1 STAR results on Medium Properties and Response of the Medium to Energetic Partons Bedanga Mohanty (For the STAR Collaboration) Variable Energy Cyclotron.

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STAR results on Medium Properties and Response of the Medium to Energetic

PartonsBedanga Mohanty

(For the STAR Collaboration)Variable Energy Cyclotron Centre, Kolkata

Motivation Parton Energy Loss Medium Response to Energetic Partons Summary

Outline

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Motivation

Azimuthal anisotropy Partonic collectivity, viscosity and interactions

Collectivity and Thermalization

Identified particle correlations

Parton recombination, modified/vacuum fragmentation

Medium effect on particle production mechanism

High pT particle production and correlations, correlations with respect to reaction plane

Non-Abelian features of QCD - Color factor effects, path length effects of Eloss

Jet-medium coupling

Partonic interactions

Mechanism of Eloss

3-particle correlationsMach conesVelocity of sound

High pT particle production, and correlations

Parton Eloss in the mediumEnergy density

Experimental probesPhysical phenomenonMedium properties

Correlations play a significant role in understanding medium properties

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Basic Approach

Look for modification

Is there any modification in heavy ion collisions ?

Calibrated probe

Near side Leading/trigger particle

Away side

near away

Associated particles

Absence ofmedium

STAR : PRL 97 (2006) 252001STAR : PLB 637 (2006) 161

Medium formed in heavy-ion collisions

Jet and high pT particle production in pp understood in pQCD framework

Higher the trigger particle pT more probable it is from a jet and more well defined is the jet axis

STAR Preliminary

New STAR high pT p+p results

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Advantage of Di-hadron Correlations

y (fm)

x (fm)Less surface bias

Single Di-hadron

y (fm)

x (fm)

Limited sensitivity of RAA to P(E,E)T. Renk, PRC 74 (2006) 034906

T. Renk and Eskola,hep-ph/0610059

Di-hadron correlations more robustprobes of initial density ~

H. Zhong et al., PRL 97 (2006) 252001

2IAA

2RAA

fmq 2GeV3.08.2~ ﾱ

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Current Observations in STARAway side yield modification

What does these features reveal about the medium ?

Parton Eloss

High pT suppression

STAR : PLB 655 (2007) 104STAR : PRL 97 (2006) 152301STAR : PRL 91 (2003) 072304

Reappearance of di-jets

STAR : PRL 97 (2006) 162301

pTlp : 4 - 6 GeV/c

pTasoc : 2 GeV/c - pTlp

Away side shape modification

d+Au

Enhanced correlated yield at large on near side

Medium response

STAR : J. Putschke, QM2006STAR : M. J. Horner, QM2006

2.5 < pT

trig< 4 GeV/c

1< pT

assoc < 2.5 GeV/c

pTtrig=3-6 GeV/c,

2 GeV/c <pTassoc< pT

trig

Au+Au

STAR: PRL 95 (2005) 152301J.G. Ulery, QM 2005

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Do they give answers to …

Mechanism of energy loss in medium -

What is the Path length dependence of energy loss ? - L2 or LDo we see a Color charge dependence of energy loss ?

What is the probability distribution of parton energy loss ?Do partons loose energy continuously or discretely?

Where does the energy from the absorbed jets go or how are they distributed in the medium?

- Shock waves in recoil direction - Coupling of radiation to collective flow

Few hard interactions or multiple soft interactions ?

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Results on Partonic Eloss

Parton Eloss Reappearance of di-jetsMedium response

Is there a difference in quark and gluon Eloss ? Patricia Fachini (Parallel Talk on 5th Feb), Zhangbu Xu (Plenary Talk on 5th Feb)

Path length effects of parton Eloss : Dihadron Fragmentation functions Oana Catu (Parallel talk on 8th Feb)

Di-hadron correlations with respect to reaction plane Aoqi Feng (Parallel Talk on 5th Feb)

Probability distribution of parton Eloss : -hadron correlations A. Hamed (Parallel Talk on 8th Feb)

Results to be discussed in this talk :

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Is there a difference in q, g Eloss

Color factor effects of the type 9/4 not observed in pion, (anti-)proton ratios and Rcp upto pT ~ 12 GeV/c

STAR : PLB 637 (2006) 161 STAR : PRL 97 (2006) 152301 STAR : PLB 655 (2007) 104

Patricia Fachini, Parallel Talk, 5th February

Baryon & meson NMF

STAR Preliminary

Anti-Baryon to meson ratio

STAR Preliminary

EgEq

~ 9/4

Anti-particle to particle ratio

X.-N. Wang,PRC 70 (2004) 031901

STAR Preliminary

2 L<q>

CE s ^

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Away-side Di-hadron Fragmentation Function

Oana Catu, Parallel Talk, 8th February

zT=pTassoc/pT

trig

Denser medium in central Au+Au collisions compared to central Cu+Cu zT distributions similar for Au+Au and Cu+Cu for similar Npart

STAR Preliminary

STAR Preliminary

1/N

trig d

N/d

z T

IAA

zT

6< pT trig < 10 GeV

Inconsistent with PQM calculations Modified fragmentation model better

STAR Preliminary

H. Zhong et al., PRL 97 (2006) 252001

C. Loizides, Eur. Phys. J. C 49, 339-345 (2007)

Npart

IAA

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Aoqi Feng, Parallel Talk, 5th February

Di-hadron Correlations w.r.t Reaction Plane

out-of-plane S=90oin-plane S=0 3< pTtrig < 4 GeV/c,

pTasso : 1.0- 1.5 GeV/c

trigger in-plane

trigger out-of-plane

20-60% : away-side : from single-peak (φS =0) to double-peak (φS =90o) Top 5% : double peak show up at a smaller φS

At large φS, little difference between two centrality bins

Observations :

Au+Au 200 GeV

STAR Preliminary

STAR Preliminary

d+Au

20-60%

top 5%

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Path Length Effects

Au+Au 200 GeV

3< pTtrig < 4 GeV/c

1.0 < pTasso < 1.5 GeV/c

in-plane:

similar to dAu in 20-60%.

broader than dAu in top 5%.

Out-of-plane:

not much difference between the two centrality bins.

Away-side features reveal path length effects

Aoqi Feng, Parallel Talk, 5th February

RMS =i ( i - )2 yi

i yi

RMS

STAR Preliminary

v2{4}

v2{RP}

v2 sys. error

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Eloss probability distribution : -hadron correlation

QuickTime and aﾪTIFF (Uncompressed) decompressor

are needed to see this picture.

Provides constraints on Eloss probability distributions Possibly gives full accounting of jet energy loss

T. Renk : PRC 74 (2006) 034906

Jet

Prompt

1st measurement of away-side -h correlations Suppression similar level as inclusives in central collisions Note : Ejet = E

A. Hamed (Parallel Talk on 8th Feb)

X.-N. Wang et alPRL 77(1996)231

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Results on Medium Response

Parton Eloss Reappearance of di-jetsMedium response

Results to be discussed in this talk : Conical Emission : Final 3-particle results with higher pT trigger, PID correlations

Jason Ulery (Plenary Talk on 8th Feb), Gang Wang (Parallel Talk on 8th Feb), Guoliang Ma (Poster), Jiaxu Zuo (Poster), Quan Wang (Poster)

Ridge in heavy ion collisions : Identified particle correlations, 3-particle correlations Correlations w.r.t RP

Pawan Netrakanti (Plenary Talk on 5th Feb), Aoqi Feng, Parallel Talk, 5th Feb,Christine Nattrass (Parallel Talk on 8th Feb), Jiaxu Zuo (Poster), Cristina Suarez (Poster), Betty Abelev (Poster) , Navneet Kumar (Poster)

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Two component approach -Correlated to trigger (jets..)- Uncorrelated to trigger (except via anisotropic flow)Bkg normalization 3-particle ZYAM

STAR Preliminary

Conical emission or deflected jets ?

Conical Emission

Mediumaway

near

deflected jets

away

near

Medium

Conical Emission

Experimental evidence of Conical emission

See also Jason Ulery - Plenary Talk on 8th February,

(1-2)/2

(1-2)/2

3 <pT-trig < 4 GeV/c1 < pT-assoc < 2 GeV/c

Gang Wang (Parallel Talk on 8th Feb

e-h correlation

STAR Preliminary

dAu

Central Au+Au 0-12%

STAR Preliminary

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Mach Cone or Cerenkov Gluons

Mach-cone:

Angle independent of associated pT

Cerenkov gluon radiation:

Decreasing angle with associated pT

Naively the observed cone angle ~ 1.36 radians leads to very small (time averaged) velocity of sound in the medium

STAR Preliminary

Strength and shape of away side structures observed depends on assumed magnitude of flow coefficientsIn cumulant approach: no conclusive evidence for conical emission so farClaude Pruneau : STAR : QM2008(Poster), PRC 74 (2006) 064910

C3

Subtraction of v2v2v4 termsusing on v2 = 0.06

Subtraction of v2v2v4 term using v2 = 0.12

STAR PreliminaryCon

e an

gle

(rad

ians

)

pT (GeV/c)

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Ridge in Heavy Ion Collisions

What does these features reveal about the medium ?Perhaps tells us how the energy lost by partons are distributed

in the medium

d+Au, 40-100% Au+Au, 0-5%

3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

d+Au

Au+Au

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Features of the Ridge (at QM2006)

Yield at large independent on

Indication of two contributionsJet contribution + contribution arising due to jet

Propagating in the medium

What could be the different physics possibilities ?

STAR Preliminary

Ridge persists up to high pT-trigTRidge ~ Tinclusive < Tjet

STAR Preliminary

STAR Preliminary

STAR : J. Putschke, QM2006

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Different Physics Possibilities

Qualitatively consistent with the features of ridge

Following are the new approaches attempted to disentangle different physics possibilities- 3-particle correlation- Identified particle correlation - Di-hadron correlation with respect to reaction plane- System size dependence

QCD bremsstrahlung radiation boosted by transverse flow S.A.Voloshin, Phys.Lett.B. 632(2007)490E.Shuryak, hep-ph:0706.3531

Broadening of quenched jets in turbulent color fields A.Majumder et.alPhys. Rev. Lett.99(2004)042301

Recombination between thermal and shower partons at intermediate pTR.C. Hwa & C.B. Chiu Phys. Rev. C 72 (2005) 034903

In medium radiation and longitudinal flow pushN.Armesto et.al Phys.Rev.Lett.93(2007) 242301

Momentum Kick ModelC.Y. Wong hep-ph:0712.3282

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Jet and Ridge : Observations

Near-side jet yield independent of colliding system, Npart

and trigger particle type High pT-trigleads to higher jet yields Supports : Parton fragmentation after parton Eloss in the mediumRidge yield increases with Npart

Oana Catu, Parallel Talk, 8th February Christine Nattrass, Parallel Talk, 8th February

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Particle Ratios and v2 : Jet & Ridge

Cristina Suarez - Poster,

Ratios in cone smaller than inclusive Ratios in ridge similar to inclusive

Jet : /K0s ~ 0.5 < inclusive

Ridge : /K0s ~ 1 ~ inclusive

Jiaxu Zuo - Poster

Ridge vs. Inclusive

STAR Preliminary

Jet Cone vs. Inclusive

STAR Preliminary

Jet

ridge

Paul Sorenson - Talk 9th Feb, Navneet K. Pruthi - Poster

v2 modulated background + ridge + jet

inferred v2 of events with ridge pair ~ inclusive inferred v2 of events with jet pair < inclusive

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Ridge : Di-hadron Correlation w.r.t RP

jet

ridge

Observations :

Ridge: decreases with φS. Little ridge at larger φS.

Jet: slightly increases with φS. General agreement with d+AuInterpretation :

Strong near-side jet-medium interaction in reaction plane, generating sizable ridge

Minimal near-side jet-medium interaction perpendicular to reaction plane

Aoqi Feng, Parallel Talk, 5th February

STAR Preliminary

3< pTtrig < 4 GeV/c,

pTasso : 1.0- 1.5 GeV/c

Au+Au 200 GeV

20-60%

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Uniform overall excess of associated particles not due to correlated emission

+ =

Ridge : 3-particle Correlation In-medium radiated

gluons diffused inJets

Pawan K. Netrakanti, Plenary Talk, 5th February

In-medium radiated gluons still collimated

Jet fragmentation anddiffused gluons

dAu : Jets AuAu : 200 GeV

3<pTTrig<10 1<pT

Asso<3 ||<0.7

STAR Preliminary

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Outlook : Di-Jets and Jet Reconstruction

Parton Eloss Reappearance of di-jetsMedium response

Results to be discussed in this talk :

Di-jets triggered correlations - Olga Barannikova, Parallel Talk on 8th February

Multi-hadron cluster triggered correlations Brooke Haag - Poster

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Observation of di-jets

Di-Jets Triggered Correlations

Di-jet trigger

T2

A1

T1

What happens to thesefeatures if we trigger on di-jets ?

T1: pT>5GeV/c

T2: pT>4GeV/c A1: pT>1.5GeV/c

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Di-Jets Triggered Correlations

Au+Au 12% central

||<0.7

T2A1_T1T1A1_T2

-1-1.5 0 1-0.5 0.5 1.5

1

_d

N_

Ntr

ig d

)

STAR Preliminary

0

No Away-side suppression, No Shape modification, no ridge Olga Barannikova, Parallel Talk, 8th February

200 GeV Au+Au, 12% central

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

T2A1_T1

T2A1

-1-2 0 1 2 3 4 5

2

0 1

_d

N_

Ntr

ig d

)

-2

4

STAR Preliminary

12% Central40-60% MB60-80% MB

T2A1_T1

STAR Preliminary

Au+Au

d+Au

-1-2 0 1 2 3 4 5

1

0

1

_d

N_

Ntr

ig d

)

STAR Preliminary

2

3

200 GeV Au+Au & d+Au

1

_d

N_

Ntr

ig d

)

Multi-hadron Cluster Triggered Correlations

RSeed

Secondary Seeds

Associated track

Multi-hadron trigger

Motivation: Explore jet-biases in di-hadron correlations Start developing jet reconstruction

Use cluster energy for trigger:- R = 0.3- p

T,seed > 5 GeV

- pT,sec seed

> 3 GeV

Away-side spectrum

Single-hadron and multi-hadron triggers give similar resultRe-confirms single high pT triggered correlation resultsprobes jet-like correlations

0-12% Au+Au

Add 12-15 GeV trigger

STAR Preliminary

Brooke Haag - Poster

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Summary : Parton Eloss

Differences (due to color factor) in energy loss between

quarks and gluons not observed in the measured pT range

Dense medium formed in Au+Au collisions compared

to central Cu+Cu collisionsCu+Cu and Au+Au : zT distributions similar for collisions

with similar Npart - feature not consistent with PQM

calculationsPath length effects observed : Broader RMS for away-side

distribution in di-hadron correlations from in-plane to

out-of-plane

1st measurement of away-side suppression

in -h correlation

STAR Preliminary

STAR Preliminary

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Jet Cone vs. Bulk

Summary : Medium ResponseStrong jet-medium interaction observed.Signals of conical emission observed in central Au+Au

Collisions at 200 GeV in 2-component approach Medium responds through ridge formation. New observations should provide significant constrains on the

mechanism of ridge formation o Particle ratios in ridge similar to inclusive measurementso Di-hadron correlations with respect to reaction plane

indicates - ridge is dominated in-plane, consistent with

medium density effect

o 3-particle correlations : jet fragmentation + an overall uniform

excess of associated particles not due to correlated emission

Ridge vs. Bulk

STAR PreliminarySTAR Preliminary

STAR Preliminary

STAR Preliminary

STAR Preliminary

STAR Preliminary

dAu AuAu

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ThanksThanks to STAR Collaboration

Argonne National LaboratoryInstitute of High Energy Physics - BeijingUniversity of BirminghamBrookhaven National LaboratoryUniversity of California, Berkeley University of California - DavisUniversity of California - Los AngelesUniversidade Estadual de CampinasCarnegie Mellon UniversityUniversity of Illinois at Chicago Creighton University Nuclear Physics Inst., Academy of SciencesLaboratory of High Energy Physics - DubnaParticle Physics Laboratory - DubnaInstitute of Physics. BhubaneswarIndian Institute of Technology. MumbaiIndiana University Cyclotron Facility Institut Pluridisciplinaire Hubert CurienUniversity of Jammu Kent State UniversityUniversity of KentuckyInstitute of Modern Physics, LanzhouLawrence Berkeley National Laboratory Massachusetts Institute of TechnologyMax-Planck-Institut fuer PhysicsMichigan State University

Moscow Engineering Physics Institute City College of New YorkNIKHEF and Utrecht UniversityOhio State UniversityPanjab UniversityPennsylvania State University Institute of High Energy Physics - ProtvinoPurdue UniversityPusan National UniversityUniversity of RajasthanRice UniversityInstituto de Fisica da Universidade de Sao PauloUniversity of Science and Technology of China Shanghai Institue of Applied PhysicsSUBATECHTexas A&M UniversityUniversity of Texas - AustinTsinghua UniversityValparaiso University

Variable Energy Cyclotron Centre. Kolkata

Warsaw University of TechnologyUniversity of Washington

Wayne State University

Institute of Particle PhysicsYale University University of Zagreb

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Color Factors and q,g Eloss

i,j represent fermion field indices and a,b gauge field indices

QCD : For SU(3) : Nc = 3 CA = 3 (gluons), CF = 4/3 (quarks)

SU(3) is the gauge group for QCD

S = 0.119

Eg

Eq~ 9/4

2 L<q>

CE s ^

An opportunity to relate experimental observable (of Eloss) to basic ingredient of QCD - Gauge Group through Color Factors

ALEPH : ZPC 76 (1997) 1OPAL :EJPC 20 (2001) 601