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Jet medium interactions Pawan Kumar Netrakanti

(For the STAR Collaboration)Purdue University, USA

Motivation Parton energy loss Medium response to energetic partons Summary

Outline

Workshop on Hot & Dense Matter in the RHIC-LHC EraFebruary 21-14, 2008 TIFR

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Motivation

Medium properties Physical phenomenon Experimental probes

Energy density Parton Eloss in the medium High pT particle production, and correlations

Velocity of sound Mach cones 3-particle correlations

Partonic interactions

Mechanism of Eloss

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

Jet-medium coupling

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

Collectivity and Thermalization

Partonic collectivity, viscosity and interactions

Azimuthal anisotropy

Medium effect on particle production mechanism

Parton recombination, modified/vacuum fragmentation

Identified particle correlations

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

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~ˆ

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Current observations in STARAway side yield modification

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

How can we understand these features ?

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Do they give answers to …

Mechanism of energy loss in medium -

Few hard interactions or multiple soft interactions ?What is the Path length dependence of energy loss ? - L2 or LWhat 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

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Di-hadron fragmentation function (Away side)

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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Di-hadron correlations w.r.t reaction plane

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

pTassoc : 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

RMS =i ( i - )2 yi

i yi

RMS

STAR Preliminary

v2{4}

v2{RP}

v2 sys. error

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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

(1-2)/2

(1-2)/2

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

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 ?Can we get an idea about the energy lost by partons in the medium?

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

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

d+AuAu+Au

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Features of the Ridge (at QM2006)

Yield at large independent on

STAR Preliminary

STAR Preliminary

J. Putschke (QM06)

Ridge persists up to high pT-trigTRidge ~ Tinclusive < TjetSTAR : J. Putschke, QM2006

Indication of two contributionsJet contribution + contribution arising due to jet

propagating in the medium

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Jet and Ridge : Observations

Near-side jet yield independent of colliding system, Npart

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

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Particle Ratios: Jet & Ridge

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

Jet : /K0s ~ 0.5 < inclusive

Ridge : /K0s ~ 1 ~ inclusive

Ridge vs. InclusiveJet Cone vs. Inclusive

STAR PreliminarySTAR Preliminary

Jet

ridge

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Theoretical model interpretations

2)Transverse flow boostS.A.Voloshin, Phys.Lett.B. 632(2006)490E.Shuryak, hep-ph:0706.3531

1)In medium radiation + longitudinal flow pushN.Armesto et.al Phys.Rev.Lett.93(2004) 242301

3)Turbulent color fields A.Majumder et.alPhys. Rev. Lett.99(2004)042301

4)Momentum Kick C.Y. Wong hep-ph:0712.3282

5)Recombination between thermal and shower partonsR.C. Hwa & C.B. Chiu Phys. Rev. C 72 (2005) 034903

Can we discriminate betweenthese physics interpretations? 3-particle Correlation in

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Motivation for 3-particle correlation in

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T : Trigger particleA1: First Associated particleA2: Second Associated particle

1) Jet fragmentation in vacuum

STAR TPC acceptance for3-particle correlation in (||<1 and full azimuth)

2) In medium radiated gluons diffused in

3) In medium radiated gluons still collimated

4) Combination between jet fragmentation and diffused gluons

= A1-T = A2-T

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Au+Au and d+Au at sNN = 200 GeV

Trigger : 3<pT<10 GeV/c, ||<1Associated : 1< pT<3 GeV/c, ||<1

Select both associated particles Near Side: || <0.7 Away Side: | - |<0.7

Mixed events to obtain background : (a) Min-bias events with same centrality (b) (primary vertex z) < 1 cm (c) Same magnetic field configuration

Analysis techniques

STAR Preliminary

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3-particle correlation background

Raw Raw Raw signal Raw Bkg Hard-Soft Bkg1 Bkg1

Bkg1 Bkg2

correlated

Soft-Soft

- -

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STAR Preliminary

dAu

AuAu40-80%

AuAu0-12%

2-pa

rtic

le C

orre

latio

n

STAR Preliminary

3-particle correlation (||<0.7)

STAR Preliminary

dAu

AuAu40-80%

AuAu0-12%

3<pTTrig<10 GeV/c

1<pTAsso<3 GeV/c

Shaded : sys. error.

Line :v2 uncer.

STAR Preliminary

dAu

AuAu40-80%

AuAu0-12%

STAR Preliminary

dAu

AuAu40-80%

AuAu0-12%

0.7<R<1.4

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Comparison (Projections)3<pT

Trig<10 GeV/c 1<pT

Asso<3 GeV/c|| <0.7

AuAu 0-12% is higher than dAu and AuAu 40-80%

0.7<R<1.4

STAR Preliminary

STAR Preliminary

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Summarizing … 3-particle correlation in

Ridge is uniform event by event.

3<pTTrig<10 GeV/c,

1<pTAsso<3 GeV/c, ||<0.7

The ridge is approximately uniform or broadly falling with . No significant structures along diagonals or axes.

STAR PreliminarySTAR Preliminary STAR Preliminary

dAu AuAu 40-80% AuAu 0-12%

+ = Jet

Ridge

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Potential for away-side analysis

3<pTTrig<10 GeV/c

1<pTAsso<3 GeV/c

|-| <0.7

Study the ridge with the help ofDi-hardon correlation w.r.t. reactionplane.

Another tool to study Ridge

STAR Preliminary

3<pTtrig<4GeV/c

1.0<pTasso<1.5GeV/c

STAR Preliminary

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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 Particle ratios in ridge similar to inclusive measurements Di-hadron correlations with respect to reaction plane

indicates - ridge is dominated in-plane, consistent with

medium density effect

STAR Preliminary

Jet Cone vs. Bulk

Ridge vs. Bulk

STAR Preliminary

STAR Preliminary

STAR Preliminary

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Summary: Meduim Response

Three-particle correlation in - can potentially identify the underlying physics of the ridge.

Correlation peak at =~0, characteristic of jet fragmentation, is observed in d+Au, Au+Au 40-80% and central Au+Au 0-12%.

The peak sits atop of pedestal in central Au+Au. This pedestal, composed of particle pairs in the ridge, is approximately uniform or broadly falling with in the measured acceptance. No significant structures along diagonals or axes.

Significant step forward in experimental study. Quantitative theoretical calculations are needed for further understanding.

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ThanksThanks to STAR CollaborationArgonne National Laboratory

Institute 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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Back up

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Black : Raw signal

Pink : Mixed-event background

Blue : Scaled bkgd by ZYA1

Red : Raw signal – bkgd

2-particle correlation

AuAu ZDC central (0-12%) triggered data, 3<pT

Trig<10 GeV/c, 1<pTAsso<3 GeV/c

acceptance corrected

STAR Preliminary

||<0.7 ||<0.7

Ridge