Star results on medium properties and response of the medium to energetic partons
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STAR results on Medium Properties and Response of the Medium to Energetic Partons. Bedanga Mohanty (For the STAR Collaboration) Variable Energy Cyclotron Centre, Kolkata. Outline. Motivation Parton Energy Loss Medium Response to Energetic Partons Summary. Motivation.

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

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Star results on medium properties and response of the medium to energetic partons

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

Bedanga Mohanty

(For the STAR Collaboration)

Variable Energy Cyclotron Centre, Kolkata

Outline

  • Motivation

  • Parton Energy Loss

  • Medium Response to Energetic Partons

  • Summary


Motivation

Motivation

Correlations play a significant role in understanding medium properties


Basic approach

Leading/trigger particle

Near side

Associated particles

Dj

Absence of

medium

STAR Preliminary

Away

side

New STAR high pT p+p results

away

near

Basic Approach

Calibrated probe

Look for modification

Medium formed in

heavy-ion collisions

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

Jet and high pT particle production

in pp understood in pQCD framework

STAR : PRL 97 (2006) 252001

STAR : PLB 637 (2006) 161

Is there any modification in heavy ion collisions ?


Advantage of di hadron correlations

Di-hadron

Single

y (fm)

y (fm)

x (fm)

x (fm)

Less surface bias

Limited sensitivity of RAA to P(E,E)

T. Renk, PRC 74 (2006) 034906

T. Renk and Eskola,hep-ph/0610059

2IAA

2RAA

Di-hadron correlations more robust

probes of initial density ~

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

Advantage of Di-hadron Correlations


Current observations in star

Enhanced correlated yield

at large  on near side

Away side shape modification

2.5 < pTtrig< 4 GeV/c

1< pTassoc < 2.5 GeV/c

d+Au

Au+Au

Medium response

STAR: PRL 95 (2005) 152301

J.G. Ulery, QM 2005

STAR : J. Putschke, QM2006

STAR : M. J. Horner, QM2006

pTtrig=3-6 GeV/c,

2 GeV/c <pTassoc< pTtrig

Reappearance of di-jets

STAR : PRL 97 (2006) 162301

Current Observations in STAR

High pT suppression

Away side yield modification

Parton Eloss

pTlp : 4 - 6 GeV/c

STAR : PLB 655 (2007) 104

STAR : PRL 97 (2006) 152301

STAR : PRL 91 (2003) 072304

pTasoc : 2 GeV/c - pTlp

What does these features reveal about the medium ?


Do they give answers to

Mechanism of energy loss in medium -

What is the Path length dependence of energy loss ? - L2 or L

Do 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?

Do they give answers to …

Few hard interactions or multiple soft interactions ?

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


Results on partonic e loss

Results on Partonic Eloss

Parton Eloss

Medium response

Reappearance of di-jets

Results to be discussed in this talk :

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)


Is there a difference in q g e loss

Anti-particle to particle ratio

Baryon & meson NMF

STAR Preliminary

STAR Preliminary

Eg

~ 9/4

X.-N. Wang,

PRC 70 (2004) 031901

Eq

2

D

E

<q>

^

L

a

C

s

Anti-Baryon to meson ratio

STAR Preliminary

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

Patricia Fachini, Parallel Talk, 5th February

STAR : PLB 637 (2006) 161

STAR : PRL 97 (2006) 152301

STAR : PLB 655 (2007) 104


Away side di hadron fragmentation function

6< pT trig < 10 GeV

IAA

STAR Preliminary

Npart

  • Inconsistent with PQM calculations

  • Modified fragmentation model better

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

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

Away-side Di-hadron Fragmentation Function

zT=pTassoc/pTtrig

1/Ntrig dN/dzT

STAR Preliminary

STAR Preliminary

IAA

zT

  • Denser medium in central Au+Au

    collisions compared to central Cu+Cu

  • zT distributions similar for Au+Au

    and Cu+Cu for similar Npart

Oana Catu, Parallel Talk, 8th February


Di hadron correlations w r t reaction plane

trigger

in-plane

trigger

out-of-plane

Observations :

  • 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

Di-hadron Correlations w.r.t Reaction Plane

in-plane fS=0

3< pTtrig < 4 GeV/c,

pTasso : 1.0- 1.5 GeV/c

out-of-plane fS=90o

20-60%

STAR Preliminary

Au+Au 200 GeV

top 5%

STAR Preliminary

d+Au

Aoqi Feng, Parallel Talk, 5th February


Path length effects

i ( i - )2 yi

RMS =

i yi

RMS

Path Length Effects

STAR Preliminary

v2 sys. error

v2{RP}

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.

v2{4}

Au+Au 200 GeV

3< pTtrig < 4 GeV/c

1.0 < pTasso < 1.5 GeV/c

Away-side features reveal path length effects

Aoqi Feng, Parallel Talk, 5th February


E loss probability distribution hadron correlation

Jet

X.-N. Wang et al

PRL 77(1996)231

  • 1st measurement of away-side

    -h correlations

  • Suppression similar level as

    inclusives in central collisions

    Note : Ejet = E

Promptg

A. Hamed (Parallel Talk on 8th Feb)

Eloss probability distribution : -hadron correlation

  • Provides constraints on Eloss

    probability distributions

  • Possibly gives full accounting

    of jet energy loss

T. Renk : PRC 74 (2006) 034906


Results on medium response

Results on Medium Response

Parton Eloss

Reappearance of di-jets

Medium 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)


Conical emission

STAR Preliminary

near

near

dAu

e-h correlation

STAR Preliminary

STAR Preliminary

Medium

Medium

away

away

Conical emission or deflected jets ?

(1-2)/2

deflected jets

(1-2)/2

Central Au+Au 0-12%

Conical Emission

Conical Emission

Experimental evidence of Conical emission

3 <pT-trig < 4 GeV/c

1 < pT-assoc < 2 GeV/c

  • Two component approach

  • Correlated to trigger (jets..)

  • Uncorrelated to trigger

  • (except via anisotropic flow)

  • Bkg normalization 3-particle ZYAM

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

Gang Wang (Parallel Talk on 8th Feb


Mach cone or cerenkov gluons

C3



STAR Preliminary



Subtraction of v2v2v4 terms

using on v2 = 0.06

Subtraction of v2v2v4 term

using v2 = 0.12

Strength and shape of away side structures

observed depends on assumed magnitude of flow

coefficients

In cumulant approach: no conclusive evidence

for conical emission so far

Claude Pruneau : STAR : QM2008(Poster),

PRC 74 (2006) 064910

Mach Cone or Cerenkov Gluons

Cone angle (radians)

  • Mach-cone:

    Angle independent of associated pT

  • Cerenkov gluon radiation:

    Decreasing angle with associated pT

STAR Preliminary

pT(GeV/c)

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


Ridge in heavy ion collisions

d+Au, 40-100%

Au+Au, 0-5%

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

Ridge in Heavy Ion Collisions

Au+Au

d+Au

What does these features reveal about the medium ?

Perhaps tells us how the energy lost by partons are distributed

in the medium


Features of the ridge at qm2006

STAR Preliminary

Ridge persists up to high pT-trig

TRidge ~ Tinclusive < Tjet

Indication of two contributions

Jet contribution + contribution arising due to jet

Propagating in the medium

STAR Preliminary

What could be the different physics possibilities ?

Features of the Ridge (at QM2006)

STAR Preliminary

Yield at large  independent on 

STAR : J. Putschke, QM2006


Different physics possibilities

Different Physics Possibilities

QCD bremsstrahlung radiation boosted

by transverse flow

S.A.Voloshin, Phys.Lett.B. 632(2007)490

E.Shuryak, hep-ph:0706.3531

In medium radiation and longitudinal flow push

N.Armesto et.al Phys.Rev.Lett.

93(2007) 242301

Broadening of quenched jets in turbulent color fields

A.Majumder et.al

Phys. Rev. Lett.99(2004)042301

Recombination between thermal and shower partons at intermediate pT

R.C. Hwa & C.B. Chiu

Phys. Rev. C 72 (2005) 034903

Momentum Kick Model

C.Y. Wong hep-ph:0712.3282

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


Jet and ridge observations

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 medium

  • Ridge yield increases with Npart

Oana Catu, Parallel Talk, 8th February

Christine Nattrass, Parallel Talk, 8th February


Particle ratios and v 2 jet ridge

Jet

ridge

v2 modulated background + ridge + jet

  • inferred v2 of events with ridge pair ~ inclusive

  • inferred v2 of events with jet pair < inclusive

Particle Ratios and v2 : Jet & Ridge

Jet Cone vs. Inclusive

Ridge vs. Inclusive

STAR Preliminary

STAR Preliminary

Jet : /K0s ~ 0.5 < inclusive

Ridge : /K0s ~ 1 ~ inclusive

  • Ratios in cone smaller than inclusive

  • Ratios in ridge similar to inclusive

Cristina Suarez - Poster,

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

Jiaxu Zuo - Poster


Ridge di hadron correlation w r t rp

jet

ridge

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

STAR Preliminary

Au+Au 200 GeV

20-60%

Observations :

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

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

3< pTtrig < 4 GeV/c,

pTasso : 1.0- 1.5 GeV/c

Interpretation :

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


Ridge 3 particle correlation

dAu : Jets

AuAu : 200 GeV

STAR Preliminary

3<pTTrig<10 1<pTAsso<3 ||<0.7

Uniform overall excess of associated particles not due to correlated emission

=

+

Ridge : 3-particle Correlation

Jets

In-medium radiated

gluons diffused in

In-medium radiated

gluons still collimated

Jet fragmentation and

diffused gluons

Pawan K. Netrakanti, Plenary Talk, 5th February


Outlook di jets and jet reconstruction

Outlook : Di-Jets and Jet Reconstruction

Parton Eloss

Reappearance of di-jets

Medium 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


Di jets triggered correlations

T1: pT>5GeV/c

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

What happens to these

features if we trigger

on di-jets ?

A1

T1

T2

Di-jet trigger

Di-Jets Triggered Correlations

Observation of di-jets


Di jets triggered correlations1

200 GeV Au+Au, 12% central

1 _dN_

Ntrigd(Df )

4

T2A1_T1

T2A1

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

200 GeV Au+Au & d+Au

2

1 _dN_

Ntrigd(Df )

STAR Preliminary

Au+Au

d+Au

3

0

STAR Preliminary

2

-2

1

1 _dN_

Ntrigd(Dh )

1 _dN_

Ntrigd(Df )

T2A1_T1

T2A1_T1

T1A1_T2

Au+Au

12% central

|Df |<0.7

12% Central

40-60% MB

60-80% MB

0

2

-2

-2

-1

-1

2

0

0

1

1

3

3

4

4

5

5

0

STAR Preliminary

STAR Preliminary

Df

-1

-1.5

0.5

0

-0.5

1.5

1

Df

Df

Dh

Di-Jets Triggered Correlations

No Away-side suppression, No Shape modification, no ridge

Olga Barannikova, Parallel Talk, 8th February


Multi hadron cluster triggered correlations

R

Seed

Associated track

Secondary Seeds

Multi-hadron Cluster Triggered Correlations

Motivation:

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

Away-side spectrum

0-12% Au+Au

Add 12-15 GeV trigger

Multi-hadron trigger

STAR Preliminary

Use cluster energy for trigger:

- R = 0.3

- pT,seed > 5 GeV

- pT,sec seed > 3 GeV

Single-hadron and multi-hadron triggers give similar result

Re-confirms single high pT triggered correlation results

probes jet-like correlations

Brooke Haag - Poster


Summary parton e loss

  • 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 collisions

  • Cu+Cu and Au+Au : zT distributions similar for collisions

    with similar Npart- feature not consistent with PQM

    calculations

  • Path 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

Summary : Parton Eloss

STAR Preliminary

STAR Preliminary


Summary medium response

Summary : Medium Response

  • Strong 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

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

  • excess of associated particles not due to correlated emission

STAR Preliminary

Ridge vs. Bulk

STAR Preliminary

Jet Cone vs. Bulk

STAR Preliminary

AuAu

STAR Preliminary

dAu

STAR Preliminary

STAR Preliminary


Thanks

Thanks

Thanks to STAR Collaboration

Argonne National Laboratory

Moscow Engineering Physics Institute

Institute of High Energy Physics - Beijing

City College of New York

University of Birmingham

NIKHEF and Utrecht University

Brookhaven National Laboratory

University of California, Berkeley

Ohio State University

Panjab University

University of California - Davis

Pennsylvania State University

University of California - Los Angeles

Institute of High Energy Physics - Protvino

Universidade Estadual de Campinas

Purdue University

Carnegie Mellon University

University of Illinois at Chicago

Pusan National University

University of Rajasthan

Creighton University

Rice University

Nuclear Physics Inst., Academy of Sciences

Instituto de Fisica da Universidade de Sao Paulo

Laboratory of High Energy Physics - Dubna

University of Science and Technology of China

Particle Physics Laboratory - Dubna

Shanghai Institue of Applied Physics

Institute of Physics. Bhubaneswar

SUBATECH

Indian Institute of Technology. Mumbai

Texas A&M University

Indiana University Cyclotron Facility

University of Texas - Austin

Institut Pluridisciplinaire Hubert Curien

Tsinghua University

University of Jammu

Valparaiso University

Variable Energy Cyclotron Centre. Kolkata

Kent State University

Wayne State University

University of Kentucky

Institute of Modern Physics, Lanzhou

Warsaw University of Technology

Lawrence Berkeley National Laboratory

University of Washington

Massachusetts Institute of Technology

Institute of Particle Physics

Yale University

Max-Planck-Institut fuer Physics

Michigan State University

University of Zagreb


Color factors and q g e loss

Eg

~ 9/4

Eq

2

D

E

<q>

^

L

a

C

s

Color Factors and q,g Eloss

QCD : For SU(3) : Nc = 3

CA = 3 (gluons), CF = 4/3 (quarks)

S = 0.119

ALEPH : ZPC 76 (1997) 1

OPAL :EJPC 20 (2001) 601

SU(3) is the gauge group for QCD

i,j represent fermion field indices

and a,b gauge field indices

An opportunity to relate experimental observable (of Eloss) to

basic ingredient of QCD - Gauge Group through Color Factors


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