Heavy Quark Probes of QCD Matter at RHIC

Huan Zhong Huang

University of California at Los Angeles

ICHEP-2004

Beijing, 2004

Outline

1) Experimental Evidences for Bulk MatterHadronization

2) Recombination for Heavy Quark Mesons

3) Future Measurements of Heavy QuarkProduction Features at RHIC

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

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

STAR

PHENIX

Particle Dependence of v2

Baryon

Meson

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

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 ?

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 ?

Fragmentation vs RecombinationFragmentation Function z = phadron/pparton < 1

Recombination Scheme phadron = pparton-1 + pparton-2 … Z >= 1

Fragmentation Functions from e+e Collisions

Belle Data

Charm Mesons from Hadronic Collisions

Charm meson pT ~ follow the NLO charm quark pT

-- add kT kick -- harder fragmentation ( func or recombination scheme)

kT Kick? What about kL?

The xF distribution matches the NLO charm quark xF !

The RHIC D meson pT ~ NLO charm quark too

NLO pQCD predictions are provided by R. Vogt, hep-ph/0203151

STAR Preliminary

But NLO QCD calculation fits CDF data within a factor of 2

Recombination mechanism for D formation ?!

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? )

PT scale for heavy quarks?

Summary

Formation of Dense Matter

Partonic Degrees of Freedom Important Hadronization of Bulk Partonic Matter

Heavy Quark Measurement One of the Key Future Critical Test of Multi-parton Dynamics for Hadronization

Signature for Deconfinement !

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?)

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 !

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

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 !

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

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

Kretzer@ISMD04

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 !