Understanding Jet quenching and Medium-response via dihadron correlations

1Jiangyong Jia, QM2008, Feb. 8, Jaipur

Understanding Jet quenching and Medium-response via dihadron correlations

Jiangyong Jia Stony Brook University & BNL

Medium

Jet

?

Mostly based on PHENIX paper: nucl-ex/0801.4545

Thanks Fuqiang Wang for inputs


Deer’s antler

Horse’s head

Cow’s hoof

Donkey’s tail

四不像The “four-unlikes”

Pere david’s deer


Jet quenching & medium response

53

RA

A

pT

1

Jet fragmentation

Flow+Recombination

0.2

d+Au Au+Au 0-5%8 < pT(trig) < 15 GeV/cpT(assoc)>6 GeV

Fragmentation of jets with minimal eloss Dissipation of lost energy in medium

Jet + ridgeSuppressed Jet + hump

The mechanisms for single hadron production are important for dihadron and vice versa

*


pT Scan: evolution of jet quenching and medium response

Study the pTa x pT

b dependence of the four components

pTa

pTb

Soft region (medium)

Hard region (jet)

(rad)

Head region (suppressed jet) Shoulder region (hump)

Near region (jet+ridge)


pT Scan: evolution of jet quenching and medium response

Can all the features fit in the four-components picture?

Incr

ease

trig

ger p

TIncrease partner pT

Dip develops

Jet reemerges

Yield enhanced

Yield suppressed


pt,a pt,b>5

Hard region (jet)

1<pt,a pt,a<4

Soft region (medium)

1<pTa,b < 4 -> RHS<1 -> Shoulder region dominant!

pTa or b >5 -> RHS>1 -> Head region dominant!

pTa or b < 1 -> RHS~1

Competition between “Head” (Suppression) and “shoulder” (enhancement)

Shoulder is important up to ~4 GeV/c

Away-side pT ScanRHS = Head_yield/shoulder_yield (area normalized)

pTa

pTb

RHS<1

RHS>1


Near-side pT Scan

For low pT region Au+Au shape in is b

roader than for pp Au+Au yield is enhanc

ed, especially at large .

For high pT region shape/yield is simil

ar between Au+Au and pp

The ridge component is important to ~4 GeV/c

Jet fragmentation takes over at higher pT.


Spectra slope at shoulder region

2<pTa<3

3<pTa<4

4<pTa<5

Mean-pT at intermediate pT (1<pTb< 5)

Shoulder slope ~0.45 GeV/c, independent of trigger pT

arxiv:0705.3238 [nucl-ex] Phys.Rev.C77:011901,2008


Near-side slope

Ridge slope is slightly harder than the shoulder

J. Putschke QM06

John Chen poster

JetRidge

0.44 GeV/c

0.36 GeV/c


Connection between ridge and shoulder

Ridge and shoulder persist up to pTa,pT

b~4 GeV/c They have similar slope (ridge is slightly harder)

0712.3033 nucl-ex

Near-side Away-side

Their particle compositions are similar to bulk. Ridge & Shoulder energies are roughly balanced in a given slice.

Aw

ay_e

nerg

yN

ear_

en

erg

y

0.5<0.7

John Chen poster

0.5<0.7

*


Energy dependence for shoulder & ridge

CM<0.7

Head200 GeV Head17.2 GeV Shoulder200 GeV 2x Shoulder17.2 GeV

Near200 GeV 8 x Near17.2 GeV

||<0.35

At SPS Smaller jet quenching+Stronger Cronin

-> Less suppression in Head Smaller medium component

-> Smaller ridge/ Shoulder

RAA at SPS is totally different, dominated by Cronin effect

Ridge is almost gone at SPS energy, the shoulder due to kT broadening?Energy scan is important!

*


= per-trig yield

Quantify the medium modifications

Pair Yieldper-trig yield=

Trig Yield

per-jet yield

per-trig yield

AA

pp

per-trig yieldI =

per-trig yieldAA

IAA is a good quantity at high pT(per-trigger yield = per-jet yield) but is diluted by soft triggers at low pT.

Both scales with Ncoll

PairYield

PairYieldAA

AAcoll pp

JN

TrigYield

TrigYieldAA

AAcoll pp

RN

( , )( , )

( )

a ba b AA T T

AA T T aAA T

J p pI p p

R p

( , ) ( , )AA AA

a b b aT T T TJ p p J p p

*


Low pT triggerIaa vs pT

Dilution of soft triggers: T-T recombination / triggering on medium response.

Near side

High pT trigger

IAA~1

IAA~ RAAAway side

I AA


Dilution of soft triggers

IAA not symmetric wrt trigger/partner pT selection

Near-side

Since one particle is high pT, hadron pair come from jets emitted near surface The second particle in the pair also comes from surface.

But the low pT triggers in per-trigger yield include all soft hadrons.


Dilution to ridge

scaledscaled

Scale up the Au+Au by 1/IAA(pTa), then subtract pp

Near-side

~consistent with pp jet + roughly flat ridge

*


Another example: Dilution effect in dAu1/

N trig

dN/

d(Δ)

STAR Preliminary

Aud

Large xSmall x

Triggers: ~0, 3 GeV/c partners: ~3, 0.2 GeV/c

g

q

Forward

g

q

Backward

Per-trigger yield

p-p : 1/2

Dilution effect due to trigger counting! Do not need recombination

CGC suppress num. of forward-scattering

Au-side: 1/3d-side: 2/3

Small xLarge x

*

Fuqiang



Geometrical bias?

High pT correlated pairs

Surface emission

Low pT correlated pairs

Bulk emission

Mach cone

ridge

*



Geometrical bias?

High pT correlated pairs

Surface emission

Low pT correlated pairs

Bulk emission

• Low pT triggers may from cone/ridge surface bias reduced!• Each side contain both ridge and cone contributions


Jet contribution @ low pT

Quantify the jet contribution in two-particle momentum spaceHelp understand the particle production mechanism

J AA

pTa,pT

b

1

Medium response increase the pair yield at low pT

PairYield

PairYieldAA

AAcoll pp

JN

53

RA

A

pT

1

Jet fragmentation

Flow+Recombination

0.2

TrigYield

TrigYieldAA

AAcoll pp

RN

*


Near side pair yield modification: JAA

Approximately scales with pTsum=pT

a+pTb (since coming from same jet)

Reach same level (RAA) at High pTb

PairYield

PairYieldAA

AAcoll pp

JN

Pair yield scale faster than Ncoll at low pTa+pT

b

These pairs are remnants of quenched jets.


JAA @ away-side head region Low pT pair yield is not suppressed! Away-side JAA ~ RAA

2 at large pT. away-side jet IAA ~ inclusive jets RAA

J AA(p

Ta ,pTb )


3-p correlation telling the same story?

Au+Au Central 0-12% Triggered

2D

D~1.1 D~1.36

Exclusive process selects verydifferent kinematical region and phase space

*


RP dependence at low pT Rich dependence patterns of medium response on trigger orientation

PHENIX show jet function, need to ~x (1+2v2trigcos2) to compare. V2/V4 systematics are clearly important!! (enter linearly)

3<pTtrig<4GeV/c & 1.0<pT

asso<1.5GeV/c 20-60%STAR

M. McCumber, A.Feng, Session VIII, Feb. 5


Models for medium response Production mechanisms of associated hadrons

New particle creation: feedback of shower gluons, cerenkov gluons

Local heating: bending jet, momentum kick, Mach cone, backsplash, Glasma bending, coupling to transverse or longitudinal flow etc.

Residual correlations with geometry: elliptic flow (subtracted), correlation between radial flow boosted beam and surfaced emitted transverse jet.

Easier to generate large yield by pickup from the bulk (since no particle production is required)

We know the pair yield is enhanced at low pt. Supported by the property of the ridge/cone (PID, slope etc)

Mechanisms for ridge and shoulder may well be related.

*


Final remarks: Jet quenching & medium response

Jet @ High pT, surface biased, eloss mechanism is constrained indirectly from those with little eloss

Medium response @ Low pT, no surface bias, directly sensitive to energy loss process.

The energy loss mechanism affects characteristics of medium response, example:

collisional/radiative <-> momentum kick/gluon feedback. Different medium response mechanism may require diffe

rent energy loss scenario. Energy loss and energy dissipation to the medium

are modeled separately. But there shouldn’t be a strict separation of scale, especially for intermediate pT.

Need a unified framework that include both jet quenching & medium response, and can describe correlation data at all pT.

More details:M. McCumber, Session VIII, Feb. 5H.Pei, A.Adare, SessionIX, Feb.8

Poster 23,24


Backup


Constraining the eloss dynamics

Shift to left

Case I

pT

Yield p+p

A+A

AbsorptionDownward shift

Case II

Absorption Longer path for away-side jet, IAA<RAA Independent of spectra shape

Left shift Stronger energy loss, IAA>RAA Flatter away-side spectra IAA<RAA

Data suggests IAA ~ RAA Flatter spectra compensated by bigger energy

loss By combing IAA and RAA, one gain some

sensitivity on energy loss.

dn/dpt ~(1/pt)9 for single spectra

dn/dpt ~(1/pt)5 for away-side spectra

8.1 2

1( )1 ( ) 0.23T

AA TT

E pR p

p

4.8 1

1( )1 ( ) 0.35T

AA TT

E pI p

p

50% bigger

nucl-ex/0703047


d+Au Au+Au 0-5%

Per

-trig

ger

yiel

d

8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV

High pT: jet fragmentation

Observed jet are those “do not” suffer much energy loss.

Near-side: surface emission Away-side: tangential/punch-through emission.

Iaa~Raa, consistent with energy loss calculation

H. Zhang, J.F. Owens, E. Wang and

X.-N. Wang , PRL 98(2007)212301


Low pT: medium response to jet Away-side: strongly modified shape and yield

Suppressed jet (head region) + medium-induced component (Shoulder region)

Near-side: elongated structure in , enhancement in yield. Surface Jet + medium-induced component (ridge)

STAR

(rad)

Documents

Understanding Jet quenching and Medium-response via dihadron correlations