Multi-Parton Dynamics at RHIC

Huan Zhong Huang

Department of Physics and Astronomy

University of California Los Angeles

@ShanDong University

Oct. 17 2003

Outline

1) Experimental Observations at Intermediate pT

2) Multi-parton Dynamics

-- coalescence/recombination picture

-- possible gluon junction interaction

3) Hydrodynamics and pQCD

4) Mass Dependence in Cronin Effect

5) Outlook

Intermediate pT Region

Volcanic mediate pT – Spatter (clumps)

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

y

Dynamical Origin of Elliptic Flow

STAR PreliminaryAu+Au 200 GeV

V2 in the intermediate pT region: Dynamics for Saturation ? Particle Dependence of v2 ?

Collective Pressure

High pressure gradientLarge expansion velocity

Small expansion velocity

pT dependent !

Surface Geometrical Phase Space

Surface Emission PatternHigh particle density

Low particle density

pT independent ! orpT dependence may comefrom surface thickness (pT)

x

What Determines the pT Dependence ?

v2

Particle production steep func of pT

V2 little pT dependence 2<pT<5 GeV/c

Charged hadron elliptic flow

STAR

PHENIX

What Determines the Particle Dependence ?

Baryon

Meson

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

So Many Baryons !!

•Two component shape evident in the KS spectra.

•The Λ yield exceeds the KS yield at intermediate pT.

•The Λ yield is most enhanced in central collision.

What Determines the Baryon-Meson Yield?

RCP=[yield/N-N]central

[yield/N-N]peripheral

RCP ~ 1 particle production proportional to the number of binary nucleon-nucleon collisions – superposition of independent of n-n collisions.

Intermediate pT region special !!

Surface Model Alone Does not Work

more opaque:fewer

particles

less opaque:more particles

Neither Woods-Saxon nor Hard-Sphere distribution canmatch the v2 magnitude readily with standard fragmentation for particle formation !

Multi-Parton Dynamics

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,Molnar+Voloshin …..)

Quark Recombination – (R.J. Fries et al….)

STAR+PHENIX

Nuclear Modification Factor RAA RCP

Multi-parton dynamics predict baryon yield increases with centrality FASTER than mesons! Yield ~ n and n>nK a feature not present in single parton fragmentation !

Multi-parton dynamics: coalescence, recombination and gluon junctions.

RCP

RCP=[yield/N-N]central

[yield/N-N]peripheral

Strangeness from Bulk Partonic Matter

Strangeness enhancement is most prominent at intermediate pT from quark coalescence in an equilibrated bulk matter !

Recombination versus Coalescence

Standard Fragmentation Scheme – leading parton fragments into hadrons quarks from pair production out of vacuum.

Recombination Model -- R. Hwa et al … original recombination idea -- Recent Fries et al… for heavy ion collisions leading parton from pQCD processes recombined with soft partons from thermalized quarks/gluons.

Coalescence Model thermalized quarks (gluons) coalescence form hadrons.

Flavor Correlations and Dynamical Transition

Interesting Measurements

C. Nonaka et al nucl-th/0308051

hydro

at high pT !!Open Charm !!STAR TOF Upgrade !

Intermediate pT Dynamics

• Identified particle spectra and elliptic flow at intermediate pT are unique probes of multi-parton dynamics for particle formation – clustering of quarks!

• Strangeness equilibration of the bulk partonic matter may also reflect in the enhanced strange baryon production from quark clusterings.

The dynamics at the intermediate pT can be the key to a phenomenological hadronization description of bulk partonic matter!

The to Ratio

@mid-rapidityPb+Pb @SPSMany more sThan s !!

Scenarios of Baryon Number Transport

Direct Transport Through Gluon Junctions …

X)

Indirect Transport Through Pair Production Modified by Baryon Chemical Potential …

and K

and K

and p / n ) K

Net Baryon Density Increases the Associated Production and Transfers net baryon number to multiply-strange baryons !

Multi-parton Dynamics and Baryon Production

q

qq

q

q q

Baryon Anti-Baryon

Baryon (Hyperon) Production may be Enhanced by Gluon-Junction Interaction Dynamics:

Gluon Junction Mechanism -- (Kharzeev, Gyulassy and Vance ….)

Junction

Event-by-Event STAR Hyperon Correlations Doable with STAR TOF and SVT Upgrade !

Measure local baryon and anti-baryon quantum number correlations in pT-y space !

Hydrodynamics at Intermediate pT?

At intermediate pT, RCP of K0S is

lower than that of LambdaHydro/p-QCD: mass effectQuark coalescence: Particle type effectNeed !!!

RCP of close to that of K0S other

than that of LambdaParticle production at intermediate pT region is driven by the particle’s type, not the mass

Hydrodynamics fails at intermediate pT

no v2 saturation Particle dependence of v2 and RAA(RCP)

Higher statistics data from d+Au is being analyzed by Xiangzhou Cai from SINR.Future Au+Au data + TOF upgrade !!

Particle Dependence in Cronin Effect Significant at Low Energy

P.B. Straub et al., PRL 68 452 (1992)p+A collisions at sqrt(s) = 38.8 GeV

Strong particle dependence proton > kaon > pion

No significant particle and anti-particle difference ! no valence quark effect ! The Cronin effect is expected to decrease with beam energy !

p p

K+ K-

RW/Be

Traditional Cronin Effect is not the whole story at RHIC

STAR d+Au from TOFr analysis (USTC+BNL+RICE)Results on KS, and will reach higher pT (SINR+UCLA)

Nuclear Modification Factor Rcp

At intermediate pT, RCP of K0

S is lower than that of Lambda

p-QCD: mass effectQuark coalescence: Particle type effect

RCP of is closer to K0S

than LambdaParticle production at intermediate pT region is dividing by the particle’s type, not the mass

The ratio of central (top 20%) over peripheral (100-40%) (RCP) normalized by <Nbin>, vs. transverse momentum. <Nbin>|cent=14.18; <Nbin>|periph=3.34

STAR Preliminary

Xiangzhou Cai

Outlook

Intermediate pT very special !!

Multi-parton dynamics --- coalescence --- recombinations --- gluon junction interactions

Hadronization phenomenology of bulk partonic matter

Particle dependence of Cronin effect

Identified Particle Spectra and Elliptic Flow !!(J/, and D mesons) STAR TOF/microSVT detector upgrade essential !