High Momentum probesHigh Momentum probes

Nuclear SuppressionNuclear Suppression

CorrelationsCorrelations

Identified particle measurementsIdentified particle measurements

(for theory see lecture 5)(for theory see lecture 5)

hadrons

hadrons

leading particle

Jet: A localized collection of hadrons which come from a fragmenting parton

Parton Distribution Functions

Hard-scattering cross-section

Fragmentation Function

a

b

c

dParton Distribution FunctionsHard-scattering cross-sectionFragmentation Function

c

chbbaa

abcdba

T

hpp

z

Dcdab

td

dQxfQxfdxdxK

pdyd

d

0

/222

)(ˆ

),(),(

High pT (> 2.0 GeV/c) hadron production in pp collisions:

~

Hadronization in QCD (the factorization theorem)

“Collinear factorization”

High-energy parton loses energy by

rescattering in dense, hot medium.q

q

“Jet quenching” = parton energy loss

Described in QCD as medium effect on parton fragmentation:

Medium modifies perturbative fragmentation before final hadronization in vacuo. Roughly equivalent to an effective shift in z:

2 (med) 2 2

1 /( , ) ( , ) ,p h p h p h

E E

zD z Q D z Q D Q

Important for controlled theoretical treatment in pQCD:

Medium effect on fragmentation process must be in perturbative q2 domain.

Induced Gluon Radiation

Induced Gluon Radiation ~collinear gluons in cone “Softened” fragmentation

in je

i j t

t

n e

: increases

z : decreases

chn

Modification according to Gyulassy et al. (nucl-th/0302077) attributable to radiative rather than collisional energy loss

Modification of fragmentation functions (hep-ph/0005044)

STAR, nucl-ex/0305015

energyloss

pQCD + Shadowing + Cronin

pQCD + Shadowing + Cronin + Energy Loss

RAA and high-pT suppression

Deduced initial gluon density at = 0.2 fm/c dNglue/dy ≈ 800-1200

≈ 15 GeV/fm3, eloss = 15*cold nuclear matter (compared to HERMES eA) (e.g. X.N. Wang nucl-th/0307036)

Jet quenching I: hadrons are suppressed, photons are not

FA - QM`04 Strangeness Report 8

nucl-ex/0504001

Energy dependence of RAA

RAA at 4 GeV: smooth evolution with √sNN

Agrees with energy loss models

Two possible mechanisms of radiative e-loss plus collisional e-loss

High energy limit: energy loss by gluon radiation. Two limits:

(a) Thin medium: virtuality q2 controlled by initial hard scattering (LQS, GLV)

(b) Thick medium: virtuality q2 controlled by rescattering in medium (BDMPS)

Trigger on leading hadron (e.g. in RAA) favors case (a).

Low to medium jet energies: Collisional energy loss is competitive!

Especially when the parent parton is a heavy quark (c or b).

q

q

L

q q

g

L

Radiative energy loss in QCD

CS

coherent

LPM Nq

dzd

dI

ldzd

dI ˆHeitlerBethe

2ˆ~ˆ~ LqLqdzd

dIddzE SCS

LPML

med

C

cformation Lt

BDMPS approximation: multiple soft collisions in a medium of static color charges

E independent of parton energy (finite kinematics E~log(E))E L2 due to interference effects (expanding medium E~L)

Medium-induced gluon radiation spectrum:

Total medium-induced energy loss:

2

2

22ˆ

qd

dqqdq mediumTransport coefficient:

Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000)

Extracting qhat from hadron suppression data

RAA: qhat~5-15 GeV2/fm

What does qhat measure?q̂

LqxxGN

Nq medium

C

CS ˆ,1

4ˆ

2

2

Equilibrated gluon gas:number density ~T3

energy density ~T4

43

ˆ cq

qhat+modelling energy density

• pQCD result: c~2 (S? quark dof? …)• sQGP (multiplicities+hydro): c~10

R. Baier, Nucl Phys A715, 209c

Hadronic matter

QGP

~RHIC data

Model uncertainties

q-hat at RHIC

Pion gas

QGP

Cold nuclear matter

sQGP? ??

RHIC data

EASW BDMPS sCR

4ˆ q L2

ˆ q 2

L2d

0

L

ˆ q () 2 ˆ q 00

L

/log

1

4

92

3

ELdy

dN

R

C

Eg

Rs

GLV

BDMPS(ASW) vs. GLVBaier, Dokshitzer, Mueller, Peigne, Schiff, Armesto, Salgado, Wiedemann, Gyulassy, Levai, Vitev

1800dy

dN g

ˆ q 10GeV 2

fm

Rough correspondence: (Wiedemann, HP2006) 900

dy

dN g

fm

GeVq

2

5ˆ

BDMPS

GLV

Medium-induced radiation spectrum

Salgado and Wiedemann PRD68 (2003) 014008

2ˆLqC

30-50 x cold matter density

What do we learn from RAA?

~15 GeV

E=15 GeV

Energy loss distributions very different for BDMPS and GLV formalisms

But RAA similar!

Renk, Eskola, hep-ph/0610059

Wicks et al, nucl-th/0512076v2

BDMPS formalismGLV formalism

Need more differential probes

RAA for 0: medium density I

C. Loizideshep-ph/0608133v2

I. Vitev

W. HorowitzUse RAA to extract medium density:

I. Vitev: 1000 < dNg/dy < 2000

W. Horowitz: 600 < dNg/dy < 1600

C. Loizides: 6 < < 24 GeV2/fmq̂

Statistical analysis to make optimal use of dataCaveat: RAA folds geometry, energy loss and fragmentation

Application to Heavy Ion Collisions: Initial Results

Strong suppression in Au+Au collisions, no suppresion in d+Au:Strong suppression in Au+Au collisions, no suppresion in d+Au:Effect is due to interactions between the probe and the mediumEffect is due to interactions between the probe and the medium

Established use as a probe of the density of the mediumEstablished use as a probe of the density of the mediumConclusion (at the time): medium is dense (50-100x nuclear matter density) Conclusion (at the time): medium is dense (50-100x nuclear matter density)

PHENIX: Phys. Rev. Lett. 91 (2003) 072301

STAR: Phys. Rev. Lett. 91 (2003) 072304

PHOBOS: Phys. Rev. Lett. 91 (2003) 072302

BRAHMS: Phys. Rev. Lett. 91 (2003) 072303ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Binary collision scaling p+p reference

Central RAA Data

Increasing density

The Limitations of RAA: “Fragility”

Surface bias leads effectively to saturation of RSurface bias leads effectively to saturation of RAAAA with density with density

Challenge: Increase sensitivity to the density of the mediumChallenge: Increase sensitivity to the density of the medium

K.J. Eskola, H. Honkanken, C.A. Salgado, U.A. Wiedemann, Nucl. Phys. A747 (2005) 511

A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38(2005) 461

What can we learn about Energy Loss?

Fractional effective energy loss: Sloss (MJT)

“Effective” because of surface bias when analyzing single particle spectra

PHENIX 0 SpectrumRenk and Eskola, hep-ph/0610059

8 < pT < 15 GeV/c

PHENIX, nucl-ex/0611007

Calibrated Interaction? Grey Probes

Problem: interaction with Problem: interaction with the medium so strong that the medium so strong that information lost: “Black”information lost: “Black”

Significant differences Significant differences between predicted Rbetween predicted RAAAA, ,

depending on the probedepending on the probe Experimental possibility: Experimental possibility:

recover sensitivity to the recover sensitivity to the properties of the medium properties of the medium by varying the probeby varying the probe

Wicks et al, nucl-ex/0512076

Interpreting Correlations

Geometric biases:Geometric biases:Hadrons: surfaceHadrons: surface

Di-hadrons: tangential, but depending on Eloss can probe deeplyDi-hadrons: tangential, but depending on Eloss can probe deeply

Charm-hadron, and especially Beauty-hadron(B): depends on ElossCharm-hadron, and especially Beauty-hadron(B): depends on Eloss

Note: b and c produced in pairs, B and C decay into multiple hadrons Note: b and c produced in pairs, B and C decay into multiple hadrons

Gamma-hadrons: Precise kinematics, back to surfaceGamma-hadrons: Precise kinematics, back to surface

Beyond reaction of probe to medium, also reaction of medium to probeBeyond reaction of probe to medium, also reaction of medium to probe

T. Renk, nucl-ex/0602045

pedestal and flow subtracted

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

Di-Jets through Hadron-Hadron Correlations

““Disappearance of away-side jet” in central Au+Au Disappearance of away-side jet” in central Au+Au collisionscollisions

0-5%

Escaping Jet“Near Side”

Lost Jet“Far Side”

STAR, PRL 90 (2003) 082302

IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)

Evolution of Jet Structure

At higher trigger pT (6 < pT,trig < 10 GeV/c), away-side yield varies with pT,assoc

For lower pT,assoc (1.3 < pT,assoc <1.8 GeV/c), away-side correlation has non-gaussian shape becomes doubly-peaked for lower pT,trig

pedestal and flow subtracted

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

M. Horner, QM 2006

“Reappearance of away-side jet”With increasing trigger pT, away-side jet correlation reappears

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

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

Dijets from dihadrons

NOT background subtracted: no ambiguities from background model

At high trigger pT, high associated pT:

clear jet-like peaks seen on near and away side in central Au+Au

8 < pT(trig) < 15 GeV/c

pT(assoc)>6 GeVSTAR PRL 97 (2006) 162301

d+Au

1/N

trig

dN

/d(

)

Au+Au 20-40% Au+Au 0-5%

Surface Bias of Di-Jets?

Renk and Eskola, hep-ph/0610059

8 < pT,trig< 15 , 4< pT,assoc< 6 GeV/c

8 < pT,trig< 15 GeV/c

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

Comparison of IAA to RAA

IAA = Yield(0-5% Au+Au) Yield(d+Au)

In the di-jets where trigger pT is 8-15 GeV/c, the suppression is same as for single particles as a function of pT

= Near-side IAA

= Away-side IAA

8 < pT(trig) < 15 GeV/c

D. Magestro, QM 2005

Modification of Clean SignalsAway-side yield strongly suppressedAway-side yield strongly suppressed

(almost) to level of R(almost) to level of RAAAA

No dependence on zNo dependence on zTT in measured range in measured range

No modification in shape in transverse or No modification in shape in transverse or longitudinal directionlongitudinal direction

The jets you can see cleanly are also in some The jets you can see cleanly are also in some sense the least modifiedsense the least modified

STAR PRL 97 (2006) 162301

Near-side Yields vs. zT

After subracting the Ridge M. Horner, QM 2006

Away-side Yields vs. zTM. Horner, QM 2006

Away-side suppression as a function of pT,trig

M. Horner, QM 2006

Away-side IAA

Away-side suppression reaches a value of 0.2 for trigger pT > 4 GeV/c, similar to single-particle suppression

IAA (Jet-correlated Yield in AA) / (Jet-correlated Yield in pp)

Where does the energy go? Lower the associated pLower the associated pTT to search for radiated energy to search for radiated energy Additional energy at low pAdditional energy at low pTT BUT no longer BUT no longer

collimated into jetscollimated into jetsActive area: additional handles on the properties Active area: additional handles on the properties of the medium?of the medium?Mach shocks, Cherenkov cones …Mach shocks, Cherenkov cones …

e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) e.g. Renk and Ruppert, Phys. Rev. C 73 (2006) 011901 011901

PHENIX preliminary

Leadinghadrons

Medium

away

near

M. Horner, QM2006

STAR, Phys. Rev. Lett. 95 (2005) 152301 pT (GeV/c)

AA

/pp

STAR preliminary

0-12% 200 GeV Au+Au

- CorrelationsPhys. Rev. C73 (2006) 064907

mid-central Au+Aupt < 2 GeV

d+Au, 40-100% Au+Au, 0-5%

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

0.8< pt < 4 GeVSTAR PRC 75(2007) 034901

/√

ref

In Au+Au: broadening of the near-side In Au+Au: broadening of the near-side correlation in correlation in

Seen in multiple analysesSeen in multiple analyses Number correlations at low pNumber correlations at low pTT

PRC73 (2006) 064907PRC73 (2006) 064907 PPTT correlations at low p correlations at low pTT, for , for

multiple energiesmultiple energies Major source of pMajor source of pTT fluctuations fluctuations J. Phys. G 32, L37 (2006)J. Phys. G 32, L37 (2006) J. Phys. G 34, 451 (2007)J. Phys. G 34, 451 (2007)

Number correlations at Number correlations at intermediate pintermediate pTT

PRC 75, 034901 (2007)PRC 75, 034901 (2007) Number correlations with Number correlations with trigger particles up to 8 GeV/ctrigger particles up to 8 GeV/c

D. Magestro, HP2005D. Magestro, HP2005 J. Putschke, QM2006J. Putschke, QM2006

Near-side Correlation

Additional long-range correlation in

Au+Au 20-30%

the “ridge”

Coupling of high pT partons to longitudinal expansion - Armesto et al, PRL 93 (2004)QCD magnetic fields- Majumder et al, hep-ph/0611035In recombination framework: Coupling of shower partons to thermal partons undergoing longitudinal expansion- Chiu & Hwa Phys. Rev. C72:034903,2005Radial flow + trigger bias –S.A. Voloshin, Nucl. Phys. A749, 287 (2005)

J. Putschke, QM 2006Au+Au 0-10%

STAR preliminary

Study near-side yields

Study away-side correlated yields and shapes

Components

near-side jet peak

near-side ridge

v2 modulated background

Strategy:

Subtract from projection: isolate

ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge() Jet()Can also subtract large .

3<pt,trigger<4 GeV

pt,assoc.>2 GeVAu+Au 0-10%

preliminary

Two-Component Ansatz

(J+R)

||<1.7

J = near-side jet-like corrl.

R = “ridge”-like corrl.

v2 modulated bkg. subtracted

(J+R)

||<1.7

flow (v2)corrected

Extracting near-side “jet-like” yields

1

Au+Au 20-30%

2

2

(J+R)- (R)

con

st b

kg.

sub

tra

cte

d

(J

)

||

<0.

7

(J)

no bkg. subtraction

const bkg. subtracted

(J)

||<0.7

J. Putschke, QM 2006

The “Ridge” + “Jet” yield vs Centrality 3<pt,trigger<4 GeV

pt,assoc.>2 GeVAu+Au 0-10%

preliminaryJet+Ridge ()Jet ()Jet)

yie

ld

,

)Npart

““Jet” yield constant with NJet” yield constant with Npartpart

JJöörn Putschke, QM2006rn Putschke, QM2006

Reminder from pReminder from pTT<2 GeV: <2 GeV:

elongated structure already in minbias AuAu elongated structure already in minbias AuAu

elongation in p-p elongation in p-p to to elongation in AuAu. elongation in AuAu.

STAR, PRC 73, 064907 (2006)

/√

ref

STAR preliminary

“Jet” spectrum vs. “Ridge” spectrum

“jet” slope“ridge” slopeinclusive slope

efft Tptt epdpdN //

J. Putschke, QM 2006

STAR preliminary STAR preliminary

Ridge Yield

pt,assoc. > 2 GeV

STAR preliminary

Ridge yield persists up to highest trigger pT and approximately constant yield

J. Putschke, QM 2006

Particle production in jet distinctly different than

in medium

Associated particle production (B/M ratio) similar in ridge and mediumand about a factor 2-3 different than in the jet. Ridge and medium have similar production mechanism ? Recombination ?

/K~1 /K~0.5

Extending the ridge: correlations to =5Trigger: 3<pT

trig<4 GeV/c, A.FTPC: 0.2<pTassoc< 2 GeV/c, A.TPC: 0.2<pT

assoc< 3 GeV/c

Trigger on mid- associated particle high (reverse of FMS)

Near-side correlation: consistent with zero (within large v2 errors)

Away-side correlations are very similar (when scaled)

Energy loss picture is the same for mid- and forward ?

AuAu 0-10%AuAu 0-5%

AuAu 60-80%

STAR Preliminary

2.7<|assoc|<3.9

Levente Molnar, QM2006

STAR Preliminary

STAR preliminary

0-12% 200 GeV Au+Au

How to interpret shape modifications?

Hard-soft: Hard-soft: away-side spectra approaching the bulk. away-side spectra approaching the bulk.

Deflected jets, Mach-cone shock waves, Cherenkov Deflected jets, Mach-cone shock waves, Cherenkov radiation, completely thermalized momentum radiation, completely thermalized momentum conservation, or…?conservation, or…?

Mediumaway

near

deflected jets

away

near

Medium

mach cone

M. Horner, QM2006

STAR Collaboration, PRL 95,152301 (2005)

STAR preliminary

0-12% 200 GeV Au+Au

Hard-soft correlations

Hard-soft: Hard-soft: away-side spectra approaching the bulk. away-side spectra approaching the bulk.

Inclusive in top 5%?Inclusive in top 5%?

Three-particle correlation – N.N. Ajitanand, J. UleryThree-particle correlation – N.N. Ajitanand, J. Ulery

Mediumaway

near

deflected jets

away

near

Medium

mach cone

STAR, PRL 95,152301 (2005)

4 < pT,trig< 6 GeV/c

Three particle correlationsTwo Analysis Approaches:• Cumulant Method

Unambiguous evidence for true three particle correlations.

• Two-component Jet+Flow-Modulated Background Model

Within a model dependent analysis, evidence for conical emission in central Au+Au collisions

pTtrig=3-4 GeV/c

pTassoc=1-2 GeV/c

off-

diag

onal

pro

ject

ion

d+Au

0-12% Au+Au

=(12)/2

Δ2

Δ1 Δ1

0-12% Au+Au: jet v2=0

Δ2

C. Pruneau, QM2006J. Ulery, HP2006 and poster, QM2006

What other handles do we have?

Centrality, trigger and associated pCentrality, trigger and associated pTT,….. ,…..

…….Reaction plane.Reaction plane

In-plane

Out-planeSTAR

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

STAR, Phys. Rev. Lett. 93 (2004) 252301

Another handle: -jet

q

Photon-jet measurement is, in principle, sensitive to full medium

Bias to where away-side jet is close to surface?

Together with di-jet measurement for comparison

Another differential observable

Increasing ratio of direct photons to decay photons with centrality due to hadron suppression at high pT

PHENIX, Phys. Rev. Lett. 94, 232301 (2005)

Wang et al., Phys.Rev.Lett. 77 (1996) 231-234

1

/Ntr

igdN

/d

(rad)

Another handle: -jetCurrent Results from Run-4 Current Results from Run-4

Au+Au collisions:Au+Au collisions:

J. Jin, QM 2006T. Dietel, QM 2005

q

Summary Limited information extracted from single-particle pLimited information extracted from single-particle pTT

spectra spectra Effective fractional energy loss reaches 20% for Effective fractional energy loss reaches 20% for

most central collisionsmost central collisions Initial energy density ~ 15 GeV/fmInitial energy density ~ 15 GeV/fm33 from radiative from radiative

energy loss models energy loss models Di-Jets (those that are observed) may have less Di-Jets (those that are observed) may have less

surface biassurface bias Photon-Jet Measurement will complement the di-jet Photon-Jet Measurement will complement the di-jet

for more complete probefor more complete probe Heavy-flavor suppression not consistently described Heavy-flavor suppression not consistently described

by theoretical models with light meson suppression – by theoretical models with light meson suppression – need elastic energy lossneed elastic energy loss