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Recent Results from RHIC

Huan Zhong Huang黄焕中

Department of Physics and AstronomyUniversity of California Los Angeles

Department of Engineering PhysicsTsinghua University

Mar 23, 2008 @CCAST

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Outline

• High pT and Heavy Quark Measurements

• Hadronization of Bulk Partonic Matter

• Outlook

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Hard Scattering and Jet Quenching

back-to-back jets disappear

leading particle suppressed

Hard Scattering in p+p Parton Energy Loss in A+A

Reduction of high pT particlesDisappearance of back-to-back high pT particle correlations

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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?What is the flavor dependence of energy loss?Particle emission pattern associated with E Loss?

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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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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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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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Does Charm Quark Flow Too ?

Reduce Experimental Uncertainties !!Suppression in RAA Non-zero azimuthal anisotropy v2 !

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B and D contributions compatible

Bottom quarks may suffer considerable energy loss in the dense partonic medium too !

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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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R.B. Neufeld

(preliminary)

u = 0.75 c

x (

rx)

mD2 T

x gz (

rx)

mD2 T

(z -

ut)

u = 0.99955 c

Mach cone in QCD vs. N=4 SYM

Chesler & Yaffe

arXiv:0712.0050

Energy Density Energy Flux

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In order to discriminate Mach-cone from deflected jets, one needs three-particle correlation.

away

near

Medium

mach cone

Mediumaway

near

deflected jets 1

2

0

0

1

2

0

0

01

221 2

0

1

21

2

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Conic Emission in 3-hadron Correlations

Au+Au 0-12%

(1-2)/2

Au+Au 0-12%

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Mach cone or Cerenkov gluons?Angle predictions:• Mach-cone:

Angle independent of associated pT

• Cerenkov gluon radiation:

Angle decreases with associated pT

STAR Preliminary

Con

e an

gle

(rad

ians

)

pT (GeV/c)

(1-2)/2

Au+Au 0-12%

Central Au+Au results consistent with Mach cone emission

Naive calc. of time averaged velocity of sound in medium:

cv , θcosv

cpartonM

parton

s

Cone angle ~ 1.36 radians cs = 0.2c ??!

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Reaction Plane Dependence3<pT

trig<4GeV/c & 1.0<pTasso<1.5GeV/c 20-60%STAR

At low pT region, study the medium response to jets- Away side (medium side): single double peaks- Near side (jet side): amplitude reduced

= associate - trigger (rad)

STAR—Aogi Feng (CCNU)

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Does Heavy Quark Energy LossGenerate Mach Cone Emission?

Trigger on non-photonic electrons from heavy quark decays --

Preliminary STAR data show a broadening peak at the away side !

AWAY SIDE

NEAR SIDE

200 GeV Cu+Cu

Pythia result

Gang Wang (UCLA)

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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 !

There is a conic emission of particles when partons lose energy in medium, but the nature of the conic emission yet to be determined!

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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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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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Strangeness from Bulk Partonic MatterRCP

ss

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

Jinhui Chen et al (SINAP)

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Au+Au@200GeV

Cu+Cu@200Gev

STAR Preliminary

pT (GeV/c)

At intermediate pT (sss) and (ss) should be dominated by bulk thermal quark coalescence – no jet contribution

(Hwa and Yang PRC 75, 054904 (2007))

It appears that thermal quark coalescences dominate the particle production below pT 4 GeV/c, for both central Au+Au and Cu+Cu collisions

Xiaobin Wang (Tsinghua U.) -- Jinhui Chen (SINAP) --

and production from coalescence

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Parton PT Distributions at Hadronization

If baryons of pT are mostly formed from coalescence of partons at pT/3 and mesons of pT are mostly formed from coalescence of partons at pT/2

)2/(

)3/(

)2/(

)3/(

T

T

T

T

p

pd

p

ps

and particles have no decay feeddown contribution ! decay contribution is smallThese particles have small hadronic rescattering cross sections

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Strange and down quark distributions

s distribution harder than d distributionperhaps related to higher s quark mass in partonic evolution

Independent Test – /s should be consistent with s quark distribution Yes !

Jinhui Chen et al (SINAP/UCLA)

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Test on s/d Quark Ratios

s/d quark ratios

=

=

yes! but with large uncertainties due to decay feeddown corrections in

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QCD Color Screening: (T. Matsui and H. Satz, Phys. Lett. B178, 416 (1986))

A color charge in a color medium is screened similar to Debye screening in QED the melting of J/.

c c Charm quarks c-c may not bindInto J/ in high T QCD medium

The J/ yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050)

Debye Screening of Color Charge -- quarkonium melting in QGP

J/’ and c will melt in high temperature Quark-Gluon Plasma !The melting temperatures for ’ and c are lower !J/ may not melt until the temperature is higher than 2Tc ?!

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J/ is suppressed, but the physical mechanism is not clear !

The pT, rapidity and Npart dependence of J/ production cannot be explained yet!

The suppression at forward rapidity seems to be larger than at mid-rapidity ! Note parton density should be higher at mid-rapidity.

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Suppression + Regeneration

Zhuang, Pengfei et al, Phys. Rev. Lett. 97:232301,2006

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Two Component Approach: X. Zhao and R. Rapp, hep-ph/07122407

J/ non-suppression at high pT

Zebo Tang (USTC)

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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 ! ---- Evidence for Deconfinement !!!

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

J/ suppression and regeneration – More accurate experimental data and elliptic flow of J/ !

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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 OutlookHeavy 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

FY2008 Run – d+Au until mid-Feb 4 weeks of p+p

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End of Talk

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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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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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Constituent Quark Scaling

STAR

PHENIX

Baryon

Meson

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

Saturation of v2 at Intermediate pT

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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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Charm Quark in Dynamical Model (AMPT)

Large scattering cross sections needed !

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s and d quark distributions physical AMPT model using string-melting and coalescence can fit v2

but fails pT spec Using our s-d quark distribution AMPT can fit pT spec

-- Early evolution important in determining quark distributions!

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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>

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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