Recent Results on Hard Probes of the Quark-Gluon Plasma with the - - PowerPoint PPT Presentation

SLIDE 1

Recent Results on Hard Probes of the Quark-Gluon Plasma with the ATLAS Experiment at the LHC

Tom´ aˇ s Kosek

for the ATLAS collaboration

53rd International Winter Meeting

• n Nuclear Physics

26-30 January 2015 IPNP, Charles University in Prague

Tom´ aˇ s Kosek 29 January 2015 1 / 21

SLIDE 2

Motivation

The main goal of the presented measurements is to study properties

• f the strongly coupled medium created in Heavy-ion (HI) collisions

Hard probes are ideal tools for these studies

◮ created in the early stages of the collision ◮ relatively low background from the underlying event Tom´ aˇ s Kosek 29 January 2015 2 / 21

SLIDE 3

ATLAS experiment

ATLAS is multi-purpose detector well capable of measuring heavy-ion collisions Excellent tracking performance within |η| < 2.5. Combination of silicon pixel and strip detectors and transition radiation tracker. Powerful calorimeter system with fine segmentation with η coverage up to |η| < 4.9

Tom´ aˇ s Kosek 29 January 2015 3 / 21

SLIDE 4

More about calorimetry

∆ ϕ = . 2 4 5 ∆ η = . 2 5 3 7 . 5 m m / 8 = 4 . 6 9 m m

• ∆

η = . 3 1 ∆ ϕ = . 2 4 5 x 4

• 3

6 . 8 m m x 4

• =

1 4 7 . 3 m m T r i g g e r T

• w

e r T r i g g e r T

• w

e r ∆ ϕ = . 9 8 2 ∆ η = . 1 16X0 4.3X0 2X0 1 5 m m 4 7 m m η ϕ

η = 0

Strip cells in Layer 1 Square cells in Layer 2 1.7X0 Cells in Layer 3 ∆ϕ× ∆η = 0.0245× 0.05

Calorimetry system is composed of electromagnetic, hadronic and liquid-argon (LAr) forward calorimeters High granularity LAr electromagnetic calorimeter covers range of |η| < 3.2 and is composed of barrel and end-cap modules EM calorimeter is backed by hadronic calorimeter Allows for precise measurement of photons, electrons and jets Forward calorimeters are located in the range 3.1 < |η| < 4.9, used for centrality bin selection

Tom´ aˇ s Kosek 29 January 2015 4 / 21

SLIDE 5

Centrality in Pb+Pb collisions

Centrality expresses measure of overlap of two colliding nuclei Is closely related to the average number of participant nucleons and number of binary inelastic collisions Centrality determined by the sum of ET deposited in the FCAL calorimeter (3.1 < |η| < 4.9) Events divided into successive percentiles of the E FCal

T

Tom´ aˇ s Kosek 29 January 2015 5 / 21

SLIDE 6

EW probes

Since EW bosons don’t interact strongly, they aren’t influenced by the medium We can look at the EW boson+jet events - is pT balanced? Or we can test modification of the PDF’s caused by the nuclear effects

Tom´ aˇ s Kosek 29 January 2015 6 / 21

SLIDE 7

W bosons (1)

arXiv:1408.4674

|

l

η | 0.5 1 1.5 2 2.5

〉

coll

N 〈

9

10

events

N 1 η d dN

1 2 3 4 5 6 7 8 9 10

Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb

ν

+

l →

+

W

• 1

0.14-0.15 nb ≈ Ldt

∫

= 2.76 TeV

NN

s Pb+Pb

ATLAS |

l

η | 0.5 1 1.5 2 2.5

〉

coll

N 〈

9

10

events

N 1 η d dN

1 2 3 4 5 6 7 8 9 10

Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb

ν

• l

→

• W
• 1

0.14-0.15 nb ≈ Ldt

∫

= 2.76 TeV

NN

s Pb+Pb

ATLAS

Differential production yield per binary collision for W + and W − integrated over centralities and compared to theoretical predicitons

Tom´ aˇ s Kosek 29 January 2015 7 / 21

SLIDE 8

W bosons (2)

〉

part

N 〈 50 100 150 200 250 300 350 400

events

N

fiducial

N 〉

coll

N 〈

9

10

5 10 15 20 25 30 35 40

Data

±

W+ W- W POWHEG CT10

±

W+ W- W

• 1

0.14-0.15 nb ≈ Ldt

∫

= 2.76 TeV

NN

s Pb+Pb

ATLAS |

l

η | 0.5 1 1.5 2 2.5

l

Lepton Charge Asymmetry A

• 0.4
• 0.3
• 0.2
• 0.1

0.1 0.2 0.3 0.4

Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb Data 2011 POWHEG CT10 Pb+Pb CT10+EPS09 Pb+Pb

• 1

0.14-0.15 nb ≈ Ldt

∫

= 2.76 TeV

NN

s Pb+Pb

ATLAS

W production yield per binary collision doesn’t show any dependence

• n Npart and is consistent with POWHEG prediction

Lepton charge asymmetry agrees with theoretical predictions

Tom´ aˇ s Kosek 29 January 2015 8 / 21

SLIDE 9

Photons (1)

ATLAS-CONF-2014-026

[GeV]

T

p photon 30 40 50

2

10

2

10 × 2 [pb/GeV]

AA

T )/

T

p /d

γ

)(dN

evt

(1/N

• 2

10 1

2

10

4

10

6

10

7

10

Preliminary ATLAS =2.76 TeV

NN

s Pb+Pb |<1.37 η | JETPHOX 1.3 (R=0.3) < 6 GeV

T,iso

E

3

10 × Data 0-10%

2

10 × Data 10-20%

1

10 × Data 20-40% 10 × Data 40-80%

[GeV]

T

p photon 30 40 50 60 70

2

10 [pb/GeV]

AA

T )/

T

p /d

γ

(dN

• 2

10 1

2

10

4

10

6

10

7

10

Preliminary ATLAS =2.76 TeV

NN

s Pb+Pb |<2.37 η 1.52<| JETPHOX 1.3 (R=0.3) < 6 GeV

T,iso

E

3

10 × Data 0-10%

2

10 × Data 10-20%

1

10 × Data 20-40% 10 × Data 40-80%

Fully corrected yields of prompt photons in four centrality intervals as a function of pT Compared to JETPHOX calculations

Tom´ aˇ s Kosek 29 January 2015 9 / 21

SLIDE 10

Photons (2)

[GeV]

T

p photon

2

10

) pp Ratio to JETPHOX (

0.5 1 1.5 2 |<2.37 η 40-80%, 1.52<|

[GeV]

T

p photon

2

10 0.5 1 1.5 2 |<2.37 η 20-40%, 1.52<|

[GeV]

T

p photon

2

10 0.5 1 1.5 2 |<2.37 η 10-20%, 1.52<|

[GeV]

T

p photon

2

10 0.5 1 1.5 2 |<2.37 η 0-10%, 1.52<|

) pp Ratio to JETPHOX (

0.5 1 1.5 2 |<1.37 η 40-80%, | 0.5 1 1.5 2

JETPHOX PDF+scale err. pp JETPHOX Pb+Pb/ & err. pp JETPHOX EPS09/

|<1.37 η 20-40%, | 0.5 1 1.5 2 |<1.37 η 10-20%, | 0.5 1 1.5 2

Preliminary ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

= 0.14 nb

int

L

|<1.37 η 0-10%, |

The ratio of the data to the JETPHOX pp prediction Data agree well with JETPHOX predictions in all centrality and η regions

Tom´ aˇ s Kosek 29 January 2015 10 / 21

SLIDE 11

Jets

Partons from the hard scattering have to traverse through the deconfined medium Do we observe suppression of jet yields or modification of fragmentation functions? Is production of the associated jets influenced by the medium? We can compare to pp data at the same energy or look at differences between central and peripheral collisions

Tom´ aˇ s Kosek 29 January 2015 11 / 21

SLIDE 12

Jet spectra

arXiv:1411.2357

[GeV]

T

p [ nb/GeV ] y d

T

p d σ

2

d

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 1 10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9

10

10

10

11

10 40 60 100 200 400

)

8

10 × | < 2.1 ( y | )

6

10 × | < 0.3 ( y | )

4

10 × | < 0.8 ( y | ≤ 0.3 )

2

10 × | < 1.2 ( y | ≤ 0.8 ) 10 × | < 2.1 ( y | ≤ 1.2

ATLAS

= 2.76 TeV s =0.4, R

t

k anti-

• 1

data, 4.0 pb pp 2013 [ nb/GeV ] y d

T

p d

jet

N

2

d

evt

N 1 〉

AA

T 〈 1

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 1 10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9

10

10

10

11

10

[GeV]

T

p [ nb/GeV ] y d

T

p d

jet

N

2

d

evt

N 1 〉

AA

T 〈 1

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 1 10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9

10

10

10

11

10 40 60 100 200 400 0 - 10 % )

6

10 × | < 0.3 ( y | )

4

10 × | < 0.8 ( y | ≤ 0.3 )

2

10 × | < 1.2 ( y | ≤ 0.8 ) 10 × | < 2.1 ( y | ≤ 1.2 | < 2.1 y | )

6

10 × 0 - 10 % ( )

4

10 × 20 - 30 % ( )

2

10 × 30 - 40 % ( ) 10 × 60 - 80 % (

ATLAS

= 2.76 TeV

NN

s = 0.4 jets R

t

k anti-

• 1

2011 Pb+Pb data, 0.14 nb

• 1

data, 4.0 pb pp 2013

Differential cross sections for the different rapidity ranges Differential per-event jet yield in Pb+Pb collisions divided by 1/TAA with pp jet cross sections Normalized Pb+Pb yields in central collisions are below the pp yields

Tom´ aˇ s Kosek 29 January 2015 12 / 21

SLIDE 13

Jet RAA

AA

R

0.5 1 | < 2.1 y |

ATLAS

= 0.4 jets R

t

k anti- = 2.76 TeV

NN

s

• 1

2011 Pb+Pb data, 0.14 nb

• 1

data, 4.0 pb pp 2013 AA

R

0.5 1 | < 0.8 y 0.3 < | 0 - 10 % 30 - 40 % 60 - 80 %

[GeV]

T

p

AA

R

0.5 1 40 60 100 200 400 40 60 100 200 400 40 60 100 200 400 | < 2.1 y 1.2 < | 0 - 10 % 30 - 40 % 60 - 80 %

| y |

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 AA

R

0.5 1 0 - 10 % 30 - 40 % 60 - 80 % < 100 GeV

T

p 80 <

ATLAS 〉

part

N 〈

50 100 150 200 250 300 350 400 AA

R

0.5 1 < 100 GeV

T

p 80 < | < 2.1 y | = 0.4 jets R

t

k anti- = 2.76 TeV

NN

s

• 1

2011 Pb+Pb data, 0.14 nb

• 1

data, 4.0 pb pp 2013

Variable that expresses the size of the suppression/enhancement is the so called RAA defined as RAA =

1 Nevt d2Njet dpTdy

• central

TAA

d2σpp

jet

dpTdy

Tom´ aˇ s Kosek 29 January 2015 13 / 21

SLIDE 14

Jet RAA

AA

R

0.5 1 | < 2.1 y |

ATLAS

= 0.4 jets R

t

k anti- = 2.76 TeV

NN

s

• 1

2011 Pb+Pb data, 0.14 nb

• 1

data, 4.0 pb pp 2013 AA

R

0.5 1 | < 0.8 y 0.3 < | 0 - 10 % 30 - 40 % 60 - 80 %

[GeV]

T

p

AA

R

0.5 1 40 60 100 200 400 40 60 100 200 400 40 60 100 200 400 | < 2.1 y 1.2 < | 0 - 10 % 30 - 40 % 60 - 80 %

| y |

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 AA

R

0.5 1 0 - 10 % 30 - 40 % 60 - 80 % < 100 GeV

T

p 80 <

ATLAS 〉

part

N 〈

50 100 150 200 250 300 350 400 AA

R

0.5 1 < 100 GeV

T

p 80 < | < 2.1 y | = 0.4 jets R

t

k anti- = 2.76 TeV

NN

s

• 1

2011 Pb+Pb data, 0.14 nb

• 1

data, 4.0 pb pp 2013

RAA plots clearly show suppression down to ≈ 0.5 for most central collisions Weak dependence of RAA on the pT (slope parameter significantly above zero) No significant dependence on the y observed

Tom´ aˇ s Kosek 29 January 2015 14 / 21

SLIDE 15

Fragmentation functions (1)

PLB 739(2014) 320-342

z

• 1

10 1 D(z)

• 2

10

• 1

10 1 10

2

10

3

10

4

10

6

2 × 0-10%

5

2 × 10-20%

4

2 × 20-30%

3

2 × 30-40%

2

2 × 40-50%

1

2 × 50-60% 60-80% Systematic Uncertainty

ATLAS

=2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb R=0.4

T

anti-k > 100 GeV

jet T

p [GeV]

T

p 10

2

10 )

T

D(p

• 4

10

• 3

10

• 2

10

• 1

10 1 10

2

10

6

2 × 0-10%

5

2 × 10-20%

4

2 × 20-30%

3

2 × 30-40%

2

2 × 40-50%

1

2 × 50-60% 60-80% Systematic Uncertainty

ATLAS

=2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb R=0.4

T

anti-k > 100 GeV

jet T

p

Fragmentation functions D(pT) and D(z) are defined as D(z) = 1 Njet dNch dz D(pT) = 1 Njet dNch dpch

T

Tom´ aˇ s Kosek 29 January 2015 15 / 21

SLIDE 16

Fragmentation functions (2)

z

• 1

10 1

D(z)

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 0-10%/60-80% >100 GeV

jet T

p R=0.4

T

anti-k

ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb z

• 1

10 1

D(z)

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 30-40%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb z

• 1

10 1

D(z)

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Data Systematic Uncertainty

10-20%/60-80%

ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb z

• 1

10 1

D(z)

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 40-50%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb z

• 1

10 1

D(z)

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 20-30%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb z

• 1

10 1

D(z)

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 50-60%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb

Centrality dependence evaluated as the ratio of the all centrality bins to the 60-80% bins Enhanced yield of small and large z fragments for all centralities, suppression of fragments at intermediate z Size of modification gradually decreases from central to peripheral collisions

Tom´ aˇ s Kosek 29 January 2015 16 / 21

SLIDE 17

Fragmentation functions (3)

[GeV]

T

p 10

2

10

)

T

D(p

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 0-10%/60-80% >100 GeV

jet T

p R=0.4

T

anti-k

ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb [GeV]

T

p 10

2

10

)

T

D(p

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 30-40%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb [GeV]

T

p 10

2

10

)

T

D(p

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Data Systematic Uncertainty

10-20%/60-80%

ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb [GeV]

T

p 10

2

10

)

T

D(p

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 40-50%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb [GeV]

T

p 10

2

10

)

T

D(p

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 20-30%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb [GeV]

T

p 10

2

10

)

T

D(p

R

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 50-60%/60-80% ATLAS =2.76 TeV

NN

s Pb+Pb

• 1

0.14 nb

Centrality dependence evaluated as the ratio of the all centrality bins to the 60-80% bins Similar modifications of D(pT) as for D(z)

Tom´ aˇ s Kosek 29 January 2015 17 / 21

SLIDE 18

Nearby jets (1)

ATLAS-CONF-2014-028

The rate of the neighbouring jets that accompany a test jet, R∆R is defined as R∆R = 1 dNtest

jet /dE test T Ntest

jet

• i=1

dNnbr

jet,i

dE test

T

(E test

T

, E nbr

T,min, ∆R)

Tom´ aˇ s Kosek 29 January 2015 18 / 21

SLIDE 19

Nearby jets (2)

ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< >80 GeV

test T

E ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< >80 GeV

test T

E ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< >80 GeV

test T

E ATLAS simulation

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb MC

d=0.4

T

k anti- <1.6 R ∆ 0.8< >80 GeV

test T

E ATLAS simulation

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb MC

d=0.4

T

k anti- <1.6 R ∆ 0.8< >80 GeV

test T

E ATLAS simulation

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb MC

d=0.4

T

k anti- <1.6 R ∆ 0.8< >80 GeV

test T

E ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< > 30 GeV

nbr T

E ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< > 30 GeV

nbr T

E

[GeV]

test T

E

70 100 200 300

R ∆

R

0.05 ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< > 30 GeV

nbr T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >90 GeV

test T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >90 GeV

test T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >90 GeV

test T

E ATLAS simulation Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >90 GeV

test T

E ATLAS simulation Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >90 GeV

test T

E ATLAS simulation Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >90 GeV

test T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< > 45 GeV

nbr T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< > 45 GeV

nbr T

E

[GeV]

test T

E

70 100 200 300

R ∆

R

0.01 0.02 ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< > 45 GeV

nbr T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >110 GeV

test T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >110 GeV

test T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >110 GeV

test T

E ATLAS simulation Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >110 GeV

test T

E ATLAS simulation Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >110 GeV

test T

E ATLAS simulation Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< >110 GeV

test T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< 0-10% 10-20% 20-40% 40-80% > 60 GeV

nbr T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< 0-10% 10-20% 20-40% 40-80% > 60 GeV

nbr T

E

[GeV]

test T

E

70 100 200 300

R ∆

R

0.005 0.01 ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< 0-10% 10-20% 20-40% 40-80% > 60 GeV

nbr T

E

R∆R for R = 0.4 jets evaluated as a function of E test

T

Production of nearby jets is suppressed in central collisions compared to peripheral collisions

Tom´ aˇ s Kosek 29 January 2015 19 / 21

SLIDE 20

Nearby jets (3)

[GeV]

test T

E

70 80 90 100 200 300

R ∆

R

ρ

0.5 1 1.5 ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< > 30 GeV

nbr T

E ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< > 30 GeV

nbr T

E ATLAS

• 1

=0.14 nb

int

L

Preliminary

= 2.76 TeV

NN

s Pb+Pb 2011

d=0.4

T

k anti- <1.6 R ∆ 0.8< > 30 GeV

nbr T

E

[GeV]

test T

E

70 80 100 200 300 ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< > 45 GeV

nbr T

E ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< > 45 GeV

nbr T

E

[GeV]

test T

E

70 80 100 200 300 ATLAS Preliminary d=0.4

T

k anti- <1.6 R ∆ 0.8< 0-10% 10-20% 20-40% > 60 GeV

nbr T

E

The ratio of R∆R for three centrality bins to 40-80% centrality bin Suppression by a factor ≈ 2 in central collisions, no strong ET dependence observed

Tom´ aˇ s Kosek 29 January 2015 20 / 21

SLIDE 21

Conclusions

Measurements of EW probes don’t imply any modification of production yields

◮ W production yield doesn’t show any dependence on Npart ◮ Photon yields agree well with JETPHOX prediction

Jet measurements clearly shows the modification of jet properties due to the interaction with the medium created in the collision

◮ Jet RAAfalls down to 0.5 ◮ RAAdependence on the Npart ◮ Modification of the fragmentation functions Tom´ aˇ s Kosek 29 January 2015 21 / 21