Surface Effects on Jet Production (2+1 correlation study)

STARSTARSurface Effects on Surface Effects on

Jet ProductionJet Production

(2+1 correlation study)(2+1 correlation study)

Olga Barannikovafor the STAR Collaboration

2

16-19 July 2007 Olga Barannikova

University of Illinois at ChicagoEarly Time Dynamics in Heavy Ion Collisions

STARSTAR

OutlineOutline

MotivationEvolution of jet-type correlation analysesTheoretical interpretation of data

Data Analysis Results

Energy loss in di-jet events Summary

3



STARSTAR

Signature two-particle correlation result: Disappearance of the away side jet

in central Au+Au collisions• Evidence for strongly interacting

medium Effect vanishes in peripheral/d+Au

collisions

4<pT trig<6 GeV/c 2<pT assoc<pT trigPRL 91 (2003)

072304

MotivationMotivation

One high-pT, one low-pT trigger Reappearance of the away-side jet Double-hump structure hints at

additional physics phenomena

3<pT trig<4 GeV/c 1.3<pT assoc<1.8M. v Leeuwen,

Hangzhou ‘06

4



STARSTAR

Energy Loss MechanismsEnergy Loss Mechanisms

Jet Quenching Dissipation jet energy when

propagating through the medium

Mach-Cone Could result in double-hump

structure on away-side

Mono-jet Single jet on near-side Excess on away side due to

momentum conservation

“near-side”“away-side”

Courtesy of R .Hollis

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STARSTAR

To address the mechanisms of energy loss in the hot QCD medium

Mach cone (Stoecker, Casalderrey-Solana, Shuryak, Teaney)

Cherenkov gluon radiation (Koch, Majumder, Wang)

Jet quenching & fragmentation (Vitev) Parton multiple scattering (Chiu, Hwa) Color wake (Ruppert, Muller) Flow-induced deflection (Armesto,

Salgado, Wiedemann)

Use di-jets to explore how these effects happen

4<pT trig<6 GeV/c 2<pT assoc<pT trig

PRL 91 (2003) 072304

Phys.Lett. B639 (2006) 38

Energy Loss in QCD MediumEnergy Loss in QCD Medium

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STARSTAR

Two high-pT triggers Reappearance of the

away-side jet• For central Au+Au

collisions

First observation of di-jets

New analysis exploits this observation

PRL 97 (2006) 162301

8<

pT (trig

)<15 G

eV

/c

First Di-Jet ObservationFirst Di-Jet Observation

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STARSTAR

Aim of this analysis is to “pin” the jet axis Assuming di-jets

Only select events with high-pT particles back-to-back in

Correlate all particles with this axis

associates

associates

primary

trigger (T1)“jet-axis”

trigger (T2)

Signal sit atop of a largely

uncorrelated background

Data Analysis - TechniqueData Analysis - Technique

Courtesy of R .Hollis

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STARSTAR

Simulation of one scenario, mach-cone

New method should be sensitive to this and other effects

*by M. Andrews (UIC)

Unmodified Jet*

Simulation

Modified Jet*Simulation

Monte-Carlo Shape ExamplesMonte-Carlo Shape Examples

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STARSTAR

Require that the 2 highest pT particles are back-to-back in

Assume this defines the jet-axis, look in 2D-space about the second trigger

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

Raw, uncorrected signalT1T2

Correlation primary trigger (T1) and “jet-axis trigger” (T2)

Data Analysis – Di-Jet SelectionData Analysis – Di-Jet Selection

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STARSTAR

Accounts for: pair acceptance

• triangular shape in uncorrelated

background• particles not related to

initial jet

Mixed Events Background:Mixed Events Background:

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STARSTAR

Need to account for elliptic flow

Phys.Rev. C72 (2005) 014904

0 - 10% 10-20%

20-30% 30-40%

Note: this is the correction function for T1A1

)2cos(

22sin

21

22sin

221 11

22

12

12

22

12

12

ATTT

ATAT

aa

vv

aa

vvvv

Dynamic weighting in analysis

VV22 Removal:Removal:

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STARSTAR

Normalization:Normalization:

T1T2

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

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STARSTAR

T2A1

Normalization:Normalization:

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

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STARSTAR

2+1 Signal Construction:2+1 Signal Construction:

Raw Correlation Background

Signal

0 - 10% 10-20%

20-30% 30-40%

Flow

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

STAR Preliminary

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STARSTAR

Single trigger

Di-jet trigger

Di-jet trigger no modification on

away-side Surface dominated? No energy loss for di-

jets?

One high-pT trigger (only) away-side

modification Mono-jets? Energy loss for away-

side jet?

T1A1

T2A1_T1

Preliminary Results:Preliminary Results:

STAR Preliminary

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

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STARSTAR

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

Accounting for correlated background on T1 and T2 side

Signal + Background

Background

Signal

T1T2

Correlated Background:Correlated Background:

STAR Preliminary

+ - 2+1 correlation for all qualified T1, T2 pairs

+,+ - Correlated background (approximated by di-hadron T1A1, T2A1 correlations)

+ - Corrected 2+1 signal

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STARSTAR

Correlation of associates with: T1 (also requires a T2) T2

Detailed shape of near- and away-side is the same

T1A1_T2

T2A1_T1

Same-side widths:

Selection Au+Au d+Au

5-4-1.5 0.21±0.04 0.22±0.01

6-4-1.5 0.20±0.03 0.19±0.04

Di-Jets in Au+Au CollisionsDi-Jets in Au+Au Collisions

STAR Preliminary

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

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STARSTAR

projection

projection

No apparent -“ridge”

Shape ModificationsShape Modifications

No shape modification

STAR Preliminary

STAR Preliminary STAR Preliminary

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

J. Putschke, QM2006

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STARSTAR

STAR Preliminary **

Surface EffectsSurface Effects

T1: pT>5GeV/c

T2: pT>4GeV/c

A: pT>1.5GeV/c

If the triggers have tangential bias: expect a term related to the surface

Surface ~ R2 ~ Npart2/3

d+AuSTAR Preliminary **

** Shown are statistical errors only

Number of triggers per event (per number of binary collisions)

Single triggers and (all qualified) pairs behave similar to inclusives

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STARSTAR

Summary:Summary:

New analysis of 2+1 correlations Events triggered with 2 high-pT particles

Preliminary results show a di-jet structure with this technique, with no modification

Surface bias in di-jet emission is likely, new technique allows further exploration

Many thanks to A. Iordanova, R. Hollis, M. Andrews

Documents

Surface Effects on Jet Production (2+1 correlation study)