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Mapping out the Jet correlation landscape: Perspective from PHENIX

Jiangyong Jia for PHENIX CollaborationStony Brook University & BNL

23th WWND Big Sky, MT February 11-18, 2007

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Trigger and associated pT

Aw

ay jet

I AA

Thermallized gluon radiation

Shock wave or cherenkov? flow, Jet broadening

Punch through jets or tangential contribution?

Correlation landscape in pT1, pT2

T 3T

I II III IV

Rich interactions between jet and medium

Low pT Moderately high pTIntermediate pT high pT

Main goal is to understand: Quenching of the jet by the medium Response of the medium to the jet

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Evolution with pT1,pT2

Away jet shape: broaden shape -> dip -> broaden shape -> peak

Dip grows

Jet emerges

PHENIX Preliminary

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Pt,2

Pt,1

Cone

Flat

peak pt,1 pt,2>4

1<pt,1 pt,2<4

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Pt,2

Pt,1

Cone

Flat

peak pt,1 pt,2>4

1<pt,1 pt,2<4

Competition between “Head” and “shoulder”.

Head region: Suppression of jetShoulder Region: Response of the medium

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Location of the “displaced” peaks

D 1, independent of centrality (at Npart>100), collision system and √s.

D D

Independent of pT (when not dominated by head region)

nucl-ex/0611019

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Relative amplitude of Head/Shoulder: pT dependence

More concave

pT

More concave for increasing pT (in a limited range)

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Relative amplitude of Head/Shoulder: Centrality

dependence

More concave for increasing Npart

More concave

Npart

peripheralcentral

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Broad or displaced peak is seen for different energies.

Relative amplitude of Head/Shoulder: √s dependence

nucl-ex/0611019

More concave

√s =17.2 √s =62.4 √s =200

√s

More concave with increasing √s.

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Relative amplitude of Head/Shoulder: √s dependence

Peak ~ 0.17, Min ~0.07

||<0.35

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Peak ~ 0.07, Min ~0.06CM<0.7

Relative amplitude of Head/Shoulder: √s dependence

Peak ~ 0.17, Min ~0.07

Shoulder200 GeV 2.5x Shoulder17.2 GeV

Head200 GeV Head17.2 GeV ||<0.35

Head: Jet dominate! Jet multiplicity at SPS is lower, but less quenching

Shoulder: Weaker medium response at SPS ?

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A possible picture

Head region: Suppression of jetFragmentation of surviving jet and its radiated gluons

Shoulder Region: Dissipation of the lost energy in mediumCherenkov/Mach Shock/Deflected jet

Increase pt

Cherenkov:wrong pT dependence

Mach Shock + jet

Deflected jet: models need to describe the pT dependence (Hydro wake, Hwa’s MPS model, large angle rad.)

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Chemistry of the Shoulder/Cone?

Triggering on high pT and identify the associated hadrons Cone shape observed for associated baryons, but away side is flatte

r than mesons.

0-20%2.5-4x1.6-2 GeV/c

Baryon/meson increase with pT and centrality Jet frag.<Bayron/meson< bulk medium.

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Chemistry of the Shoulder?

ud

uu

d

uud d

u

uud d

u

Bulk medium are boosted by shock wave, which then coalesce into hadrons? => jet frag.<Bayron/meson<Bulk

Cooper-Fryer

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Quantify the yield: IAA

Integrate the yield in near side: ||</3, away side: ||</2, and make

IAA = YAA/YPP

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IAA = YAA/YPP

Enhancement at low pT,assoc due to “shoulder” Suppression at large pT,assoc due to “head”

Away side

Away side

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IAA = YAA/YPP

Strong modification persists to high pT trigger

Away side

Shoulder enhancement

Head suppression

Away side

Competition between enhancement in the Shoulder region and suppression in the Head region. Jet narrows as function of pT,trig, pT,assoc. The fraction of jet fragmentation and gluon radiation ends up in the “Hea

d” region is larger. Jet (“Head”) spectra in pT,assoc is harder than medium (“Shoulder”), shoulder enhancement limited to 4 GeV/c

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IAA = YAA/YPP

Enhancement at low pT,assoc

Suppression at large pT,assoc

Near side

Near side

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IAA = YAA/YPP

Modifications decrease with increasing trigger pT (flattening)

Near side

Near side

8<pT,t<15GeV/c

zT

STAR

Ridge enhancement

Note: PHENIX ridge yield is smaller than STAR due to smaller range (PHENIX:||<0.35, STAR:||<1)

Modification limited to pT,trig, pT,assoc<4 GeV/c, similar to the range for away side cone.

STAR: This is due to near side ridge

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Near side width

Trigger pT =

2.5-4 x 2-3 GeV/c

Ridge is also reflected in the broadening of the near side width at intermediate pT

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Sources of “jet” pairs One usually find only one “jet” pair per event. “Jet” is statistical sum of different types of signals

Near jet

Ridge

Cone

Away jet

L~0

L<R

L~2R

0 <L<2R

Three particle correlation signal

sum of

Different geometrical bias and trigger bias0

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Sources of “jet” pairs

Near jet

Ridge

Cone

Away jet

L~0

L<R

L~2R

0 <L<2R

Medium response + reco

Jet fragmentation + radiation

0

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Ridge vs cone: different medium response?

Both important up to 4 GeV/c in pT,trig, pT,assoc. Softer than jet. Both have particle composition close to bulk.

Ridge width in is broader than jet, but no displaced peak.

Same origin: due to different <L>? Ridge is a premature cone (T.Renk). Cone also elongated in (T.Renk), but hidden by swing.

Different origin: Away side should also have a ridge, centered around the “Head” region.

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Compare the pT1,pT2, PID, charge, √s dependence of the shape and yield for ridge and cone. If ridge is medium response, it’s charge dependence very different from near side jet. Should have less charge ordering effect. √s can tell us how the medium effect turns on and how it competes with the jet quenching. More quenching->stronger medium response.

Distinguish the ridge and cone

Dial the <L> of near and away side jet with multi-par.corr.(T.Renk) Trig on two back-back high pT particle, and correlate with soft particle?

Note: Possible only if the high pT away side have significant punch-though component

Tangential emission

trig1 trig2

assoc

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Correlation at very low pT

Away “Cone” shape seen for low pt-low pt correlations in central Au+Au (Npart>100) Correlation among soft particles generated or boosted by jets? Why no near side ridge structure?

200 GeV Au+Au, 0-5% Central

PHENIX Preliminary

0.2 < pT,1 < 0.4 GeV/c, 0.2 < pT,2 < 0.4 GeV/c, ||<0.1

Like-Sign Pairs Unlike-Sign

Pairs

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Comments on flow background subtraction

v2{2}, v2{4}, v2{RP}, v2{v1RP} etc. PHENIX use the v2{RP}, where RP determined in 3<||<4 STAR use the average between v2{RP} and v2{4}.

CF = J() + (1+2<v2tv2

a>cos2)

Two-particle correlation automatically includes all non-flow and e-b-e fluctuations. So v2{2} should be used, except that non-flow due to jet need to be removed since it is the signal.

PHENIX v2{RP} is not affected by jet (nucl-ex/0609009). But it measures in fact:2

2 2v v 2

2 22 2 2

2

1 1.063v

v v vv

v2{4} is too small because it removes the ebe eccentricity fluctuations.

(P. Sorensen QM06 talk). STAR use a smaller v2 in bg subtraction than PHENIX

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Backup

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Which v2 should be used?

The non-flow/v2 fluctuation effects (if any) contributes to the flow background. Exception is v2 bias from jets.

CF = J() + (1+2v2tv2

a cos2)

Physical v2 part.

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2

2 22 2 2

2

1 1.063v

v v vv

physics is driven by the ebe rotated RP: v2{2} should be used (modulo removing jet bias).

Which v2 should be used?

Rajeev,Ollitrault, PLB641:260,2006.

v2{EP} does not include v2 fluctuation

systematically too small.

1/ 422 42{4} {4} 2 part partv

22{2} {2} partv

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Non-flow/bias effect due to jets

1) HIJING events are randomly assigned a RP direction and particles are weighted according to the experimental measured v2(pT,)

2) Embed pythia di-jet events (trigger >6 GeV/c) into the HIJING with flow

Jet bias should be small at BBC (3<|<4), we confirm it with simulation

Event

nucl-ex/0609009

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The perturbation in Reaction Plane is correlated with the jet direction. This leads to a fake v2 (non-flow) of the jet at mid-rapidity

This fake v2 depends on the multiplicity and eccentricity.

Large bias

small bias

Distribution of mid-rapidity triggers respective to the RP determined in 0.8<<2.8

Before embedding After embedding

Fake v2 generated!

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Fake v2 of the high pT triggers Note, the true v2 of trigger is

0.

0.42.8

Central Peripheral

1.02.8

3.04.02.02.8

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Jet multiplicity is modified, so we embed pythia doubling the jet multiplicity.