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

Is it Interesting?

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


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


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) of the 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)

Living in the cold QCD vacuum

It is generally believed in the fish population that there is an inherent resistance to motion and that they swim in a “vacuum”.

The vacuum – perceived to

be empty by the general

fish population

A clever (and crazy idea)

One clever young fish is enlightened. “The vacuum is complicated and full of water!” he says –” really there is no resistance to motion!”

“Phooey” say his friends, “we all know the vacuum is empty.”

How does he prove it? Answer – he builds a machine to boil the

water into steam – to “melt” the vacuum In steam his “friends” move freely.

OK OK – they die because They can’t breathe in air They are poached because of the heat

So maybe he boils only what’s in a small bottle as an experiment, and he calls this machine RICC (Relativistic Ice Cube Collider…

you get the point…

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 is it 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

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 TBjorken

dE

dyR

~6.5 fm

Remember, from the Lattice T = 150-200 MeV ~ 0.6-1.8 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 enegy Peripheral High y

Qs

S RHIC 130central

At RHIC, QS~1-2 GeVS(QS)~0.3 –0.4

Running of S

Why “Colored Glass Condensate?”

Colored? - Gluons are colored Condensate?

Gluons are interacting bosons and fill up the available states

Glass? - A glass is a material with A long time scale ~ Window glass induced by “frustration”

In Color Condensate we have “relativistic frustration”

Model Break Nucleus into Gluon Field, and Source

“Source” – quarks and gluons at high-x, Lorenz time dialated clock runs slow

Gluon field at low-x. Clock runs fast, but motion is governed by “source”. They are “frustrated”

HappyHard working

Gluons

Work Work Work Work

W….o…r… k … W . .

FrustratedGluons

“frustrated”Spin Glass

“happy”

quark

Time dialted quark

Calculations (post-diction) dN/dy for s, centrality, y, A energy in terms of

one variable: QS. Set QS at a single point

QS larger – more central, higher energy, mid-rapidity A constant C=CLCMult must be set

CL is gluon liberation coeefficient – probablility that a virtual gluon becomes “real” upon collision (can be calculated on the Lattice)

Cmult is the gluon multiplication coefficent from final state interations

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?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

beautiful

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 fails 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

Flow of Identified Particles

• Mass dependence at low pT is well described by hydro (lines, P. Huovinen)

Preliminary

What about Chemical and Thermal Equilibrium? (at freezout)

What have we measured? Global Features:

Chemical Equilibration

Model assuming Chemical Equilibration describes yields Pretty well s ~ 1

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

Particle Ratios

Central events

Is it themalized? Themal 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

Does anythingscale with binaries?

Single electrons from charm (a hard process?)

Fit to pythia charm scaled with BINARIES

Looks like it works!

(with apologies to the great work on charm production-note “dead cone effect”)

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!

Peripheral:

Consistent with Ncoll scaling

0-10% CENTRAL

Ncoll

=975±94

Central

Consistent with Ncoll scaling Central:


Scale up with Ncoll=12.3

70-80% PERIPHERAL

Ncoll

=12.3 ±4.0


PHENIX P

relim

inar

y

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 2 200 GeV)

RHIC – Run 1 (130 GeV)

0-10%

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

Nuclear Modification Factor

RHIC central -Suppressionperipheral – Ncoll 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%

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?

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 L dependence …

BH MFP

LPM

coh

01 dim expansion static

2

A

E ER

Phase transition from quench?

Calculate q 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

Theory Comparisons for RAA

Wang: X.N. Wang, Phys. Rev. C61, 064910 (2000).

dE/dx~constant, static source

GLV: Gyulassy, Levai, Vitev: P.Levai, Nuclear Physics A698 (2002) 631.

dE/dx~L (LPM) , static source

Vitev: GLV, Nucl. Phys. B 594, p. 371 (2001) + work in preparation.

Static source

Wang: dE/dx = 0

GLV: L/ = 4

GLV: L/ = 0

Wang: dE/dx =0.25 GeV/fmP

hen

ix P

relim

inary

More Theory Comparisons for RAA

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

RAu/ ~6 Assumes

independent scattering

dE/dx ~ 6%E What does

this mean????

dE/dx~0.03E GeV/fm

dE/dx~0.06E GeV/fm

dE/dx~0.10E GeV/fm

dE/dx~L (LPM)

dE/dx~0.3 GeV/fmConstant

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

Phenix Preliminary

0-10% CENTRAL

Ncoll

=975±94

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 !

p /

Central

Peripheral

Protons boosted to higher pt by flow?Pion quenched at high pt?

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?

Are there other ways to Look at this?

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 propogation

(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?

v2(pT) up to 12 GeV/c star

• Statistical errors only

• Finite v2 up to 12 GeV/c in mid-peripheral bin

v2(pt) proposed 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

Au+Au at sqrt(sNN)=200GeV

pT (GeV/c) pT (GeV/c)

v2

Negativespi-&K-,pbar

Positivespi+&K+,p

v2

v2 of identified hadronsr.p. ||=3~4min. bias

PHENIX Preliminary PHENIX Preliminary

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

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

pion proton

Azimuthal Asymmetries - Elliptic Flow

saturation of v2 observed hydrodynamic flow

increase with pT

Adler et al., nucl-ex/0206006

Azimuthal Asymmetries - Elliptic Flow saturation of v2 observed hydrodynamic flow

increase with pT

non-equilibrium contribution jets (unquenched) decrease with pT


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


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 Plenary Tuesday

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


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


t~0 Nuclei are Lorentz

contracted White – quarks Green – gluons

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


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(?) Themalization(?) Flow starts to develop

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100


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

Q#’s of vacuum Parton energy loss

~10 GeV/fm Chiral Symmetry?


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 Condesate

Develops? Mass develops?

Confinement sets in?

0.1 1

0.1

En

erg

y

Den

sity

(G

eV

/fm

3)

10Time (fm)

10

100


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 CGC? “tentatively” (dA, eA, theory) Does it thermalize? “tentatively” (theory)

Is there jet quenching? “probably” (dA) Do quarks thermalize? “I don’t know” Is the system in equilibrium at freezout “yes” Have we got it? (the QGP) … “maybe” Is there deconfinement?, chiral symmetry

restoration?….

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)

0-10% CENTRAL

Ncoll

=975±94

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 Size of system …

BH MFP

LPM

coh

01 dim expansion static

2

A

E ER

coh

coh

2

2

off single scatterer

BH type: if λ=mfp then

/ / /

LPM type: L Coherence length

now L

/ ~ / /

E

Where is the average kick from a single scatter

coh

LPMcr T

T

E fE

dE dx E Ef

E

dE dx E L fE E f E

Now p

p

2

ing

radiated gluon energy is < E : BH regime

radiated gluon energy is > E : LPM regime

What is E at RHIC? Use 1 GeV, and =1fm then we get 5 GeV

seems small for recent RHIC data

LPMcr

LPMcr

LPMcr Tp

(why?)

Or maybe ususal LPM calculations in static plasma don't work.

Parton Energy Loss

There are a variety of possibilities dE/dx ~ constant, static plasma (probably not physical) dE/dx ~ L

QCD calculations LPM type coherence dE/dx ~ E

From idependent scattering centers

Both Static and Expanding plasma considered

Partons are expected to lose energy via gluon radiation in traversing a quark-gluon plasma

Baier, Dokshitzer, Mueller, Schiff, hep-ph/9907267Gyulassy, Levai, Vitev, hep-pl/9907461Wang, nucl-th/9812021and many more…..

Theory Comparisons for RAA

Wang: X.N. Wang, Phys. Rev. C61, 064910 (2000).

dE/dx~constant, static source

GLV: Gyulassy, Levai, Vitev: P.Levai, Nuclear Physics A698 (2002) 631.

dE/dx~L (LPM) , static source

Vitev: GLV, Nucl. Phys. B 594, p. 371 (2001) + work in preparation.

Static source

Wang: dE/dx = 0

Vitev: dNgluon/dy = 900

GLV: L/ = 4

GLV: L/ = 0

Wang: dE/dx =0.25 GeV/fmP

hen

ix P

relim

inary

Richard Seto University of California, Riverside RHIC/STAR Workshop Bejing, PRC August 29-31, 2002

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Transcript of Richard Seto University of California, Riverside RHIC/STAR Workshop Bejing, PRC August 29-31, 2002