richard seto university of california, riverside rhic/star workshop bejing, prc august 29-31, 2002

Richard SetoUniversity of California, Riverside

RHIC/STAR WorkshopBejing, PRC

August 29-31, 2002

WHY?

Where Does Mass come from?

Massive quarks in lite QCD? (u,d)

Chiral (R-L) Symmetry

Massless quarks! So Where does mass

come from?Massive quark?

Massless quarks

The Vacuum: Source of Mass

Start at high Temperature with massless quarks

Massless quarks

T>Tc

The Vacuum: Source of Mass

Start at high Temperature with massless quarks

Assume a background field = - goo of quarks and gluons

Similar to the higgs field for E-W theory

Couples to quarks(massless for now) and gluons

Potential term for has special Temperature Dependence

T>Tc

T<Tc

T~Tc

V()

LowTemperatureHigh

Massless quarks

T>Tc

The Vacuum: Source of Mass

T~Tc

As Temperature Cools past Tc

T>Tc

T<Tc

T~Tc

V()

LowTemperatureHigh

The Vacuum: Source of Mass As Temperature Cools

past Tc

Spontaneous symmetry breaking (I.e. chiral)

quark condensate at low Temperature

generates hadron masses

T>Tc

T<Tc

T~Tc

V()

LowTemperatureHighT~TcT~Tc

T<Tc

Condensate

Weird!

The idea that empty space should be full of complicated material is wilder than many crackpot theories, and more imaginative than most science fiction…

F. Wilczeck in Physics Today (April 1998)

The HOTHOT QCD vacuum

Can you create it? YES! AT RHIC RHI collision leaves

a region of excited qq and gluons – ie hot vacuum

What is the hot hot vacuum like? How hot is it? (Temperature) How sticky is it? (Energy Loss – aka Jet

quenching) How much energy can it store? (Latent

heat) What is its equation of state? What is (are) the phase transition(s) to a

cold vacuum like? 1st, 2nd order, cross over?

How does it generate mass? How/why does it confine? What interesting properties does it exhibit? …

Why it is timely

Theory + Experiment = Theory + Experiment = Understanding Understanding Theoretical Calculations Theoretical Calculations in regions

probed by experimentexperiment Experiments Experiments in regions calculable by

theorytheory New era of Precision (almost)

Precision CalculationsCalculations Precision Measurements Measurements

Precision Detectors Redundancy of measurements (4 detectors!) AA, pA (dA), pp, eA

Phases of Nuclear Matter

TWO phase transitions! The deconfinement

transition - particles are roam freely over large volume

The chiral transition - masses change

All indications are that these two are at or are very nearly at the same TC

T

Tc

Lattice Calculations

T

Tc

(F. Karsch, hep-lat/9909006)

/T4

T/Tc

Lattice Results Tc(Nf=2)=1738 MeVTc(Nf=3)=1548 MeV

0.5 4.5 15 35 GeV/fm375

• Transition – Sharp Crossover at RHIC

• That’s OK – 1st order for all practical purposes

Lattice Calculations:Tc = 170 15% MeV critical ~ 0.6 GeV/fm3

Critical point

1st order

Sharp Crossover

Stages of the Collision

Various stages Must be described using different physics

Hard Soft

Detectors see sum of all phenomena Importance of hard probes Keep an open mind –no single idea (or theorist) can

explain everything

Data

4 detectors STAR – Large acceptance PHENIX – photons, leptons PHOBOS – small, low-pt BRAHMS – small, high y

Runs 130 GeV run 200 GeV run – results from recent QM

Is it like the Vacuum?

Quantum Numbers of the Vacuum?

Baryon number = zero?

0.8pp

~YES

AGS

SPS

√s [GeV]

PHENIX preliminary

STAR prelim 1.0

0.1

p/p ratio

~0.002

~0.05

STAR 200prelim

Note: Thermal fitB~30 MeV

Worlds dependence

How Hot is it? Is it Hot enough?

dET/dy ~ The Initial Energy Density

PHENIX: Central 200 GeV Au Au

T

=0

dE=573±2GeV

d

Thermalization tim

e ?

High Initial energy High Initial energy density-density-Its “HOT “enough!Its “HOT “enough!

Bj~ 5.2 GeV/fm3

Bj~ 26.0 GeV/fm3

Latticec

R2

c

20

1 1~T

Bjorken

dE E

dy VR

~6.5 fm

Remember, from the Lattice T = 170 MeV ~ 0.6 GeV/fm3

You said theory was getting better. Can you make reliable calculations of the initial conditions?

QCD - Notoriously hard to calculate Regime where QCD simplifies:

High Gluon Densities at low-x gluons ~ x- ,i.e. there are more of

them as you go to lower x They begin to overlap Gluons saturate

Classical Approx (McLerran, Venogopolan etc)

Robust calculations in QCD using “renormalization group” methods

Depends on a single scale

The Colored Glass CondensateA layman’s view

xG(x)

x

High x

low x

QS2=(1/R2)(dNgluon/dy) ~ 2-D gluon density

At RHIC, QS~1-2 GeV

The Approximation

The Approx Non-perturbative (high

density) Small coupling

Requires S(QS) to be “small”

Expected to fail for QS small

Low energy Peripheral High y

Qs

S RHIC 130central

At RHIC, QS~1-2 GeVS(QS)~0.3 –0.4

Running of S

Calculations dN/dy for s, centrality, y, A energy in terms of

one variable: QS. Set QS at a single point

Predict dN/dy for all other s, centrality, y QS larger – more central, higher energy, mid-rapidity

A constant C=CLCMult must be set CL is gluon liberation coefficient – probability that a virtual

gluon becomes “real” upon collision (can be calculated on the Lattice)

Cmult is the gluon multiplication coefficient from final state interactions

We would like this to be >1, otherwise thermalization produces no new particles

One to one correspondence between gluons and final state particles (I.e. entropy conserved)

Does it work? (post-diction)Saturation models can predict the scaling with centrality and rapidity!

Kharzeev & Levin, nucl-th/0108006Schaffner-Bielich et al, nucl-th/0108048

Np

dN

ch/d

/(0

.5N

p)

Kharzeev/Levin

energy density

~18GeV/fm3

Does this explain why dN/dy is less

than we might have thought?

QS depends on Npart,

S, y If S did not run,

there would be no dependence!

Dependence on NpartS, y

/ Constant0.5* ( )

gluon

part sS

dN dy

N Q

Prediction at 200 GeV

Not bad!

0-6%

15-25%

35-45%

Kharzeev/Levin

Prediction at 22 GeV Do we expect it to work?

At low energy QS becomes small S large

Expected to fail first for Peripheral High y

Np100

1

0200 400300

20-6%

15-25%

35-45%

Fails (worst for peripheral, high y)

All data PHOBOS Preliminary

0-6%

35-45%

15-25%

Is it thermalized? When?… it better be early, before hadronization,

if you are interested in a QGP…

Azimuthal anisotropy: v2 “Elliptic flow”

Late equilibration i.e. free streaming in early stages causes almond shape to become spherical

Strong elliptic flow Early thermalization

2 2

2 2 2cos 2x y

x y

p pv

p p

Momentum space: final asymmetry

multiple collisions (pressure)

py

px

x

y

Coordinate space: initial asymmetry

Elliptic Flow

Hydrodynamical model (Kolb et al)Good pt<2, more centralRapid thermalization

0 ~ 0.6 fm/c~20 GeV/fm3

(possibly later if some comes from CGC?)

RHIC: Very strong elliptic flow

What about Chemical and Thermal Equilibrium? (at freezout)

Thermal model fit-Chemical Freezout

Model assuming Chemical Equilibration describes yields Pretty well s ~ 1

From yields, 130 GeVTch freezeout=177 MeVBaryon=36 MeV

Particle Ratios

Central events

Thermal Model fit - Kinetic Freezout

Tthermal freezout ~ 130 GEV ~AGS/SPS

radial increases to ~ 0.5

From inverse slopes

As at SPS Strange particlesFreeze out earlierOmegas freeze-out differently? Explosive radial expansion

high pressure

130 GeV

K*

STAR 200

You’ve talked about the initial state, and the final state. What about the stuff in the Middle? Do you have a QGP?

ColorlessHadrons

ColoredQGP

Beams of colored quarks

Hard Probes, aka Jet quenching

Deep Inelastic Scattering of the QGP?

“hard” probes Formed in initial

collision penetrating sensitive to state

dE/dx by strong interaction

jet quenching

Jets by Jets by leading particles Look forLook for a a

suppression of high suppression of high pT hadron production.pT hadron production.

Scaling from pp to AA

Low pT

•Thermal •Hydro(Flow)•Exponential in MT

Npart

Scaling

High pT

•Jetlike•Jet frag (No flow)•Pwr law in pT

Nbin Scaling

Transition ~ 2 –4 GeV?

Nbinary at high pT

Npart at low pT

pp effects Intrinsic kT

pp to pA effects “Cronin effect”, initial state quark

scatteringi.e. pT broadening

Enhances higher pT

Nuclear shadowing Gluon shadowing

is not measured large role at RHIC

Models – scaling pp to AA

Measure pA at RHIC!

pp 0 spectrum

Peripheral:

Consistent with Nbin scaling

0-10% CENTRAL

Nbin

=975±94

Consistent with Nbin scaling?

NO Central:

Consistent with Nbin scaling

Scale up with Nbin=12.3

70-80% PERIPHERAL

Nbin

=12.3 ±4.0

Consistent with Nbin scaling

PHENIX P

relim

inar

y

NO!

Scaled pp

AuAu

RHIC – Run 2 200 GeV) 5!

Nuclear Modification Factor

Effect of nuclear medium on yieldsRun 2 Data Shows a manySigma Effect!

SPS – shows Cronin Effect

RHIC – Run 1 (130 GeV)

0-10%

(dE/dx)initial~7 GeV/fm15x Cold matter (Hermes)

PHENIX Preliminary

binary scaling

0-10%

70-80%

central binary centralAA T

pp

Yield NR (p )

Yield

/

RHIC central -Suppressionperipheral – Nbin scaling

PHENIX P

relim

inar

y

Centrality Dependence of RAA

Smoothly varies with centrality

PHENIX P

relim

inar

y

Smoothly varies with centrality

Dependence changes with pt?peripheral central

How does Jet energy loss depend on energy, path length etc?

What can we learn? Types of energy loss

Constant (probably not physical)

QCD motivated Bethe-Heitler (BH) type

dE/dx~E LPM type

dE/dx~ L ~E gluon coherence>MFP or Egluon> Ecr~pT,gluon

2 MFP 5 GeV at RHIC (?)

Static and Expanding plasma considered

Can learn about Energy loss mechanism Density of gluons ~ gluon

L dependence …

BH MFP

LPM

coh

01 expansion static

2D

A

E ER

Phase transition from quench?

Calculate qhat from QGP, pion gas

Jet quenching sensitive to energy

density NOT phase

transition? But this calculation

does not have confinement, chiral symmetry restoration…

2ˆSE qL

Massless pion gas

Ideal QGP

Nuclear Matter

Phase Transition?

Energy Density (GeV/fm3)En

erg

y L

oss

Coeffi

cien

t (G

eV

2/f

m)

BDMS

Vitev: GLV, nucl-th/0204019, PRC 65 (2002) 041902Comparing to 130 GeV theoryLPM type, Static Source

Theory Comparisons for RAA – GLV

Theory Comparisons for RAA –BH type

Compare to B-H type loss (dE/dx~E)

Static source RAu/ ~6

Assumes independent scattering

dE/dx ~ 6%E

dE/dx~0.03E GeV/fm (BH)

dE/dx~0.06E GeV/fm (BH)

dE/dx~0.10E GeV/fm (BH)

dE/dx~L (LPM)

dE/dx~0.3 GeV/fmConstant

Jeon, Jalilian-Marian, Sarcevic nucl-th/0208012

Phenix Preliminary

What about charged particles?

Charged particles: Central to Peripheral Ratio

peripheralbinaryperipheral

centralbinarycentral

NYield

NYield

//

Suppression seen in 3 independent measurements

Difference in 0/charged h ratio particle composition

(A variation on RAA)

Single Particle Spectra (0-5 %) Jet Fragmentation?

PHENIX Preliminary

Au+Au at sqrt(sNN) =200GeV

proton/antiproton contribution above pT > 2 GeV dominates charged spectra !

Particle Composition at high pT

0/(h++h-)/2 ratio ~ 0.5 up to 9 GeV/c do protons

continue to make up a large fraction of the charged hadron yield?How far in pt is hydrodynamics (flow) applicable?Is some other physics responsible?

Are there other ways to Look at “jet quenching”?

v2 “Elliptic flow” from jets energy loss?

2 2

2 2 2cos 2x y

x y

p pv

p p

Momentum space: final asymmetry

multiple collisions (pressure)

py

px

x

y

Coordinate space: initial asymmetry

distance of fast parton propagation

(energy loss)

Jet 1

Jet 2

V2 Non-flow component?

Methods of extracting v2

Momentum vs Event plane

Correlations 4th order cumulant

Sensitive only to flow

~20% of v2 from non-flow components Jets?

Azimuthal Asymmetries - Elliptic Flow

saturation of v2 observed hydrodynamic flow

increase with pT

non-equilibrium contribution jets (unquenched) decrease with pT

asymmetric energy loss

increase of v2 saturation from interplay models necessary

to disentangle effects

Adler et al., nucl-ex/0206006

Can you look at Di-jets?

2-Jet-Events in pp in the STAR TPC

p+p dijet from 200 GeV run

D. Hardtke, STAR

Two-particle azimuthal correlations

Identify jets on a statistical basis

Trigger particle with pT>pT(trigger)

associate particles with pT>pT(associated)

C2 is probability to find another particle at (,)

pT(associated)>2 GeV/c pT(trigger): 4-6 GeV/c,

3-4 GeV/c, 6-8 GeV/c ||<0.7 ||<1.4

2

1 1( , ) ( , )

Trig

C NN Eff

Jet

Away side Jet

Trigger jet shows little centrality dependence

Away side-Jet Suppression

Away side-jet strong suppression

with centrality jet quenching?

?

trigger-jet

Away side -jet

Centrality dependence similar to quenching of neutral pion spectrum!

Stages of the CollisionWhat can we say?

0.1 1

0.1Energ

y

Densi

ty

(GeV

/fm

3)

10Time (fm)

10

100

Stages of the Collision

Simulation and model byK. Geiger, …. From L. McLerran

modified by R.Seto

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100

Stages of the Collision

t~0 Nuclei are Lorenz

contracted White – quarks Green – gluons

large number of (low x) gluons in the center of the nuclei

Stages of the Collision

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100

Initial State t~0.1-0.6 fm ~20-30 GeV/fm3

Hard processes – PQCD Soft Processes – CGC(?) Early Thermalization(?) Flow (elliptic) starts to

develop

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100

Stages of the Collision

QGP??? t~0.6-2.0 fm ~2-3 GeV/fm3

Q#’s of vacuum Parton energy loss

~10 GeV/fm Chiral Symmetry?

Stages of the Collision

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100

Mixed Phase? t~2-5 fm Phase Transition? Latent Heat? Chiral Condensate

Develops? Mass develops?

Confinement sets in?

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100

Stages of the Collision

Freezeout Chemical

T~175 MeV B~30 MeV S~1

Thermal T~130 MeV ~0.5

Finally – What do we know? Have we created a very high energy density – greater than

needed for a QGP “yes” Does it have the Quantum numbers of the vacuum? “yes” Initially what is it? “gluons-Very strongly Interacting

Init cond-Colored Glass Condensate? “tentatively” (dA, eA, theory)

Does it thermalize? “tentatively” (theory needed?) When? “ tentatively early t=0.6 fm/c”

Is there jet quenching? “probably(almost certainly)” (dA needed)

Do quarks thermalize? “probably – final hadrons seem thermalized”

Is the system in equilibrium at freezout “yes” Have we got it? (the QGP) … “maybe” Is there deconfinement?, chiral symmetry restoration?….WE HAVE COME A LONG WAYS,

BUT THERE IS STILL A LOT OF WORK TO DO!

pT (GeV/c)

v2

Negativespi-&K-,pbar

PHENIX Preliminary

hydro model including the1st order phase transition with Tf=120MeV (*)

pion proton

v2

Au+Au at sqrt(sNN)=200GeVr.p. ||=3~4min. bias

(*) P.Huovinen, P.F.Kolb, U.W.Heinz, P.V.Ruuskanen and S.A.Voloshin, Phys. Lett. B503, 58 (2001)

v2(pt) of identified hadronsproposed scenario: flavor dependence

Baryon production by a non-perturbative mechanism (junctions or hydro)

M. Gyulassy, I. Vitev, X.N. Wang and P. Huovinen, Phys. Lett. B 526 (2002) 301-308

pions

protons

RHIC – Run 2 200 GeV) 5!

Nuclear Modification Factor

central binary centralAA T

pp

Yield NR (p )

Yield

/

Effect of nuclear medium on yieldsRun 2 Data Shows a manySigma Effect!

SPS – shows Cronin Effect

RHIC – Run 1 (130 GeV)

0-10%

(dE/dx)initial~7 GeV/fm15x Cold matter (Hermes)

Nuclear Modification Factor

RHIC central -Suppressionperipheral – Nbin scaling

PHENIX Preliminary

binary scaling

central binary centralAA T

pp

Yield NR (p )

Yield

/

Effect of nuclear medium on yields• Comparison of peripheral to central

0-10%

70-80%

Hidden slides

Connections…

“The experimental method to alter the properties of the vacuum may be called vacuum engineering. An effective way may well be to to use Relativistic Heavy Ions… If indeed we are able to alter the vacuum, then because the vacuum is ever present and everywhere, our microscopic world of elementary particles would become inextricably connected to the macroscopic world of the cosmos.”

T. D. Lee in Particle Physics and Introduction to Field Theory

(1981)