Probe the QGP via dihadron correlations: Jet quenching and Medium-response

1Jiangyong Jia, ISMD Aug 4-9 2007

Probe the QGP via dihadron correlations: Jet quenching and Medium-response

Jiangyong Jia Stony Brook University

Medium

Jet

?


Particle production mechanisms

53

RAA=A+A/p+p

pT

1

Jet

Flow+Recombination

Production mechanisms Jet fragmentation (>5 GeV/c) and Flow+Recombination

0.2

High pT: surface emission

factor of 5


Particle production mechanisms

53

RAA=A+A/p+p

pT

1

Jet

Flow+Recombination

Production mechanisms Jet fragmentation (>5 GeV/c) and Flow+Recombination

0.2

High pT: surface emission Low pT: bulk emissionLocally thermalized QGP -> flow -> recombination

TTthermal+m<v>2

factor of 5


Jet contribution via dihadron correlation

53

RAA=A+A/p+p

pT

1

Jet

Flow+Recombination

0.2

High pT: Jet quenching and Jet tomography. Low pT: Dissipation of lost energy to medium

How the energy of the 80% jet redistributed to low pT? pT scan: Evolution of jet fragmentation and medium

response


Azimuth correlation at high pT

d+Au Au+Au 0-5%

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

Per

-trig

ger

yiel

d

Observed jet are those “do not” suffer energy loss. Near-side: surface emission Away-side: tangential emission

(factor of 5 suppression)


Azimuth correlation at high pT

d+Au Au+Au 0-5%

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

Per

-trig

ger

yiel

d

Observed jet are those “do not” suffer energy loss. Near-side: surface emission Away-side: tangential emission

(factor of 5 suppression)

IAA 0.2 RAA, Why??

STAR, Phys. Rev. Lett. 97 (2006) 162301

I AA

0.2

Direct proof that high pT hadrons are from vacuum fragmentation.

But they do not directly constrains the energy loss processes. Calculations model dependent:

qhat 1~10 GeV2/fm


Average energy loss vs. absorption?

pT

Yield

RAA alone can’t distinguish the two cases. But,

Case I: Suppression factor depends on the spectra shape, Flatter spectra -> larger shift.

Case II: Suppression factor almost independent of the spectra shape

Shift to left

0( )E E

Case I

p+p

A+A

AbsorptionDownward shift

Case II

(1 ) ( ) ( )A E A E E


PRC.71:034909,2005

Due to longer pathlength for away-side jet, it always leads to IAA<RAA. Need shift term!

Consider only absorption term

pT

Yield


Single spectra n= 8.1 in dn/ptdpt

n=4.8 in dn/dpt for 5-10 GeV/c trigger

Per-trigger spectra

Consider only Energy shift

Away spectra flatter than single spectra


2( )

( ) 1n

TAA T

T

E pR p

p

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

• Flatter spectra and longer pathlength) compensated by bigger fractional energy loss --> IAA ~ RAA

• For -jet, pure absorption: IAA=RAA pure energy shift: IAA>RAA.• By combing IAA and RAA, one gain some sensitivity on energy loss

nucl-ex/0410003

50% bigger

Consider only Energy shift

Single spectra n= 8.1 in dn/ptdpt

n=4.8 in dn/dpt for 5-10 GeV/c trigger

Per-trigger spectra

Away spectra flatter than single spectra


Low pT: medium response to jet Near-side: elongated structure in , enhancement in yield.

Jet + medium-induced component (ridge) Away-side: strongly modified shape and yield

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

STAR PHENIX


Away-side particle composition

Similar shape for asso Baryon and asso Meson

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

Jet frag.<Bayron/meson< bulk medium.

W.Holtzmann

Recombine into correlated pairs?


Away-side energy dependence

p+p

CM<0.7

Same pT cut, similar window

Head200 GeV Head17.2 GeV Shoulder200 GeV 2.5x Shoulder17.2 GeV

At SPS Smaller jet quenching -> Less suppressed Head Smaller medium component -> Smaller Shoulder

||<0.35


pT Scan: Competition between Jet and medium

Suppression in HR, enhancement in SR. Jet shape become similar between pp and AuAu at high pT.

Dip grows

Jet emerges

arXiv:0705.3238 [nucl-ex]


Head region: Upper limit of jet fragmentationShoulder Region: Response of the medium

pTA

pTB

Many possible routes! A single number summarizing the shape:

RHS

Dip: RHS<1; Peak: RHS>1; flat: RHS=1

Away-side modification pattern vs pT

jet

medium


Cone

Flat

Peak

1<pTA,B < 4 -> RHS<1 -> Shoulder region dominant!

pTA or B >5 -> RHS>1 -> Head region dominant!

pTA or B < 1 -> RHS~1


pt,1 pt,2>5

1<pt,1 pt,2<4

Competition between “Head” and “shoulder”.Suppression and enhancement

pT Scan: Competition between Jet and medium


Jet spectra slope at low pT

Near-side: flat with Npart (>100), increase with pTA.

Dominated by jet fragmentation


2<pTA<3

3<pTA<4

4<pTA<5

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

Shoulder region: flat with Npart (>100), independent of pTA !

Dominated by medium. Universal slope ~0.44 GeV/c, reflects property of the medium?


Low trigger pT, decrease with Npart Onset of jet quenching, soft contribution dominates (feed in from shoulder)

High trigger pT, flat with Npart Soft contribution dies out, Jet dominate.

STAR Preliminary

||<0.4

dn/d

Fuqiang

Jet spectra slope at head region

Jet and medium dominates different pT


Parton-medium interaction

1) Radiative energy loss -> High pT suppression

Collective mode

Deflected jet

Punch-through jet

Large angle radiation/Cerenkov

Propagation mode

2) Radiated energy converted into flow -> Low pT enhancement

4) Or propagating partons get deflected

3) Radiated energy propagate -> Gluon feedback at low pT


Radiation contribution

A. Polosa, C. Salgado, hep-ph/0607295, sudokov splitting

C. Salgado, U. Wiedemann, hep-ph/0310079

I. Vitev, gluon feedback

Can be large angle => But for hard jets, radiation almost collinear

Can explain multiplicity


Modifications decrease with increasing trigger pT (flattening) Modification limited to pT

A,B 4 GeV/c, similar to the away-side Shoulder.

STAR: This is due to the Ridge.

Near-side yield modification: IAA

Jet

Ridge

Dilution effects due to soft triggers

J. Putschke


Low pT : dilution effect

per-jet yield IAA at low pT is complicated sinc

e the trigger jet is modified.

per-trig yield

IAA reflects modification on Pairs √ and Triggers x

JetPairsper-trig yield=

TrigsAA

pp

per-trig yieldI =

per-trig yieldAA

Jetpairs

Jetpairs AA AA AA AA

A A B BAAAA

coll pp

J R I R IN

AAAA

AA

JI

R

We define pair suppression JAA


Are low pT particles from jets? Near-side jet pairs with one particle in 5-10 GeV/c.

Most of these pairs comes from jet fragmentation. When normalized by 5-10 GeV/c trigger, Iaa ~1. But when normalized by low pT triggers, Iaa <1.

Origins:1) low pT triggers from soft processes such as Thermal-T recombination.2) low pT triggers are jet-induced but don’t have high pT partners:

fragmentation of radiated partons


Near side JAA

At high pT, both hadrons comes from same jet! JAA represent the suppression on the jet (>pt1+pt2). Since Jet suppression is constant at h

igh pT, JAA should approach the constant RAA level at high pT! Low pT Jaa is factor of 4-5 of the high pT limit? (almost no suppression)

These pairs are remnants of quenched jets (not from surface!)

Leading hadron suppressionJet pair suppression

=


Both important at pT<4, softer than jet, similar PID chemistry (see Jana, Anne’s talk).

Mechanisms for Ridge and cone should play a role on both sides. They do not suffer surface bias.

Ridge

Cone

Near jet

Away jet

0

Sources of pairs• Fragmentation contribution from survived jets• Medium-induced contribution from quenched jets

high pT pairs are rare

Connection between Ridge and Cone


Summary

Jet correlation @ high pT provide constraints on the jet quenching and geometrical bias

Jet correlation @ low pT shows complex evolution due to competition between Jet quenching and medium response on both near- and away-side.

Models should describe the full pT dependence (shape and yield).


Backup


ud

uu

d

uud d

u

uud d

u

Medium are boosted by shock wave, which then recombine into hadrons? => jet frag<Bayron/meson

Cooper-Fryer

Recombination is important


Outline

Single particle production mechanisms

High pT: jet fragmentation and surface bias.

Low pT: medium response Away-side properties. Away-side Jet and medium competition Near-side properties. Near-side Pair suppression Connection between near- and away-side medium respo

nse Summary


Should I worry about non-flow in correlation?

PHENIX: event plane measured at 3<|<4, tracks in ||<0.35Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets

•HIJING event is weighed with measured v2(pt,,b)•PYTHIA has 10 GeV dijet•Dijet->Biased Event plane->Fake v2 for trigger of the embedded jets. •Use away-side pp jet to approximate the ridge

Near jet

Away jetΦ

η

Ridge

Hijing+flow


Should I worry about non-flow in correlation?

PHENIX: event plane measured at 3<|<4, tracks in ||<0.35Embed PYTHIA dijet into HIJING event to estimate the non-flow due to jets

•HIJING event is weighed with measured v2(pt,,b)•PYTHIA has 10 GeV dijet•Dijet->Biased Event plane->Fake v2 for trigger of the embedded jets. •Use away-side pp jet to approximate the ridge

3.04.00.42.8Fake v2

nucl-ex/0609009

Near jet

Away jetΦ

η

Ridge

Hijing+flow


What v2 to use in correlation?

C() = (1+2<v2tv2

a>cos2) + J()

Non-flow due to jet is small with BBC Event plane

Other Non-flow and v2 fluctuations contribute to C(), so should be included in the two source model.

If minijets are important, then it should be much longer range in , or many minijets emitted in a correlated way?

Documents

Probe the QGP via dihadron correlations: Jet quenching and Medium-response