Empirical Constraints on Hadronization of Bulk Matter

at RHIC

International Workshop on QCD and Experiments at RHIC

August 9-14, 2004

Beijing, P.R. China

Huan Zhong Huang

University of California at Los Angeles

Outline

1) Formation of Dense Matter in Nucleus-Nucleus Collisions at RHIC

2) Conventional Fragmentation Scheme Fails

3) Nuclear Modification Factors RAA/RCP

and Azimuthal Angular Anisotropy v2

4) Features of RCP and v2 for Particle Production at Intermediate pT

5) Emerging Physical Scenario and Future Experimental Verification

Formation of High Energy Density Matter

Experimental Evidences

1) Suppression of high transverse momentum particles and disappearance of back-to-back angular correlations energy loss while traversing the dense medium

the energy loss also contributing to the production of soft particles correlated with the high pT particle

-- Fuqiang Wang’s talk

2) Hydrodynamic features in particle productionand azimuthal angular distributions

high energy density in initial conditions !

Why Not QGP Yet?

High pT Phenomena – not directly sensitive to deconfinement though consistent with partonic state Hydrodynamical Behavior – not consistent with parton transport

picture, failed to describe the space-time

correlation (HBT) hadronization scheme dependent

Confinement Signature ?

Salient Feature of Strong Interaction

Asymptotic Freedom: Quark Confinement:

庄子天下篇 ~ 300 B.C. 一尺之棰，日取其半，万世不竭

Take half from a foot long stick each day,You will never exhaust it in million years.

QCD q q

q qq q

Quark pairs can be produced from vacuumNo free quark can be observedMomentum Transfer

Co

up

lin

g S

tren

gth

Shorter distance

(GeV)

The The Field & FeynmanField & Feynman picture of cascade fragmentation picture of cascade fragmentation

Kretzer@ISMD04

Too Many Baryons at Intermediate pT

Baryon Production from pQCD

K Kp p

e+e-jet fragmentation from SLD

Normal Fragmentation Cannot Produce the Large Baryon Yield

Geometry of Nucleus-Nucleus Collisions

Number of Participants

Impact Parameter

Npart – No of participant nucleonsNbinary – No of binary nucleon-nucleon collisions cannot be directly measured at RHIC estimated from Woods-Saxon geometry

Nuclear Modification Factors

ddp

Nd

collddpNd

TAA

T

pp

T

AA NpR 2

2

/)(

Use number of binary nucleon-nucleon collisions to gauge the colliding parton flux:

N-binary Scaling RAA or RCP = 1 simple superposition of independent nucleon-nucleon collisions !

Peripheralcoll

T

Centralcoll

TTCP

NddpNd

NddpNd

pR

]/[

]/[

)( 2

2

Particle Dependence of RCP

suppression

Elliptic Flow Parameter v2

y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Initial/final conditions, dof, EOS

1i

Ritttt

))ψcos(i(2v1dydpp

dN

2π

1

dyddpp

dN

STAR

PHENIX

Particle Dependence of v2

Baryon

Meson

Why saturation at intermediate pT ?Why baryon and meson difference ?

Strange quark dynamics are not significantly different from light quarks

STAR Preliminary

Salient Features at Inermediate pT

1)Why so many baryons versus mesons?

2)Why does elliptic v2 versus pT saturate ?

3)Why Rcp and v2 in two groups: Baryon and Meson ?

4)Why strange quark similar to light u/d quarks ?

Hadronization from bulk partonic matter – Constituent quark degrees of freedom Recombination/Coalescence scheme for hadron formation Surface emission

Constituent Quark Degree of Freedom

KS – two quark coalescence– three quark coalescence from the partonic matter surface?!

Particle v2 may be related to quark matter anisotropy !!

pT < 1 GeV/c may be affected by hydrodynamic flow !

Hadronization Scheme for Bulk Partonic Matter:

Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Rafelski+Danos, Molnar+Voloshin …..)

Quark Recombination – (R.J. Fries et al, R. Hwa et al)

Quark Cluster Formation from Strongly Interacting Partonic Matter

Volcanic mediate pT – Spatter (clumps)

Strangeness enhancement from QGP is most prominent in the region where particle formation from quark coalescence is dominant !

Multi-Parton Dynamics for Bulk Matter Hadronization

Essential difference:Traditional fragmentation particle properties mostly determined by the leading quark !Emerging picture from RHIC data (RAA/RCP and v2) all

constituent quarks are almost equally important in determining particle properties !

v2 of hadron comes from v2 of all constituent quarks !

Are constituent quarks the effective degrees of freedom for bulk partonic matter hadronization ? How do we establish signatures for multi-parton dynamics, recombination model for example, where thermal constituent quarks or shower partons from jet production are both possible ?

Future Measurements of QCD Properties of Bulk Matter

1) Quantitative Energy Loss of light/heavy Quarks

2) Where does the Energy Loss Go?

3) Strange and Charm Quark Dynamics from Bulk Matter

4) Fluctuations, Phase Transition and Critical Point

5) Initial Temperature of the Partonic System andIncoming Gluon Flux

Heavy Quark in QCD Medium

• Heavy Quark energy loss in color medium !

-- dead cone effect (less than light quarks)• Charm enhancement from high temperature

gluonic matter (Tinit > 500 MeV)!

An Intriguing Scenario ?!

PT

RAA

1.0

Light hadrons

Open Charm

(pT scale)

Require direct open charm measurement !

Energy Loss and Soft Particle Production

Leading hadrons

Medium

STAR PRELIMINARY

Fuqiang Wang’s work

A Critical Test for Recombination

Duke Group, PLB 587, 73 (2004)

pT Scale !!

And Strange Quark Dynamics in Bulk Matter

STAR will make a measurement of and v2 from run-4 Au+Au data !

Recombination DS/D0

PYTHIA Prediction

Charm quark recombines with a light (u,d,s) quark from a strangeness equilibrated partonic matter DS/D0 ~ 0.4-0.5 at intermediate pT !!!

pT Scales and Physical Processes

RCPThree PT Regions:

-- Fragmentation

-- multi-parton dynamics (recombination or coalescence or …)

-- Hydrodynamics (constituent quarks ? parton dynamics from gluons to constituent quarks? )

Summary

Formation of Dense Matter

Partonic Degrees of Freedom Important Hadronization of Bulk Partonic Matter

If So, the Dense Matter Must Be Deconfined

Is It QGP?

Discoveries from Unexpected Areas?!

RHIC -- Frontier for bulk partonic matter formation (quark clustering and rapid hadronization) -- Factory for exotic particles/phenomena

Potential exotic particles/phenomena:penta-quark states (uudds, uudds!)

di-baryonsH – (, uuddss) [] (ssssss)

strange quark matter

meta-stable Parity/CP odd vacuum bubblesdisoriented chiral condensate……

The End

Two Particle Jet-like Correlations

Jet-like two particle correlations (e.g., trigger particle 4-6 GeV/c, associated particle 2-4 GeV/c) :

These correlations cannot be easily explained in terms of recombination/coalescence scenario !

But 1) the effect of resonances on the two particle correlations has not be adequately addressed 2) trigger biases – with two high pT particles the initial parton is considerably harder than if only one high pT particle

is produced. Fragmentation region pT > 5.5 GeV/c 3) low level two particle correlations in the soft region can be

accommodated in recombination/coalescence(wave induced correlation?)

The Melting of Quarks and Gluons-- Quark-Gluon Plasma --

Matter Compression: Vacuum Heating:

High Baryon Density-- low energy heavy ion collisions-- neutron starquark star

High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang

Deconfinement

Global ObservablesPRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03)

PHOBOS

hminus:Central Au+Au <pT>=0.508GeV/cpp: 0.390GeV/c

Pseudo-rapidityWithin ||<0.5 the total transverse momentum created is 1.5x650x0.508 ~ 500 GeV from an initial transverse overlap area of R2 ~ 153 fm2 !

Energy density ~ 5-30 0 at early time =0.2-1 fm/c !

19.6 GeV

130 GeV200 GeV

Hydrodynamics Work at Low pT

Thermostatistical model also describe the particle ratios well ! -- Another indication for constituent quark degrees of freedom?

Charm and Bulk Matter

Does Charm Flow?Thermalization of partonic matter -- charm elliptic flow v2 ! -- charm hadron chemistry !

Simulation by X. Dong

Charm Meson v2 has to come from light quark v2

and possibly charm quark v2 !

Recombination and Two-particle Jet-like Correlation

Jet-like two particle correlations (e.g., trigger particle 4-6 GeV/c, associated particle 2-4 GeV/c) :

These correlations cannot be easily explained in terms of recombination/coalescence scenario !

But 1) the effect of resonances on the two particle correlations has not be adequately addressed 2) trigger biases – with two high pT particles the initial parton is considerably harder than if only one high pT particle

is produced. Fragmentation region pT > 5.5 GeV/c 3) low level two particle correlations in the soft region can be

accommodated in recombination/coalescence(wave induced correlation?)