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Evidence for Multi-parton Dynamics in Hadronization of Bulk Partonic Matter at RHIC

Huan Zhong Huang (黄焕中 )Department of Physics and Astronomy

University of California Los Angeles

Department of Engineering PhysicsTsinghua University

7th Annual Conference of Chinese High Energy Physics Society

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Outline

• Relativistic Heavy Ion Collider (RHIC) and Quark-Gluon Plasma (QGP)

• Fragmentation Scheme • Hadronization of Bulk Partonic Matter• Recent Results of High pT Probes• Outlook

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STAR

Relativistic Heavy Ion Collider --- RHIC

Au+Au 200 GeV N-N CM energyPolarized p+p up to 500 GeV CM energy

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Quark-Hadron Phase Transition

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Au + Au Collisions at RHIC

STARSTAR

Central Event

(real-time Level 3)

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Nucleus-Nucleus Collisions and Volcanic Eruption

Volcanic high pT -- Strombolian eruption Volcanic mediate pT – Spatter (clumps)

Volcanic low pT – Bulk matter flows

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

Kretzer@ISMD04

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Baryon Production from pQCD

K Kp p

e+e-jet fragmentation from SLD

Normal Fragmentation Cannot Produce the Large Baryon Yield

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Too Many Baryons at Intermediate pT

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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

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Elliptic Flow: ultra-cold Fermi-GasElliptic Flow: ultra-cold Fermi-Gas

• Li-atoms released from an optical trap exhibit elliptic flow analogous to what is observed in ultra-relativistic heavy-ion collisions

Elliptic flow is a general feature of strongly interacting systems!

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Hydro calculations break-down at higher pT (as expected).

How is v2 established at pT above 2 GeV/c?

Why is baryon v2 larger than meson v2?

PRL 92 (2004) 052302; PRL 91 (2003) 182301

Elliptic Flow v2

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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)

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Constituent Quark Scaling

Constituent (n) Quark Scaling-- Meson n=2 and Baryon n=3 grouping

Some deviation due to internal hadron structure

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Nuclear Modification Factor

ddp

Nd

collddpNd

TAA

T

pp

T

AA NpR 2

2

/)(

Peripheralcoll

T

Centralcoll

TTCP

NddpNd

NddpNd

pR]/[

]/[

)( 2

2

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

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Strangeness from Bulk Partonic MatterRCP

Constituent Quark Number Scaling-- Hadronization through quark clustering-- Effective DOF – constituent quarks quasi-hadrons at Tc ? Lattice QCD picture?

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Intermediate pT Dynamics

Multi-parton dynamics – clustering of quarks – could be responsible for -- increased baryon production -- strange baryon enhancement -- strong elliptic flow at intermediate pT !!!

Hadronization of bulk partonic matter -- different phenomenon from e+e- collisions !

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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? )

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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 !

The fact that in order to explain the v2 of hadrons individual constituent quarks (n=2-meson,3-baryon) must have a collective elliptic flow v2 and the hadron v2 is the sum of quark v2 Strong Evidence for Deconfiement !

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Recombination+Fragmentation ModelRecombination+Fragmentation Model

basic assumptions:

• at low pt, the quarks and antiquark spectrum is thermal and they recombine into hadrons locally “at an instant”:

features of the parton spectrum are shifted to higher pt in the hadron spectrum

• at high pt, the parton spectrum is given by a pQCD power law, partons suffer jet energy loss and hadrons are formed via fragmentation of quarks and gluons

qq M qqq B

• shape of parton spectrum determines if recombination is more effective than fragmentation• baryons are shifted to higher pt than mesons, for same quark distribution understand behavior of baryons!

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High pT Phenomena at RHIC

Very dense matter has been created in central Au+Au collisions!

This dense matter is responsible for the disappearance of back-to-back correlation and the suppression of high pT particles !

Is the energy loss due to parton or hadron stage?Is there a noticeable difference in experimental phenomenon related to quarks versus gluons?

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The Suppression is the Same for and – parton level effect

No suppression for direct photons – photons do not participant !

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No Significant Difference BetweenQuarks and Gluons at High pT

Baryons more likely from gluon fragmentations in the pQCD region

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STARSTAR

No Significant Difference BetweenHeavy Quark Meson and Light Quark Mesons

Non-photonic electrons from heavy quark decays

Charged hadrons

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Heavy quark energy loss: Early Expectations

k

E

M

dP

k

dkkdCdP Fs

,

)/1()(

0

2220

022

022

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Y. Dokshitzer & D. Kharzeev PLB 519(2001)199

Radiative energy loss of heavy quarks and light quarks

--- Probe the medium property !

Heavy quark has less dE/dx due to suppression of small angle gluon radiation

“Dead Cone” effect

M. Djordjevic, et. al. PRL 94(2005)112301

J. Adams et. al, PRL 91(2003)072304

What went wrong?

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B and D contributions to electrons

Experimental measurement of B and D contributions to non-photonic electrons !

Direct measurement of D and B mesons

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Poor (Wo)Man’s Approach to Measure B/D Contributions to Electrons – e-h correlations

B

D

PYTHIA Simulations of e-h correlations from p+p

X. Lin hep-ph/0602067

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STAR preliminary data motivated sonic-boom prediction

F. Wang (STAR), QM’04 talk, nucl-ex/0404010.Now published: STAR, PRL 95, 152301 (2005).

pTtrig=4-6 GeV/c, pT

assoc=0.15-4 GeV/c

Many recent studies:H. Stoecker, nucl-th/0406018.Muller, Ruppert, nucl-th/0507043.Chaudhuri, Heinz, nucl-th/0503028.Y.G. Ma, et al. nucl-th/0601012.

Casalderrey-Solana, Shuryak, Teaney, hep-ph/0411315

Actually sonic-boom was first predicted in the 70’s by the Frankfurt school.

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High pT Phenomena at RHICVery dense matter has been created in central Au+Au collisions!

This dense matter is responsible for the disappearance of back-to-back correlation and the suppression of high pT particles !

The mechanism for parton energy loss is yet to be understood !

The nature for the broad peak on the away-side requires more studies (Mach cone or not) !

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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……

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STAR – Exciting Physics Program A full TOF upgrade will greatly enhance STAR’s capability !!

RHIC – Exotic Particle Factory

Full Barrel TOF Using MRPC

Chinese STAR Group SINAP Tsinghua University USTC CCNU, Wuhan IMP, Lan Zhou IHEP

Construction to be finished by 2008Full installation in 2009

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RHIC Physics Outlook

Heavy Ion Physics: 1) Properties of high density QCD matter 2) Chiral symmetry at high temperature and density 3) Search for exotic particles/phenomena at RHIC 4) Search for critical point (low energy scan)

RHIC Spin Physics Using Polarized p+p Collisions: 1) the gluon spin structure function major milestone to understand the spin of the proton! 2) sea quark spin structure function 3) quark transverse spin distribution

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End of Talk

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Experimental Statistical and Systematic Errors

c-cbar production CS PHENIX0.92+-0.15+-0.54 mb0.567+-0.057+-0.224 mb

STAR1.4+-0.2+-0.4 mb

Errors taken seriously

High pT region does not contribute to total CS much. Difference between STAR and PHENIX has to be resolved !!

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B does not seem dominant at pT 4.5 GeV/c

Preliminary STAR Data

Xiaoyan Lin – STAR presentation at Hard Probe 2006

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Intriguing Situation Regarding Pentaquark States

pK+ and pK- from 18.4 M d+Au at 200 GeVBackground – Combinatorial and Correlated Pairs

Statistical significance ~ 4Intriguing ! Not conclusive yet !Another long d+Au run will resolve this uncertainty !

M (GeV/c2) M (GeV/c2)

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Intermediate pT Region

Volcanic mediate pT – Spatter (clumps)

At RHIC intriguing experimental features: multi-quark clustering enhanced baryon over meson production strangeness equilibration increased multi-strange hypeons

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Radiative Energy Loss not EnoughMoore & Teaney, PRC 71, 064904 (2005)

Large collisional (not radiative) interactions also produce large suppression and v2

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Charm Quark in Dynamical Model (AMPT)

Large scattering cross sections needed !

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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

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STAR

PHENIX

Particle Dependence of v2

Baryon

Meson

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

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Spin Physics Program

The Spin Structure of the Proton:

½ = ½ q + G + <L>

q up, down and strange quarksG gluonsL angular momentum of quarks and gluons

Experimentally: 1) total spin in quarks ~ 30% 2) sea quarks are polarized too 3) little info about the gluon polarization 4) even less know about <L> and how to measure <L>