[PPT] - Jet Quenching in the light of Experimental perturbative QCD PowerPoint Presentation

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Jet Quenching in the light of perturbative QCD

Korinna Zapp

in collaboration with F. Krauss and U. Wiedemann

Institute for Particle Physics Phenomenology

Birmingham Particle Physics Seminar 09. 05. 2012

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Outline

Experimental findings Analytical approach MC approach Conclusions

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Differential jet cross section

ATLAS, arXiv:1112.6297

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Fragmentation function

F(z)

1

10 1 10

2

10

3

10

< 500 GeV

T jet

400 GeV < p ATLAS = 7 TeV s

1

L dt = 36 pb

∫

Data Pythia6 AMBT1 Pythia6 MC09 Pythia6 Perugia 2010 Herwig+Jimmy Herwig++ 2.4.2 Herwig++ 2.5.1 Sherpa Pythia8 8.145 4C

z

2

10

1

10

(MC-Data)/Data (%)

60
40
20

20 40 60

z

2

10

1

10

(MC-Data)/Data (%)

60
40
20

20 40 60

z = pjet · ptrack p2

jet

ATLAS, Eur. Phys. J. C 71 (2011) 1795

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Jet shapes

(r) Ψ 0.5 0.6 0.7 0.8 0.9 1 1.1 jets R = 0.6

t

anti-k < 110 GeV

T

80 GeV < p | y | < 2.8

ATLAS

1

dt = 3 pb L

∫

Data PYTHIA-Perugia2010 HERWIG++ ALPGEN PYTHIA-MC09

r

0.1 0.2 0.3 0.4 0.5 0.6

DATA / MC

0.9 0.95 1 1.05 1.1

r =

(∆φ)2 + (∆y)2

ATLAS, Phys. Rev. D 83 (2011) 052003

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Jets in Pb+Pb

tracks: p⊥ > 2.6 GeV calorimeter cells: E⊥ > 0.7/1 GeV

AJ = E⊥1 − E⊥2 E⊥1 + E⊥2

E⊥1 > 100 GeV E⊥2 > 25 GeV

◮ clear energy asymmetry between jets ◮ jet axis largely unchanged

ATLAS, Phys. Rev. Lett. 105 (2010) 024901

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Heavy ion challenge

◮ jet reconstruction challenging due to large background ◮ maybe look for more robust observables. . .

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Single-inclusive hadron suppression

RAA(p⊥) = dNAA/dp⊥ NcolldNpp/dp⊥ = spectrum in A+A Ncoll × spectrum in p+p

(GeV/c)

T

p 5 10 15 20

2

) (GeV/c)

T

dp η ) / (d

ch

N

2

) (d

T

p π 1/(2

evt

1/N

8

10

7

10

6

10

5

10

4

10

3

10

2

10

1

10 1 10

2

10

3

10

4

10

5

10 scaled pp reference 0-5% 70-80% = 2.76 TeV

NN

s Pb-Pb (GeV/c)

T

p 5 10 15 20

AA

R 0.1 1 = 2.76 TeV

NN

s Pb-Pb 0 - 5% 70 - 80%

ALICE, Phys. Lett. B 696 (2011) 30

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Single-inclusive hadron suppression

(GeV/c)

T

p

1 2 3 4 56 10 20 30 100

AA

R

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

70-90%

and lumi. uncertainty

AA

T CMS PbPb |<1.0 η = 2.76 TeV, |

NN

s

(GeV/c)

T

p

1 2 3 4 56 10 20 30 100

AA

R

0.2 0.4 0.6 0.8 1 1.2

10-30% (GeV/c)

T

p 1 2 3 4 56 10 20 30 100 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 50-70% (GeV/c)

T

p 1 2 3 4 56 10 20 30 100 0.2 0.4 0.6 0.8 1 1.2 5-10% (GeV/c)

T

p 1 2 3 4 5 10 20 30 100 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 30-50% (GeV/c)

T

p 1 2 3 4 5 10 20 30 100 0.2 0.4 0.6 0.8 1 1.2 0-5%

CMS, Eur. Phys. J. C (2012) 72:1945

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Heavy ion collisions

◮ high multiplicity ◮ nuclei large objects (radius ∼ 7 fm) ◮ expect extended system with very high density ◮ estimate of initial energy density: ǫ0 ≃ 5.5 GeV fm3 at RHIC

and ǫ 40 GeV

fm3 at LHC ◮ theoretical expectation: nucleons melt around 1 GeV fm3

→ quark gluon plasma

◮ naive picture

◮ jets involve high scale → early production

◮ apparently: interactions in dense medium

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Heavy ion collisions

◮ high multiplicity ◮ nuclei large objects (radius ∼ 7 fm) ◮ expect extended system with very high density ◮ estimate of initial energy density: ǫ0 ≃ 5.5 GeV fm3 at RHIC

and ǫ 40 GeV

fm3 at LHC ◮ theoretical expectation: nucleons melt around 1 GeV fm3

→ quark gluon plasma

◮ naive picture

◮ jets involve high scale → early production

◮ apparently: interactions in dense medium

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Jet quenching

Motivation

◮ ’deep inelastic scattering’ of jet on medium ◮ interplay between weakly and strongly coupled regimes ◮ emergence of collectivity from microscopic theory of

individual quanta

Executive summary of experimental findings

◮ strong suppression of hadron production at large p⊥ ◮ reduction of jet energy ◮ fragmentation function inside remainder jet looks as in

vacuum

◮ jet axis remains unchanged ◮ soft modes get transported to large angles

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Jet quenching

Motivation

◮ ’deep inelastic scattering’ of jet on medium ◮ interplay between weakly and strongly coupled regimes ◮ emergence of collectivity from microscopic theory of

individual quanta

Executive summary of experimental findings

◮ strong suppression of hadron production at large p⊥ ◮ reduction of jet energy ◮ fragmentation function inside remainder jet looks as in

vacuum

◮ jet axis remains unchanged ◮ soft modes get transported to large angles

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Gluon radiation in eikonal limit

q(2)

⊥

q(1)

⊥

q(N)

⊥

.............. L

ω, k⊥ E

◮ high energy approximation: E ≫ ω ≫ k⊥, q⊥ ◮ static scattering centres → no collisional energy loss ◮ medium characterised by transport coefficient

ˆ q = q2

⊥

λ

Baier, Dokshitzer, Mueller, Peigne, Schiff, Nucl. Phys. B 484 (1997) 265

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

LPM-effect: heuristic discussion

Brownian motion of the gluon: k2

⊥ = ˆ

qL gluon decoheres from projectile when relative phase ϕ > 1 ϕ =

k2

⊥

2ω L

= ˆ

qL2 2ω = ωc ω formation time of the radiated gluon: tf ≃ 2ω k2

⊥

≃ 2ω ˆ qtf ⇒ tf =

2ω

ˆ q and Ncoh = tf λ gluon energy spectrum: d2I coh dωdz ≃ 1 Ncoh d2I incoh dωdz ∝

ˆ

q 2ω αs ω radiative energy loss: ∆E =

L

dz

ωc

dω ω d2I

dωdz ∝ αsˆ qL2

Baier, Schiff, Zakharov, Ann. Rev. Nucl. Part. Sci. 50 (2000) 37

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Is it any good?

◮ formation time of medium induced emissions:

τmed =

2ω

ˆ q ⇒ soft gluons decohere first. . .

◮ formation angle:

θmed ≈ k⊥ ω = √ˆ qτmed ω = (2ˆ q)1/4 ω3/4 ⇒ . . . and at large angles

◮ formation time of vacuum emissions:

τvac = 2ω k2

⊥

⇒ decoherence of energetic gluons delayed

Casalderrey-Solana, Milhano, Wiedemann, J. Phys. G 38 (2011) 035006

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Confrontation with data

0.2 0.4 0.6 0.8 1 RAA

s 2 HG

6 8 10 12 14 16 18 20 pT (GeV/c) 0.2 0.4 0.6 0.8 RAA

s 2 HG

PHENIX 0 − 5% AMY, b = 2.4 fm, α = 0.33 HT, b = 2.4 fm, q = 1.9 GeV /fm, c = 0.2 ASW, b = 2.4 fm, K = 3.6 PHENIX 20 − 30% AMY, b = 7.5 fm, α = 0.33 HT, b = 7.5 fm, ASW, b = 7.5 fm, K = 3.6 = 1.9 GeV /fm, c = 0.2 q ^ ^ 0

Bass et al., Phys. Rev. C 79 (2009) 024901

◮ but extracted values for transport coefficient ˆ

q0 differ by factor 5

◮ experimentally accessible region not near eikonal limit ◮ calculations are applied outside their range of validity

Armesto et al., arXiv:1106.1106

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Confrontation with data

0.2 0.4 0.6 0.8 1 RAA

s 2 HG

6 8 10 12 14 16 18 20 pT (GeV/c) 0.2 0.4 0.6 0.8 RAA

s 2 HG

PHENIX 0 − 5% AMY, b = 2.4 fm, α = 0.33 HT, b = 2.4 fm, q = 1.9 GeV /fm, c = 0.2 ASW, b = 2.4 fm, K = 3.6 PHENIX 20 − 30% AMY, b = 7.5 fm, α = 0.33 HT, b = 7.5 fm, ASW, b = 7.5 fm, K = 3.6 = 1.9 GeV /fm, c = 0.2 q ^ ^ 0

Bass et al., Phys. Rev. C 79 (2009) 024901

◮ but extracted values for transport coefficient ˆ

q0 differ by factor 5

◮ experimentally accessible region not near eikonal limit ◮ calculations are applied outside their range of validity

Armesto et al., arXiv:1106.1106

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Beyond analytical calculations

Kinematics beyond eikonal limit

◮ phase space restrictions due to E/p-conservation ◮ no clear distinction between elastic & inelastic

scattering

◮ dynamical scattering centres

→ collisional energy loss → radiation off scattering centres

◮ no clear separation of vacuum and medium radiation

Futher limitations of analytical models

◮ single gluon radiation

probabilistic iteration thereof

◮ not suitable for exclusive observables & jets ◮ no control over recoils

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

State of the art MC’s in p+p

(multi-purpose event generators: Herwig, Pythia, Sherpa)

matrix elements: fixed order perturbation theory final state parton shower: resummation of collinear/soft logarithms initial state parton shower: like final state parton hadronisation: non-perturbative QCD: modelling

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Situation in A+A

matrix elements: unmodified due to high scale

final state parton shower: modified by medium interactions

nly calculations for special cases

e.g. single gluon radiation spectrum in eikonal limit

initial state parton shower: found to be unmodified at RHIC

except for pdf’s

hadronisation: probably modified, no theoretical guidance

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL approach

Zapp, Krauss, Wiedemann, arXiv:1111.6838

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL approach

Zapp, Krauss, Wiedemann, arXiv:1111.6838

leave eikonal limit

◮ scattering in medium: pQCD ME

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL approach

Zapp, Krauss, Wiedemann, arXiv:1111.6838

leave eikonal limit

◮ scattering in medium: pQCD ME ◮ scattering in medium: pQCD ME + PS

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL approach

Zapp, Krauss, Wiedemann, arXiv:1111.6838

leave eikonal limit

◮ scattering in medium: pQCD ME ◮ scattering in medium: pQCD ME + PS ◮ need to understand spacio-temporal structure

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL approach

Zapp, Krauss, Wiedemann, arXiv:1111.6838

leave eikonal limit

◮ scattering in medium: pQCD ME ◮ scattering in medium: pQCD ME + PS ◮ need to understand spacio-temporal structure ◮ formation time τ ≃ 1

Q E Q ≃ ω k2

⊥ ◮ emission with shortest formation time wins

SLIDE 27

Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL overview

◮ nuclear pdf’s

EPS09

◮ jet production: hard ME’s and ISR: PYTHIA ◮ FSR and medium interactions: treated on same footing

controlled by formation times

◮ includes LPM effect ◮ take care of colour connection between jet and recoils ◮ hadronisation: PYTHIA

Lund string model

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL scattering cross section

◮ cross section for scattering in medium

σi(E, T) =

|ˆ t|max(E,T)

d|ˆ

t|

xmax(|ˆ t|)

xmin(|ˆ

t|)

dx

j∈{q,¯

q,g}

f i

j (x, |ˆ

t|) dˆ σj d|ˆ t|(xˆ s, |ˆ t|)

◮ keep only leading contribution to partonic cross section

dˆ σ d|ˆ t|(ˆ s, |ˆ t|) ≈ CR2πα2

s(|ˆ

t| + µ2

D)

1 (|ˆ t| + µ2

D)2 ◮ regulated by µ2 D ≈ 3T ◮ requires a ’partonic pdf’ f i j (x, |ˆ

t|)

◮ also need the Sudakov form factor

Sa(Q2, Q2

0) = exp

  −

Q2

Q2

dq2 q2

dz αs(k2

⊥)

2π

b

ˆ Pba(z)

  

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL partonic pdf’s

◮ partonic pdf’s defined through DGLAP equation

f j

i (x, Q2) = Sj(Q2, Q2 0)f j i (x, Q2 0)δij

+

Q2

Q2

dq2 q2 Si(Q2, q2)

zmax

x

dz z αs(k2

⊥)

2π

k

ˆ Pik(z)f j

k (x/z, q2) ◮ at the cut-off scale Q0 one has

f j

i (x, Q2 0) =

δ(1 − x)

; i = j ; i = j

◮ considering at most one emission one gets

f q

q (x, Q2) =Sq(Q2, Q2 0)δ(1 − x)

+

Q2

Q2

dq2 q2 Sq(Q2, q2) αs(k2

⊥)

2π ˆ Pqq(x) etc.

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Probabilistic formulation of the LPM-effect

◮ naive MC purely incoherent ◮ consider gluon radiation with two momentum transfers

Wiedemann, Nucl. Phys. B 588(2000),303

◮ analytical calculation interpolates between

incoherent production τ1 ≪ L

k q1 q2 L GB

coherent production τ1 ≫ L

k q2 q1 L GB

◮ τ1 ≡

2ω (k + q1)2 inverse transverse gluon energy

◮ can be interpreted as gluon formation time

→ momentum transfers during formation time act coherently

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Coherent emission

Kinematics

◮ coherent scattering centres act as one

ne momentum transfer:

ωd3I (1) dωdk ∝

dq |A(q)|2R(k, q)

two momentum transfers: ωd3I (2) dωdk ∝

dq1 dq2 |A(q1)|2|A(q2)|2R(k, q1 + q2)

◮ consistent determiation of scattering centres and

formation time

Emission probability

◮ suppression compared to incoherent emission by factor

1/Ncoh

Ncoh: number of coherent momentum transfers

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Probabilistic formulation of the LPM-effect

ωc/E ω−3 ω−3/2 dI/dω ω/E 0.01 0.00001 0.0001 0.001 0.01 0.1 1 10 0.1 1

L2

L

0.2 0.4 0.6 0.8 1 1.2 1.4 30 25 20 15 10 5

∆E [GeV] 200 150 100 50 0 0 2 4 L/Lc 6 8 10

analytical results:

dI dω ∝ ω−3/2

für ω < ωc

dI dω ∝ ω−3

für ω > ωc deviation in infra-red due to regularisation ∆E ∝ L2 für L < Lc ∆E ∝ L für L > Lc

Zapp, Stachel, Wiedemann, Phys. Rev. Lett. 103 (2009) 152302 Zapp, Stachel, Wiedemann, JHEP 1107 (2011) 118

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Probabilistic formulation of the LPM-effect

ωc/E ω−3 ω−3/2 dI/dω ω/E 0.01 0.00001 0.0001 0.001 0.01 0.1 1 10 0.1 1

L2

L

0.2 0.4 0.6 0.8 1 1.2 1.4 30 25 20 15 10 5

∆E [GeV] 200 150 100 50 0 0 2 4 L/Lc 6 8 10

analytical results:

dI dω ∝ ω−3/2

für ω < ωc

dI dω ∝ ω−3

für ω > ωc deviation in infra-red due to regularisation ∆E ∝ L2 für L < Lc ∆E ∝ L für L > Lc

Zapp, Stachel, Wiedemann, Phys. Rev. Lett. 103 (2009) 152302 Zapp, Stachel, Wiedemann, JHEP 1107 (2011) 118

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Probabilistic formulation of the LPM-effect

ωc/E ω−3 ω−3/2 dI/dω ω/E 0.01 0.00001 0.0001 0.001 0.01 0.1 1 10 0.1 1

L2

L

0.2 0.4 0.6 0.8 1 1.2 1.4 30 25 20 15 10 5

∆E [GeV] 200 150 100 50 0 0 2 4 L/Lc 6 8 10

analytical results:

dI dω ∝ ω−3/2

für ω < ωc

dI dω ∝ ω−3

für ω > ωc deviation in infra-red due to regularisation ∆E ∝ L2 für L < Lc ∆E ∝ L für L > Lc understand prefactor up to 30 %

Zapp, Stachel, Wiedemann, Phys. Rev. Lett. 103 (2009) 152302 Zapp, Stachel, Wiedemann, JHEP 1107 (2011) 118

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Modelling the medium

geometry: overlap, Npart, Ncoll etc. from Glauber model

Eskola, Kajantie, Lindfors, Nucl. Phys. B 323 (1989)

EOS: ideal relativistic quark-gluon gas ⇒ n =∝ T 3 & ǫ =∝ T 4 expansion: boost-invariant longitudinal expansion T(τ) ∝ τ−1/3 ⇒ n(τ) ∝ τ−1 & ǫ(τ) ∝ τ−4/3 (τ = √ t2 − z2)

Bjorken, Phys. Rev. D 27 (1983)

local energy density: ǫ(x, y, τ) ∝ Ncoll(x, y) · τ−4/3 jet production: pQCD matrix elements (PYTHIA) + distribution according to Ncoll(x, y)

4 8 12

8

2 4 6 8

2
6 -4

6

8
6 -2024

x [ f m ] y [fm] ǫ [GeV/fm3] 8

4

t = 4 fm/c 4 8 12

8

2 4 6 8

2
6 -4

6

8
6 -2024

x [ f m ] y [fm] ǫ [GeV/fm3] 8

4

t = 2 fm/c

4

4 8 12

8

2 4 6 8

2
6 -4

6

8
6 -2024

x [ f m ] y [fm] ǫ [GeV/fm3] 8 t = 1 fm/c b = 4 fm z = 0

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL validation

π0

b b b b b b b b b b b b b b b b b b b b b b b b b

PHENIX p+p data

b

JEWEL+PYTHIA 10−9 10−8 10−7 10−6 10−5 10−4 10−3 10−2 10−1 1 10 1 1/(2π) d2N/(p⊥dydp⊥) [GeV−2] 2 4 6 8 10 12 14 16 18 0.6 0.8 1 1.2 1.4 p⊥ [GeV] MC/data

◮ π0 p⊥-spectrum at √s = 200 A GeV

PHENIX, Phys. Rev. D 76 (2007) 051106

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL hadron suppression at RHIC

0.2 0.4 0.6 0.8 1 5 10 15 20 25 RAA pt [GeV] π0 PHENIX data, 0-10% centrality JEWEL+PYTHIA

◮ π0 suppression at √s = 200 A GeV ◮ grey band: variation of µD by ±10 %

Ti = 350 MeV, τi = 0.8 fm, Tc = 165 MeV

PHENIX, Phys. Rev. Lett. 101 (2008) 232301

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

JEWEL hadron suppression at the LHC

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 10 100 1000 RAA pt [GeV] charged hadrons CMS preliminary data, 0-5% centrality ALICE preliminary data, 0-5% centrality JEWEL+PYTHIA

◮ charged hadron suppression at √s = 2.76 A TeV ◮ interesting behaviour at very high p⊥

Ti = 530 MeV, τi = 0.5 fm, Tc = 165 MeV, scaled using multiplicity

CMS, Eur. Phys. J. C (2012) 72:1945; ALICE J. Phys. G G 38 (2011) 124014

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

An interesting piece of kinematics

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 200 300 400 500 600 700 800 900 RAA pt/E [GeV] RAA vs. E w/ nuclear pdf

SLIDE 40

Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

An interesting piece of kinematics

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 200 300 400 500 600 700 800 900 RAA pt/E [GeV] RAA vs. E w/ nuclear pdf RAA vs. E w/o nuclear pdf

◮ no energy loss at very high p⊥

SLIDE 41

Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

An interesting piece of kinematics

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 200 300 400 500 600 700 800 900 RAA pt/E [GeV] RAA vs. E w/ nuclear pdf RAA vs. E w/o nuclear pdf RAA vs. pT w/o nuclear pdf

◮ no energy loss at very high p⊥ ◮ conversion of longitudinal into transverse momentum

due to multiple scattering

SLIDE 42

Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

An interesting piece of kinematics

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 200 300 400 500 600 700 800 900 RAA pt/E [GeV] RAA vs. E w/ nuclear pdf RAA vs. E w/o nuclear pdf RAA vs. pT w/o nuclear pdf

◮ no energy loss at very high p⊥ ◮ conversion of longitudinal into transverse momentum

due to multiple scattering

◮ only possible in non-eikonal kinematics

SLIDE 43

Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Outlook: reconstructed jets (preliminary)

b b b b b b b b b b b b b b

ATLAS p+p data

b

JEWEL+PYTHIA 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.5 1 1.5 2 2.5 3 3.5 4 4.5 dijet asymmetry in p+p (7 TeV) AJ 1/NevtdN/dAJ

b b b b b b b b b b

ATLAS p+p data

b

JEWEL+PYTHIA 1.6 1.8 2 2.2 2.4 2.6 2.8 3 10−2 10−1 1 dijet azimuthal decorrelation in p+p (7 TeV) ∆φ 1/NevtdN/d∆φ

b b b b b b b b b b b b b b

ATLAS Pb+Pb data

b

JEWEL+PYTHIA 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.5 1 1.5 2 2.5 dijet asymmetry in Pb+Pb AJ 1/NevtdN/dAJ

b b b b b b b b b b b b b b b b

JEWEL+PYTHIA ATLAS Pb+Pb data

b

1.6 1.8 2 2.2 2.4 2.6 2.8 3 10−1 1 dijet azimuthal decorrelation in Pb+Pb ∆φ 1/NevtdN/d∆φ

◮ p+p baseline missing underlying event ◮ Pb+Pb not bad ◮ need to understand possible artefacts of background

subtraction in Pb+Pb

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Jet Quenching in the light of perturbative QCD Korinna Zapp Experimental findings Analytical approach MC approach Conclusions

Conclusions

◮ jet quenching is there, it is big and it is interesting ◮ analytical approaches: may give theoretical insight, but

not suitable for describing data

◮ JEWEL: MC model for jet quenching based on

perturbative QCD in general kinematics

◮ consistent with all analytically known limiting cases ◮ first confrontation with data looks very promising ◮ next: go for exclusive observables & jets

vacuum

Q2-evolution elastic scattering without Q2-evolution without Q2-evolution LPM-suppression inelastic scattering

JEWEL