PH

EN

IX S

imul

atio

n

*

*

trip

les/

trig

ger

(A.U

.)

PHENIX Preliminary

Some of both patterns

Renk&Ruppert: Some of both OK

40

Near-Side Long-Range Near-Side Long-Range Correlation: the Ridge Correlation: the Ridge

Au+Au 20-30%

a

b

c c

ba) Near-side jet-like corrl.

+ ridge-like corrl. + v2 modulated bkg.

b) Ridge-like corrl. + v2 modulated bkg.

c) Away-side corrl.+ v2 modulated bkg.

41

Centrality Dependence of Centrality Dependence of the Ridgethe Ridge

yield of associated yield of associated particles can be particles can be separated into a separated into a jet-like yield and a jet-like yield and a ridge yieldridge yield jet-like yield jet-like yield

consistent in consistent in and and and independent and independent of centralityof centrality

ridge yield ridge yield increases with increases with centralitycentrality

STAR preliminary(J+R) method

(J) method

(J) method

yiel

d

,

)

Npart

3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV

42

““Ridge” Particle Ridge” Particle SpectrumSpectrum

jet-like spectra jet-like spectra harder than harder than inclusiveinclusive flatter for higher flatter for higher

trigger ptrigger pTT

ridge spectra ridge spectra similar to inclusivesimilar to inclusive slightly larger slopeslightly larger slope approximately approximately

independent of independent of trigger ptrigger pTT

STAR preliminary“jet”ridgecharged

dN /dpt pte p t /T

43

Anomalous CompositionAnomalous Composition

Large (anti)baryon to pion Large (anti)baryon to pion Bifurcation of RBifurcation of Rcpcp

One curve for mesonsOne curve for mesons One curve for baryons.One curve for baryons.

meson proves not mass meson proves not mass effect.effect.

Recombination:Recombination: Coalescing constituent quarks Coalescing constituent quarks

lifts baryon “disadvantage”.lifts baryon “disadvantage”.

44

Recombination ModelsRecombination Models Recombination models Recombination models

assume particles are assume particles are formed by the formed by the coalescence of coalescence of “constituent” quarks.“constituent” quarks.

Explain baryon excess Explain baryon excess by simple counting of by simple counting of valence quark content.valence quark content.

Baryon vs meson scaling Baryon vs meson scaling becomes natural consequencebecomes natural consequence

45

Some Lore and My Charge Some Lore and My Charge to Youto You When Rutherford lead the Cavendish Laboratory, When Rutherford lead the Cavendish Laboratory,

the scientists were thrown out and the doors the scientists were thrown out and the doors padlocked promptly at 6:00 PM.padlocked promptly at 6:00 PM. Charge to the scientists: Go Home and THINK!Charge to the scientists: Go Home and THINK!

When the Professor and two students shared the When the Professor and two students shared the three wishes from the Genie of the Lamp:three wishes from the Genie of the Lamp: Student 1: I wish to be the RICH and powerful ruler of a Student 1: I wish to be the RICH and powerful ruler of a

nation.nation. Student 2: I wish to live on a tropical isle with beautiful Student 2: I wish to live on a tropical isle with beautiful

people and no cares in the world.people and no cares in the world. Professor: I want them back in the lab by nightfall.Professor: I want them back in the lab by nightfall.

My charges to you:My charges to you: STAY OFF COMPUTER; STAY OFF COMPUTER;

Listen to talksListen to talks and THINKand THINK.. I want you back in the lab next week.I want you back in the lab next week.

46

Emergence of dijets w/ increasing Emergence of dijets w/ increasing ppTT(assoc)(assoc)

Narrow peak emerges cleanly.Narrow peak emerges cleanly. Open question: Punch-through or Open question: Punch-through or

Tangential?Tangential?

8 < pT(trig) < 15 GeV/c

pT(assoc) > 2 GeV/cpT(assoc) > 3 GeV/cpT(assoc) > 4 GeV/cpT(assoc) > 5 GeV/cpT(assoc) > 6 GeV/cpT(assoc) > 7 GeV/cpT(assoc) > 8 GeV/c

STAR QM2005

47

J/J/:Enigma wrapped in :Enigma wrapped in Mystery.Mystery.

3X Suppression3X Suppression(~same as CERN)(~same as CERN)

Models:Models: Dissolution and Dissolution and

recombination?recombination? Cronin Cronin

broadening?broadening? Feed-down?Feed-down?

dAuμμ

200 GeV

CuCuμμ

200 GeV

AuAuμμ

200 GeV

AuAuee

200 GeV

CuCuee

200 GeV

CuCuμμ

62 GeV

3X

c-cbar produced together.c-cbar produced together. Dissolve in plasma.Dissolve in plasma. Unlikely(?) to find appropriate mate.Unlikely(?) to find appropriate mate.

48

Enough of this Probe Enough of this Probe Business…Business…

What does the medium What does the medium itself have to say?itself have to say?

BAM

49

px

py

y

x

Pressure? “elliptic flow” Pressure? “elliptic flow” barometerbarometer

Origin: spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system spatial anisotropy momentum anisotropy

v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane

Almond shape overlap region in coordinate space

y2 x2 y2 x2

2cos2 v

...2cos2cos21 21

3

vvdydpd

Nd

T

x

zy

50

Adler et al., nucl-ex/0206006

Large vLarge v22 Hydrodynamic limit Hydrodynamic limit

exhausted at RHICexhausted at RHIC for for low plow pTT particles. particles.

Can microscopic Can microscopic models work as well?models work as well?

Flow is sensitive to Flow is sensitive to thermalization time thermalization time since expanding since expanding system loses spatial system loses spatial asymmetry over asymmetry over time.time.

Hydro models Hydro models require require thermalization in less thermalization in less than t=1 fm/cthan t=1 fm/c

51

52

What is needed to reproduce What is needed to reproduce magnitude of vmagnitude of v22??

Huge cross sections!!

53

Hints of Recombination Hints of Recombination in vin v22

Species dependence of vSpecies dependence of v22 well accounted well accounted for (except for (except ) by scaling v) by scaling v22 and p and pTT by n by n quarks.quarks.

200 GeV Au+AuSTAR preliminary

54

Theory I: Hydro-models Score Theory I: Hydro-models Score BoardBoard

The hydro-models which include both hadronic and QGP phases reproduce the The hydro-models which include both hadronic and QGP phases reproduce the qualitative features of the measured v2(qualitative features of the measured v2(ppTT) of pions, kaons, and protons.) of pions, kaons, and protons.

These hydro-models require an early thermalization (These hydro-models require an early thermalization (thermtherm<1fm/c) and high <1fm/c) and high initial energy density initial energy density > 10 GeV/fm > 10 GeV/fm33

Several of the hydro-models fail to reproduce the v2 and spectra Several of the hydro-models fail to reproduce the v2 and spectra simultaneously.simultaneously.

HBT source parameters are not reproduced by any hydrodynamic calculations.HBT source parameters are not reproduced by any hydrodynamic calculations.

55

Hot Result: Charm Flows!!Hot Result: Charm Flows!! Charm flows, but not as Charm flows, but not as

strong as light mesons.strong as light mesons. Drop of the flow Drop of the flow

strength at high pstrength at high pTT. Is . Is this due to b-quark this due to b-quark contributioncontribution??

The data favors the The data favors the model that charm quark model that charm quark itself flows at low pitself flows at low pTT..

Charm flow supports Charm flow supports high parton density and high parton density and strong coupling in the strong coupling in the matter. It is not a matter. It is not a weakly coupled gas.weakly coupled gas.

v2(D)=0.3 v2()

v2(D)=0.6 v2()

v2(D)=v2()

Greco,Ko,Rapp: PLB595(2004)202

56

The first promising result The first promising result of direct photon of direct photon measurement at low pmeasurement at low pTT from low-mass electron from low-mass electron pair analysis.pair analysis.

Are these thermal Are these thermal photons? The rate is above photons? The rate is above pQCD calculation. The pQCD calculation. The method can be used in method can be used in p+pp+p collisions.collisions.

If it is due to thermal If it is due to thermal radiation, the data can radiation, the data can provide the first direct provide the first direct measurement of the initial measurement of the initial temperature of the matter.temperature of the matter.

TT00maxmax ~ 500-600 MeV !? ~ 500-600 MeV !?

TT00aveave ~ 300-400 MeV !? ~ 300-400 MeV !?

Hot Result: Low momentum Hot Result: Low momentum photons shine.photons shine.

PHENIX preliminary

57

SummarySummary The matter formed at RHIC is a nearly “perfect” The matter formed at RHIC is a nearly “perfect”

(zero viscosity) fluid that is strongly coupled.(zero viscosity) fluid that is strongly coupled. Continued measurements of the fluid promise to Continued measurements of the fluid promise to

elucidate many of its most fundamental elucidate many of its most fundamental properties:properties: Viscosity.Viscosity. Opacity.Opacity. Number of degrees of freedom.Number of degrees of freedom.

RHIC program more wildly successful than best RHIC program more wildly successful than best hopes.hopes.

I hope I have sparked your interest and I I hope I have sparked your interest and I cordially invite you to learn more in the parallel cordially invite you to learn more in the parallel sessions on RHIC physics.sessions on RHIC physics.

58

Extra Slides…Extra Slides…

59

The Medium I: Initial Energy The Medium I: Initial Energy densitydensity Bjorken estimate of energy Bjorken estimate of energy

density:density:

dEdETT/dy(/dy() > dE) > dETT/dy/dyfinalfinal = 760 GeV= 760 GeV Three values of Three values of 00

min min = 2R/= 2R/fm/c (RHIC)fm/c (RHIC) fm/c fm/c

(SPS)(SPS) formform==ħħ/<m/<mTT>(>(formform) )

≤ ≤ ħħ/<m/<mTT>>final final = 0.35 fm/c = 0.35 fm/c thermtherm ≤ 1 fm/c (hydro-model)≤ 1 fm/c (hydro-model)

≤ ≤ 2 fm/c 2 fm/c (conservative)(conservative)

Conservative Conservative lower limitslower limits on on the energy density:the energy density:

(form) > 15 GeV/fm(form) > 15 GeV/fm33 (0.35 (0.35 fm/c)fm/c)(therm) > 2.8 GeV/fm(therm) > 2.8 GeV/fm33 (2.0 (2.0

fm/c)fm/c)

dy

dE

AT )(1

)( 0

00

These values are well in excess of These values are well in excess of ~1 GeV/fm~1 GeV/fm33 obtained in lattice QCD as the obtained in lattice QCD as the energy density needed to form a deconfined energy density needed to form a deconfined phase.phase.

60

Emergence of dijets with Emergence of dijets with increasing increasing ppTT(trig)(trig)

Au+Au, 0-5%

correlations (not background subtracted)correlations (not background subtracted)

Hint of narrow back-to-back peak for Hint of narrow back-to-back peak for higher phigher pTT(trig)(trig) Higher pHigher pTT(trig) reflects higher-Q(trig) reflects higher-Q22 hard hard

scatteringscattering

pT(trig)

pT(assoc) > 2 GeV/c

preliminary

STAR QM2005

61

Medium II: Medium II: ThermalizationThermalization

Hadron yields and spectra are consistent Hadron yields and spectra are consistent with thermal emission from a strongly with thermal emission from a strongly expanding source. expanding source.

The observed strangeness production is The observed strangeness production is consistent with complete chemical consistent with complete chemical equilibriumequilibrium

/K/p measurement in aBroad pt range

Stat. model fit:Tch~ 160MeV, s~1.0Strangeness saturation at RHIC?

stronger radial flow at RHIC?

Exp

ansi

on v

eloc

ity

Tkin ~ 100 MeV<vT/c> ~ 0.5

Chemical freezeout

Thermal freezeout

RHIC