1

Wolf G. HolzmannWolf G. Holzmann

Will review critical aspectsWill review critical aspectsof jet medium interaction at of jet medium interaction at RHIC (with emphasis onRHIC (with emphasis onPHENIX results)… PHENIX results)…

… … then discuss potential forthen discuss potential forstudying the medium studying the medium response to jet quenchingresponse to jet quenchingwith the ATLAS detector at with the ATLAS detector at the LHCthe LHC

2

dy

dE

RT

Bj0

2

11

τπε =

εBjorken~ 5 - 15 GeV/fm3

~ 35 – 100 ε0

high energydensities quark dof

Evidence for stronglyEvidence for stronglyinteracting partonic matterinteracting partonic matteris compelling !is compelling !

Strongly Interacting Matter at RHIC

stronglycoupled

3

Jets as a tomographic probe of the medium

coneRFragmentation:

hadron

parton

pz

p≡

Jets in h+h Jets in h+h collisionscollisions

coneRFragmentation:

hadron

parton

pz

p≡

Jets in HI Jets in HI collisionscollisions

Gyulassy et al., nucl-th/0302077

Jet modification sensitive to gluon densities, path length, …Jet modification sensitive to gluon densities, path length, ….Jets as Tomographic Probes of the Medium!

4

Phys. Rev. Lett. 90, (2003)

STAR

Jets via:Two Particle Correlations

Jets via:Nuclear Modification Factor

( )( )Events ppin Yield

EventsAu Auin Yield

+•

+=

BARAA

High pT Jet Modification in Au+Au

Strong jet modification observed in Au+AuStrong jet modification observed in Au+Au

How is the energy taken up by the medium ?

5

nucl-ex/0507004

T. Renk, J. Ruppert hep-ph/0509036

Strong centrality dependent modification Strong centrality dependent modification of away-side jet in Au+Auof away-side jet in Au+Au

Possible mechanismsPossible mechanismsmach-cone scenariomach-cone scenario

nucl-th/0406018 Stoeckerhep-ph/0411315 Casalderrey-Solana, et al

Not the only explanation:Not the only explanation:

Cherenkov gluon radiation: nucl-th/0507063 Koch, Majumder, X.-N. Wang

Jets and Flow couple: hep-ph/0411341 Armesto,Salgado,Wiedemann

Intermediate pT Jet induced Correlations

Can two particle correlationsCan two particle correlationsprovide constraints for theseprovide constraints for theseconjectures?conjectures?

6

D D

Characterize away-side shape via:

RMS : measures width of away-side peak

Kurtosis : <(π)4>/RMS2, the 4th central moment, measures “gaussian-ness” of peak (= 3 for

Gaussian)

D : distance between away-side peak and π from double gaussian fit -> approximates peak-position

Let’s take a closer Look at these Shapes

7

Shape modification apparently largely independent of system Shape modification apparently largely independent of system size and beam energy in range root(s) ~ 64 -200 GeV !size and beam energy in range root(s) ~ 64 -200 GeV !

Energy and System Size Dependence of Shape Parameters

8

But medium not too different over this range …

Consistent with intermediate pConsistent with intermediate pT T shape modification shape modification

being dominated by medium response to jetbeing dominated by medium response to jet

9

PHENIX Preliminary

[1] Majumder, Wang, nucl-th/0507062

[2] Koch, Majumder, Wang, nucl-th/0507063

Weak pWeak pT T dependence poses dependence poses

challenges for earlychallenges for earlygluon Cherenkov radiation gluon Cherenkov radiation models which predicted a models which predicted a

strong trend with pstrong trend with pTT

pT Dependence of Shape Parameters

10

MesonMeson vs. vs. BaryonBaryon associated partner (for fixed Hadron associated partner (for fixed Hadron trigger)trigger)

PHENIX Preliminary

Jet associated mesons and baryons Jet associated mesons and baryons show similar shape modification show similar shape modification

Jet Associated Identified Particle Correlations

11

If away-side parton is deflectedIf away-side parton is deflectedin medium, followed by normalin medium, followed by normaljet fragmentation, expect little jet fragmentation, expect little change in the away-side jet change in the away-side jet particle species compositionparticle species composition

Particle ratios inside jet can give insight!Particle ratios inside jet can give insight!

Can PID dependent jet correlations constrain deflection?

12

MesonMeson vs. vs. BaryonBaryon associated partner (for fixed Hadron associated partner (for fixed Hadron trigger)trigger)

Jet Associated Baryon to Meson Ratio

Baryon/meson ratio trend in jets qualitatively similar to Baryon/meson ratio trend in jets qualitatively similar to baryon/meson ratio trend of bulk matter.baryon/meson ratio trend of bulk matter.

Same mechanism?Same mechanism?

13

Remember …

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Single particle baryon/meson ratio well described by Single particle baryon/meson ratio well described by recombination models.recombination models.

Constituent quark scaling of elliptic flow.Constituent quark scaling of elliptic flow.

Greco & Konucl-th/0405040

14

coneR

Data is not inconsistent with a picture where Data is not inconsistent with a picture where partons from shock wave “remember” jet direction.partons from shock wave “remember” jet direction.The jet and it’s medium excitation are correlated.The jet and it’s medium excitation are correlated.

Jet quenching can introduce 2-Jet quenching can introduce 2-body correlations between the body correlations between the jet and the medium:jet and the medium:

R. Fries, S. Bass and B. Mueller nucl-th/0407102

One Possible Scenario

15

Can we do energy calibrated studies of the medium response?

• Normal dijet (πo-h):

– Trigger bias: Eπ < Ejet,, <z>~0.75

– Possible surface bias

• Direct tagged jet:

– No fragmentation: E ~ Ejet

– No strong interaction, sensitive

to the whole medium

Proposed in hep-ph/9605213Proposed in hep-ph/9605213~10 years ago~10 years ago

Fix maximum jet energy that Fix maximum jet energy that can be transferred to the can be transferred to the medium, check for consistencymedium, check for consistencyin medium response.in medium response.

16

generate incl. generate incl. -h per trigger yield-h per trigger yield

Methodology in a Nutshell

generate decay generate decay -h per trigger yield-h per trigger yield

(Use pair by pair waiting with MC factor (Use pair by pair waiting with MC factor for prob. That for prob. That ππ at given p at given pT T decays todecays to

in pin pT T range of interest)range of interest)

p+psubtract decay subtract decay -h per trigger yield-h per trigger yieldfrom from -h per trigger yield-h per trigger yield

# inclusive # inclusive ##decay decay

R=R=

€

Ydir−h

= 1R−1

RYinc−h−Ydec−h( )

17

PHENIX Preliminary PHENIX Preliminary

• data PYTHIA PYTHIA 6.1 kT = 2.5 GeV

-h Correlations in p+p

M. Nguyen (Stony Brook)

Reasonable agreement between data and PYTHIAReasonable agreement between data and PYTHIA

18

Black: Au+Au Red: p+p

1/N

trigd

N/d

(rad) Jiamin Jin (Columbia)

-h Correlations in Au+Au

We have the tools,We have the tools,we just need the statistics…we just need the statistics…

19

Possible Modification of Jet Topology

hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaneynucl-th/0406018 Stoeckerhep-ph/0503158 Muller,Ruppert

Wake Effect or “sonic boom”

nucl-th/0507063 Koch, Majumder, X.-N. Wang

Cherenkov Gluon Radiation

wrong pwrong pTT dependence? dependence?

wrong particle composition in jet?wrong particle composition in jet?

Two-Particle Correlation data does not proof mach-cone Two-Particle Correlation data does not proof mach-cone but it seems consistent with it.but it seems consistent with it.

Bending Jets

20

Jet tomography at LHC

Can (and will) do RHIC type studies with better statisticsCan (and will) do RHIC type studies with better statistics

Can (and will) do high pCan (and will) do high pTT jet reconstruction jet reconstruction

(event-by-event jet tomography, event-by-event medium (event-by-event jet tomography, event-by-event medium response opposite reconstructed jet…)response opposite reconstructed jet…)

How can jet studies at the LHC improve on the situation?How can jet studies at the LHC improve on the situation?

Truly high pTruly high pTT jets will be jets will be

produced copiously in produced copiously in Pb+Pb collisions at the LHCPb+Pb collisions at the LHC

21

My personal detector wish-list for studying medium My personal detector wish-list for studying medium response to jet quenching at the LHC:response to jet quenching at the LHC:

Full azimuth and large pseudorapidity coverage toFull azimuth and large pseudorapidity coverage tostudy event shapes opposite a reconstructed jetstudy event shapes opposite a reconstructed jet

Excellent capabilities to study global medium propertiesExcellent capabilities to study global medium properties

Excellent calorimetry for full event-by-event jet Excellent calorimetry for full event-by-event jet reconstructionreconstruction

The ATLAS Detector has all these capabilities!The ATLAS Detector has all these capabilities!

Based on the previous slides …

Excellent photon identification capabilityExcellent photon identification capability

22

ATLAS Calorimetery Hadronic Barrel

Hadronic EndCap

EM EndCap

EM Barrel

Forward

Finely segmented calorimeter coverage over full rangeand large range

The ATLAS Calorimeter

23

(Di)jets from PYTHIA (Di)jets from PYTHIA in Calorimter Towersin Calorimter Towers

embedded in embedded in HIJING eventHIJING event

Measuring Jets in The ATLAS Calorimeter

Energetic jets clearly visible over the heavy ion backgroundLarge coverage is important

24

Jet

Background

Jet

Background

All too wide for single photons

x = 0.0028 x 0.1

– Segmentation of first EM sampling layer so fine that heavy ion background is ~ negligible (unique at LHC)

– Fine -> rejection of neutral hadron decays

– Clean 1st sampling-> prompt isolation

Taking a closer look

25

Two Approaches to Jet Reconstruction in ATLAS

A) Seeded Cone Algorithm

Original cellsOriginal cells Cloned cellsCloned cells

Original towersOriginal towers

Subtracted cellsSubtracted cells

New towersNew towers

Reconstructed jetsReconstructed jets

Layer-by-layersubtraction(exclude seeds)

Currently also lookingCurrently also lookingat methods to improveat methods to improvealgorithm: seed selection,algorithm: seed selection,background subtraction, …background subtraction, …

First approach: First approach: use standard p+p cone algorithm use standard p+p cone algorithm with background subtractionwith background subtraction

26

Jet Energy Resolution with Seeded Cone Algorithm

Study of different event samples embeddedinto central Pb+Pb HIJING (b=0-2 fm)

Results obtained from standard p+p Results obtained from standard p+p cone algorithm w/ backgr.- subtractioncone algorithm w/ backgr.- subtractionSome recalibration still needed.Some recalibration still needed.

27

B) KT Algorithm clusters particles close in phase-space:

dij = min(k2ti,k2

tj)R2 , where R2=(i-j)2+(i-j)2

Kt algorithm purposefully mimics a walk backwardsalong the fragmentation

chain

for all possible combinations: O(N3)

Cacciari et al: “Fast” Kt optimization to O(NlogN)

Two Approaches to Jet Reconstruction in ATLAS

diB = k2ti

28

How fast is fast?

“Fast” Kt algorithm outperforms cone algorithm,Becomes feasible in heavy ion environment!

M. Cacciari et al, hep-ph/0512210

29

Real Jets appearas narrow towers

“Fake” Jetsappear flat and broad

UseUse jet topology to discriminate between jets and backgroundjet topology to discriminate between jets and background!!

“Fast” Kt Finder: Discriminating Jets and Background

30

3 4

21

34

1

2

Initial look seems promising.Initial look seems promising.Other variables can also be Other variables can also be constructed. constructed.

E T,max = maximum ET in calo cell

<E T > = average ET in calo cell

Discriminating Jets and Background: A First Look

31

Can we control the flowing background?

Presampler Layer 1 Layer 2 Layer 3

Yes! Can measure dN/dϕ in different layers

(and sections) of calorimeters e.g. EM Barrel

η

ϕ ϕ ϕ ϕ

ϕ ϕ ϕ ϕ

η η η

32

Reaction Plane Resolution

ATLAS has excellent reaction plane resolution!ATLAS has excellent reaction plane resolution!

33

PYTHIA + jet (75 GeV) superimposed on b=4 fm HIJING Pb+Pb event, full GEANT

Jet

+Jet in ATLAS

34

EM

Layer

1 E

T

(GeV

)

Isolated photon gives clean signal in EM first sampling layer

Even in central Pb+Pb !

One (of 64) rows in barrel EM calorimeter 1st sampling layer

Δη×Δϕ = 0.003x0.1

+Jet in ATLAS

35

PYTHIA + jet (75 GeV) superimposed on b=4 fm HIJING Pb+Pb event, full GEANT

Background subtracted

Jet

+Jet in ATLAS

36

+Jet in ATLAS

Direct triggered angularcorrelationsenergy calibrated: - jet studies - mach cone studies

Photon bremsstrahlung injet cone?

Many interesting possibilities: let your imagination run wild :-)

37

Summary

Di-hadron away-side modification at intermediate pT at RHIC showscharacteristics of medium response to jet quenching

Consistent with (but no proof of) mach cone type scenario, pT and PID dependent correlations can provide constraints for models

ATLAS detector uniquely suited to study jet medium interactionsat the LHC

Lots of ground work on jet and flow reconstruction in heavy ion Environment (seeded cone algorithm, fast Kt algorithm, different Background subtraction schemes, etc…) being done in ATLAS

Studies shown only an “amuse gueule”, see N. Grau’s talk on Sunday

New collaborators are welcome!

38

★★ ★★★

★★

★

★

M. Baker, R. Debbe, A. Moraes, R. Nouicer, P. Steinberg, H. Takai, F. Videbaek, S. WhiteBrookhaven National Laboratory, USA

J. Dolejsi, M. SpoustaCharles University, Prague

A. Angerami, B. Cole, N. Grau, W. Holzmann, M. LelchoukColumbia Unversity, Nevis Laboratories, USA

A. Olszewski, B. Toczek, A. Trzupek, B. Wosiek, K. WozniakIFJ PAN, Krakow, Poland

L. RosseletUniversity of Geneva, Switzerland

J. Hill, A. Lebedev, M. RosatiIowa State University, USA

G. Atoian, V. Issakov, H. Kasper, A. Poblaguev, M. ZellerYale University, USA

A. DenisovIHEP, Russia

P. Chung, J. Jia, R. Lacey, N N.. AjitanandChemistry Department, Stony Brook University, USA

V. PozdnyakovJINR, Dubna, Russia

S. TimoshenkoMePHI, Moscow, Russia

ATLAS HI Working Group

39

40

DELPHI

Baryon yield dependence Baryon yield dependence consistent with jet physicsconsistent with jet physics

in e-e collisionsin e-e collisions

Baryon yield dependence Baryon yield dependence consistent with jet physicsconsistent with jet physics

in e-e collisionsin e-e collisions

41

i.e. Zero Yield At Minimum (ZYAM)

( ) ( ) ( )

0

HarmoC Jet Functiorrelation Function onic n

C a H Jφ φφ⎡ ⎤

ΔΔ⎢ ⎥Δ = +⎢ ⎥⎣ ⎦

64 6 748 876 7 8

( ) ( ) ( )0

0

Jet Function

JC a H

aφ

φ φΔ

Δ − Δ⎡ ⎤⎣ ⎦=6 7 8

( )min 0J φΔ =

a0 is obtained without putting any constraint on the Jet shape by requiring

Two source model : Flow (H) & Jet (J)

N.N. Ajitanand et al.N.N. Ajitanand et al.Phys. Rev. C 72, 011902 (2005)Phys. Rev. C 72, 011902 (2005)

2

vary

~ 0

out

c

Operational Demonstration

untill v

Unconstrained harmonic

Constrained

High pt particle constrainedperpendicular to RP

Constraint byte

Rψ

1 (A) LP

2 (B)

12

c

Decomposition of Flow and Jet Signals

Subtraction Extinction

Reliable Decomposition of Flow and Jet Reliable Decomposition of Flow and Jet

Signals via two separate MethodsSignals via two separate Methods

42

Test of Ansatz

Simulation

Strong Away-Side Modification in Au+Au Revealed via Both MethodsStrong Away-Side Modification in Au+Au Revealed via Both Methods

ZYAM subtracted J(ZYAM subtracted J())

Flow extinguished C(Flow extinguished C() = J() = J())

Data

Both Methods Agree!

Phys. Rev. C 72, 011902 (2005)Phys. Rev. C 72, 011902 (2005)

43

∑ ∑ = )(/)(0 φφ CJaJPFJet-Pair Fraction:

BtB

tAt

ABt n

nn

nJPFCY ×

××=Efficiency corrected

Conditional yield (CY):

BtBA

AB

nnn

nJPFCY ×

××=Efficiency corrected

Conditional yield (CY):

Eff. Corrected pair rate

Eff. Corrected Singles yields

Recorded values

( ) ( ) ( )

0

HarmoC Jet Functiorrelation Function onic n

C a H Jφ φφ⎡ ⎤

ΔΔ⎢ ⎥Δ = +⎢ ⎥⎣ ⎦

64 6 748 876 7 8Two Source Model

44

One approach: One approach: fix fix εε via N via Npartpart, ,

vary path length by vary path length by looking in and out of looking in and out of

reaction planereaction plane

One approach: One approach: fix fix εε via N via Npartpart, ,

vary path length by vary path length by looking in and out of looking in and out of

reaction planereaction plane

What are the relative influences of:What are the relative influences of:Energy-densityEnergy-density

Path-length (L, LPath-length (L, L22, L, Laa))

What are the relative influences of:What are the relative influences of:Energy-densityEnergy-density

Path-length (L, LPath-length (L, L22, L, Laa))

nucl-ex/0409015

Need to look at problem in several different ways to pin down mechanisticdetails!

D. Winter, WWND2006STAR, PRL 93 (2004) 252301

Mechanistic Details of Jet Modification

45

No striking difference in modification pattern observed for Au+Au No striking difference in modification pattern observed for Au+Au and Cu+Cu at the same Npart! Small differences in yield canand Cu+Cu at the same Npart! Small differences in yield can

cerve to constrain path length dependent modelscerve to constrain path length dependent models

Energy density major actor!Energy density major actor!Energy density major actor!Energy density major actor!

Per Trigger Yields can give additional constraints

46

47

48

Jet Position Resolution with Seeded Cone Algorithm

Results obtained from standard p+p Results obtained from standard p+p cone algorithm w/ backgr.- subtractioncone algorithm w/ backgr.- subtractionSome recalibration still needed.Some recalibration still needed.

Resolutions in and for <ET>~50 GeV

49

Jet

Background

Jet

Background

All too wide for single photons

x = 0.0028 x 0.1

– Segmentation of first EM sampling layer so fine that heavy ion background is ~ negligible

– Fine -> rejection of neutral hadron decays

– Clean 1st sampling-> prompt isolation

The ATLAS Calorimeter

50

The ATLAS Calorimeter

Δη×Δϕ in LAr Barrel:Layer 1: 0.003x0.1Layer 2: 0.025x0.025Layer 3: 0.05x0.025

Finely segmented calorimeter coverage over full rangeand large range

51

Infrared and collinear safe

Exceptionally suited to study jet sub-structure: - modification of jet topology in Pb+Pb - hard radiation within the jet

New ways to distinguish jets and background

Systematic cross-check to cone algorithm

Advantages of “Fast” Kt Algorithm

52

Possible Modification of Jet Topology

hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaneynucl-th/0406018 Stoeckerhep-ph/0503158 Muller,Ruppert

Wake Effect or “sonic boom”

nucl-th/0507063 Koch, Majumder, X.-N. Wang

Cherenkov Gluon Radiation

hep-ph/0411341 Armesto,Salgado,Wiedemann

Jets and Flow couple

Can we use jets to probe the equation of state at RHIC?Can we use jets to probe the equation of state at RHIC?

53

Particle species dependent properties of bulk matter

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

54

coneR

R. Fries, S. Bass and B. Mueller nucl-th/0407102

55

MesonMeson vs. vs. BaryonBaryon associated partner (for fixed Hadron associated partner (for fixed Hadron trigger)trigger)

Jet Associated Identified Conditional Yields

Different pT trends of jet associated mesons and baryonsDifferent pT trends of jet associated mesons and baryons

56

System size and energy dependence

central peripheral

57

dNdNchch/d/d very similar for Au+Au and Cu+Cu at the same N very similar for Au+Au and Cu+Cu at the same Npartpart ! !

At RHIC almost all transverse energy At RHIC almost all transverse energy goes into particle productiongoes into particle production

Complementary opportunity for jet-tomography:Complementary opportunity for jet-tomography:-> fix energy density-> fix energy density-> vary path length -> vary path length

nucl-ex/0409015

Energy Density versus Path Length Effects

58

No striking difference in modification pattern observed for Au+Au No striking difference in modification pattern observed for Au+Au and Cu+Cu at the same Npart!and Cu+Cu at the same Npart!

Energy density major actor!Energy density major actor!Energy density major actor!Energy density major actor!

π

Jets via:Nuclear Modification Factor

( )( )Events ppin Yield

EventsAu Auin Yield

+•

+=

BARAA

Jets via:Two Particle Correlations

Jet Modification in Au+Au and Cu+Cu

59

We can use three parameters to characterize away side shape1. RMS : <(-π)2>, the width of the

distribution, the 2nd central moment.2. Kurtosis : <(-π)4>/RMS2, the 4th

central moment, equals to 3 if Gaussian.

3. D : half distance between the double peaks, a double gaussian fit.

D D

0-10% 30-40% 60-90%