Recent Results on Soft Probes of the Quark-Gluon Plasma from the ATLAS Experiment at the LHC

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Recent Results on Soft Probes of the Quark-Gluon Plasma from the ATLAS Experiment at the LHC

Mariusz Przybycień

AGH University of Science and Technology, Krakow, Poland

(on behalf of the ATLAS Collaboration)

M. Przybycień (AGH UST) Soft Probes of QGP with ATLAS 4 July 2014 1 / 17

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Soft probes of QGP - results from Pb+Pb and p+Pb

IRecent results from lead-lead collisions:

• Collective flow with higher-order cumulants in lead-lead collisions at√

s_NN= 2.76 TeV with the ATLAS detector at the LHC, ATLAS-CONF-2014-027

• Measurement of event-plane correlations in√

s_NN= 2.76 TeV lead-lead collisions with the ATLAS detector,arXiv:1403.0489

• Measurement of the centrality and pseudorapidity dependence of the integrated elliptic flow in lead-lead collisions at√

sNN= 2.76 TeV with the ATLAS detector,arXiv:1405.3936

• Measurement of the correlation between elliptic flow and higher-order flow harmonics in lead-lead collisions at√

sNN= 2.76 TeV, ATLAS-CONF-2014-022

IRecent results from proton-lead collisions:

• Measurement of long-range pseudorapidity correlations and azimuthal harmonics in√

s_NN= 5.02 TeV proton-lead collisions with the ATLAS detector,

ATLAS-CONF-2014-021

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The ATLAS detector

Detector coverage:

Inner Detector (ID):

|η|<2.5

Calorimeter (CAL):

|η|<3.2 (EM)

|η|<4.9 (HAD) 3.2<|η|<4.9 (FCal) Zero Degree Cal. (ZDC):

|η|>8.3 @z=±140 m MB Trig. Scint. (MBTS):

2.1<|η|<3.9

Magnetic fields:

•2T solenoid field in ID

•Toroidal field in MS

Identification of minimum-bias Pb+Pb collisions:

measurement of spectator neutrons in Zero Degree Calorimeters (ZDCs) and charged particles (pulse hight and arrival times) in Minimum Bias Trigger Scintillators (MBTS).

Pb+Pb data (2010):√

sNN= 2.76 TeV,L= 7µb⁻¹. p+Pb data (2013):√

sNN= 5.02 TeV,L= 28 nb⁻¹.

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Centrality determination in Pb+Pb and p+Pb

ICentrality is measured using forward calorimeters (3.2

η

<|η|<4.9):

Iin Pb+Pb use sum of ETon both sides,

Iin p+Pb use sum of ETon Pb-going side only,

Ifor Pb+Pb use Glauber MC for geometry,

Ifor p+Pb use both Glauber and Glauber-Gribov color fluctuation model (PLB 633: 245 (2006)).

IAverage number of participants (N_part) for each centrality bin resulting from fits to the measured E_T distribution for p+Pb.

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Theoretical framework

Final state momentum anisotropy is studied via Fourier decomposition of the azimuthal angle:

Ed³N dp³ = 1

p_T d³N

dφdp_Tdy = 1 2πp_T

E p

d²N

dp_Tdη 1 + 2

∞

X

n=1

vncosn(φ−Φn)

!

Φ_n - azimuthal angle of the n-th order symmetry plane of the initial geometry, vn≡ he^in(φ−Φⁿ⁾i=hcosn(φ−Φn)i- magnitude of the n-th flow harmonics.

IEvent plane method:

Φn= 1 narc tg

PE_Ti^towwisin (nφi) PE_Ti^toww_icos (nφ_i) v_n =hcos [n(φ^P,N_i −Φ^N,P_n )]i/

q

hcos [n(Φ^N_n −Φ^P_n)]i

ICumulant method:

hcorrn{2k}i=hhe^in(φ¹^+...+φ^k^−φ^k+1^−...−φ^2k⁾ii=hvn{2k}^2ki cn{4}=hcorrn{4}i −2hcorrn{2}i²

vn{4}(pT, η) =−dn{4}/^3/4p

−cn{4}

z P

y

lab

x

T lab

particle outgoing

φ reaction plane

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Flow harmonics with multiparticle cumulants in Pb+Pb

I2k-particle cumulants are insensitive to lower order correlations (<2k) - non-flow efects (i.e. not related to the initial geomentry) are eliminated.

IGenerating function is used to obtain 2k-particle correlations and cumulants (N.Borghini et al., arXiv:nucl-ex/0110016)

ITransverse momentum dependence of flow harmonics:

0 5 10 15 20

2v

0 0.1 0.2^ATLAS Preliminary

= 2.76 TeV sNN Pb-Pb

b-1 µ

≈ 7 Lint

| < 0.8 η

| 5-10%

0 5 10 15 20

0 0.1

0.2 v₂{4} ATLAS

CMS 2{4}

v 15-20%

0 5 10 15 20

0 0.1

0.2 ^25-30%

0 5 10 15 20

0 0.1

0.2 ^35-40%

[GeV]

pT

0 5 10 15 20

0 0.1

0.2 ^40-50%

0 5 10 15 20

2v

0 0.1 0.2ATLAS Preliminary

b-1 µ

≈ 7 Lint

| < 0.8 η

| 5-10%

0 5 10 15 20

0 0.1

0.2 v₂{4} ATLAS

ALICE 2{4}

v 10-20%

0 5 10 15 20

0 0.1 0.2

20-30%

0 5 10 15 20

0 0.1 0.2

30-40%

[GeV]

pT

0 5 10 15 20

0 0.1 0.2

40-50%

5 10 15 20

3v

0 0.05 0.1

{EP}

v3 3{2}

v {4}

v3 ATLAS Preliminary

= 2.76 TeV sNN Pb+Pb

| < 2.5 η -1, | µb

≈ 7 Lint

0-25%

[GeV]

pT

5 10 15 20

0 0.05 0.1

25-60%

[GeV]

pT

5 10 15 20

4v

0 0.05 0.1

4{EP}

v 4{2}

v 4{4}

v ATLAS Preliminary

| < 2.5 η -1, | µb

≈ 7 Lint

0-25%

•strong reduction of vn by using more than 2-particle correlations, in general: vn{2}>vn{EP}>vn{4} ≈vn{6} ≈vn{8}

•good agreement of v2{4} with ALICE and CMS,

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Flow harmonics with multiparticle cumulants in Pb+Pb

IPseudorapidity dependence of flow harmonics:

-2 -1 0 1 2 η

3v

0 0.02 0.04 0.06

3{EP}

v

3{2}

v

3{4}

< 20 GeV , 0.5 < pT b-1 µ

≈ 7 Lint

0-60%

-2 -1 0 1 2 η

4v

0 0.01 0.02 0.03

4{EP}

v

4{2}

v

4{4}

< 20 GeV , 0.5 < pT b-1 µ

≈ 7 Lint

0-25%

•integrated over 0.5< pT<20 GeV,

•vn{2}, vn{EP}>vn{2k} for k >1,

•no strong dependence on pseudorapidity,

ICentrality dependence of flow harmonics:

•integrated overpTandη,

•vn{2}>vn{EP} vn{EbyE}>vn{4}

•vn{EbyE}- ”event by event” fromp(vn) distr.

•large contribution from the 2-particle correlations present in vn{2}are suppressed in vn{EP},

•negative contribution of flow fluctuations to vn{4}.

part〉

〈N

0 50 100 150 200 250 300 350 400

2v

0 0.05 0.1 0.15

2{EP}

v 2{2}

v 2{4}

v {EbyE}

v2

ATLAS Preliminary = 2.76 TeV sNN Pb-Pb

| < 2.5 η | b-1 µ

≈ 7 Lint

< 20 GeV 0.5 < pT

part〉

〈N

0 50 100 150 200 250 300 350 400

3v

0 0.02 0.04

0.06 v₃{EP}

3{2}

v 3{4}

v {EbyE}

b-1 µ

≈ 7 Lint

| < 2.5 η < 20 GeV, | 0.5 < pT

part〉

〈N

0 50 100 150 200 250 300 350 400

4v

0 0.02 0.04 0.06

4{EP}

v 4{2}

v 4{4}

v {EbyE}

b-1 µ

≈ 7 Lint

| < 2.5 η

| < 20 GeV T 0.5 < p

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Event plane correlations in Pb+Pb (arXiv:1403.0489)

ICorrelation between Φ_n and Φ_mis described by the differential event yield:

dN_evts

d(k(Φn−Φm))∝1 + 2

∞

X

j=1

V^j_n,mcosjk(Φ_n−Φ_m)

V_n,m^j =hcosjk(Φn−Φm)i

•can be generalized for three or more event planes,

•use EP or SP method (PR C87, 044907 (2013)),

•poor agreemnet with Glauber model,

•good agreements with AMPT (PR C72, 064901 (2005))

part〉

〈N

0 100 200 300 400

〉)4Φ-2Φcos4(〈

0 0.5 1

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

AMPT

〉w Φ) Σ

〈cos(

AMPT

〉 Φ) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)6Φ-3Φcos6(〈

0 0.5 1

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

AMPT

〉w Φ) Σ

〈cos(

AMPT

〉 Φ) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)4Φ-2Φcos4(〈

-0.5 0 0.5 1 1.5

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

Glauber

〉w Φ*) Σ

〈cos(

Glauber

〉 Φ*) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)6Φ-3Φcos6(〈

-0.5 0 0.5

1 ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

Glauber

〉w Φ*) Σ

〈cos(

Glauber

〉 Φ*) Σ

〈cos(

⇒significant non-linear flow contributions to higher order harmonics

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Event plane correlations in Pb+Pb (arXiv:1403.0489)

IComparison of three plane correlators:

part〉

〈N

0 100 200 300 400

〉)5Φ-53Φ+32Φcos(2〈

0 1

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

Glauber

〉w Φ*) cos(Σ

〈 Glauber

〉 Φ*) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)6Φ-64Φ+42Φcos(2〈

0 1

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

Glauber

〉w Φ*) cos(Σ

〈 Glauber

〉 Φ*) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)4Φ+43Φ-62Φcos(2〈

-0.2 0 0.2

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

Glauber

〉w Φ*) cos(Σ

〈 Glauber

〉 Φ*) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)5Φ+53Φ+32Φcos(-8〈

-0.2 0 0.2 0.4ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data )〉 Φ cos(Σ

〈 Glauber

〉w Φ*) Σ

〈cos(

Glauber

〉 Φ*) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)6Φ+64Φ+42Φcos(-10〈

-0.5 0 0.5 1

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data )〉 Φ cos(Σ

〈 Glauber

〉w Φ*) Σ

〈cos(

Glauber

〉 Φ*) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)4Φ+43Φ+62Φcos(-10〈

0 0.05 0.1 0.15

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data )〉 Φ cos(Σ

〈 Glauber

〉w Φ*) Σ

〈cos(

Glauber

〉 Φ*) Σ

〈cos(

Igood agreement with AMPT model, poor agreement with Glauber model.

part〉

〈N

0 100 200 300 400

〉)5Φ-53Φ+32Φcos(2〈

0 0.5 1 1.5 ATLASPb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

AMPT

〉w Φ) Σ

〈cos(

AMPT

〉 Φ) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)6Φ-64Φ+42Φcos(2〈

0 0.5 1 1.5 ATLASPb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

AMPT

〉w Φ) Σ

〈cos(

AMPT

〉 Φ) Σ

〈cos(

part〉

〈N

0 100 200 300 400

〉)4Φ+43Φ-62Φcos(2〈

-0.2 -0.1 0 0.1 0.2ATLASPb+Pb

=2.76 TeV sNN

b-1 µ = 7 Lint

data

〉w Φ) Σ

〈cos(

data

〉 Φ) Σ

〈cos(

AMPT

〉w Φ) Σ

〈cos(

AMPT

〉 Φ) Σ

〈cos(

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Integrated eliptic flow in Pb+Pb (arXiv:1405.3936)

ICentrality dependence of integrated v2:

0.2 0.4

2v

0.02 0.04 0.06 0.08 0.1 0.12 method:

TKT PXT IDT

centrality:

0-10%

|<1 η

|

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

10-20%

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

20-30%

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

30-40%

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

40-50%

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

50-60%

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

60-70%

[GeV]

pT,0

0.2 0.4

0.02 0.04 0.06 0.08 0.1 0.12

70-80%

ATLAS

=2.76 TeV sNN

Pb+Pb

b-1

µ = 0.5 IDT & PXT: Lint

b-1

µ = 1 TKT: Lint

IThree tracking techniques used to minimize the lowp_Tlimit (p_T,0):

•IDT - default tracking,pT>0.5 GeV

•PXT - lowpTtracking,pT>0.1 GeV

•TKT - field off data,pT>0.07 GeV (estimated with MC)

IConsistent results with different tracking techniques for matchingpT,0.

INo need to extrapolate top_T,0= 0 to obtain reliable estimate of v2

integrated over whole kinematic range inp_T.

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Integrated eliptic flow in Pb+Pb (arXiv:1405.3936)

ICentrality dependence of integrated v2:

•clear dependence onpT,0,

•integrated elliptic flow increases with centrality, reaching maximum for mid-central collisions (40-50%) and then decreases for the more central collisions.

•good agreement with CMS results (Phys. Rev. C87, 014902 (2013))

IPseudorapidity dependence of integrated v2:

•very weak dependence on pseudorapidity

•good agreement with CMS measurement.

Centrality [%]

0 10 20 30 40 50 60 70 80

2v

0 0.02 0.04 0.06 0.08 0.1 0.12

|<1 η

>0.07 GeV, | T ATLAS TKT p

|<1 η

<5 GeV, | ATLAS PXT 0.1<pT

|<1 η

<5 GeV, | ATLAS PXT 0.3<pT

|<0.8 η

<3 GeV, | CMS 0.3<pT

ATLAS Pb+Pb

=2.76 TeV sNN

b-1 µ = 0.5 PXT method: Lint

b-1 µ = 1 TKT method: Lint

-2 -1 0 1 2 η

2v

0 0.02 0.04 0.06 0.08 0.1 0.12

b-1 µ = 1

>0.07 GeV, Lint ATLAS TKT method pT

b-1 µ = 0.5

>0.1 GeV, Lint ATLAS PXT method pT

b-1 µ = 0.5

>0.2 GeV, Lint ATLAS PXT method pT

b-1 µ = 0.5

>0.3 GeV, Lint T ATLAS PXT method p

>0.3 GeV CMS pT

ATLAS Pb+Pb s_NN=2.76 TeV

cenrtality: 40-50%

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Correlations between v

2

and higher order flow harmonics

IStudy correlations between v2 and vn (n= 2,3,4,5) for various centrality intervals using two-particle correlation function with|∆η|>2:

•boomerang-like structure seen in all correlation plots:

- reflects the characteristic centrality dependence of v2

- is consistent with hydrodynamic predictions of stronger viscous-damping effects for v3than v2 forpT<3 GeV or for 0−50% centrality interval,

- significant non-linear contributions to v4from v2 make the boomerang-like structure less pronounced in v2−v4

correlations.

v2

0 0.05 0.1 0.15

5v

0 0.005 0.01

ATLAS Prelim.

=2.76 TeV sNN

b-1

µ = 7

Lint |∆η|>2, Pb+Pb < 2 GeV 0.5 < pT

Centrality 0-60%

Central

Peripheral

v

} < 2 GeV 0.5 < pT 2 { v

0 0.05 0.1 0.15

} < 3 GeVT2 < p {2v

0 0.1 0.2 0.3

ATLAS Preliminary

=2.76 TeV sNN

b-1 µ = 7 Lint

|>2, Pb+Pb η

∆

| Centrality 0-70%

Central

Peripheral

v2

0 0.05 0.1 0.15

3v

0 0.02 0.04

=2.76 TeV sNN

b-1 µ = 7

Lint |∆η|>2, Pb+Pb < 2 GeV 0.5 < pT Centrality 0-70%

Central Peripheral

v2

0 0.05 0.1 0.15

4v

0 0.01 0.02

0.03 ATLAS Preliminary

=2.76 TeV sNN

b-1 µ = 7

Lint |∆η|>2, Pb+Pb < 2 GeV 0.5 < pT Centrality 0-65%

Central

Peripheral

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Correlations between v

2

and higher order flow harmonics

IEvents within each centrality are subdivided intoq2 (flow vector) intervals:

~ q2= 1

Pwi

X[wicos 2φi],X

[wisin 2φi]

− h~q2ievts

wherewi=E^{F Cal}_T,i

IFix initial geometry (system size) and vary elipticity:

FCal q2

0 0.05 0.1 0.15

2/dqevtdNevt1/N

10-2 10-1 1 10

ATLASPreliminary

=2.76 TeV sNN

b-1 µ = 7 Lint

Pb+Pb Centrality 25-26%

95-100% 90-95% 80-90% 70-80% 60-70% 50-60%40-50%30-40% 20-30% 10-20% 7.5-10%5-7.5%2.5-5% 0-2.5%

} < 2 GeV T 0.5 < p 2 { v

0 0.05 0.1 0.15

} < 4 GeVT3 < p {2v

0 0.1 0.2

=2.76 TeV sNN

b-1 µ = 7 Lint Pb+Pb

|>2 η

∆

|

selection Centrality 0-70%, no q2

Centrality intervals selection:

with q2 0-5%

10-15%

20-25%

30-35%

40-45%

50-55%

60-65%

Linear correlation within given centrality⇒viscous damping controlled by system size, not shape.

v2

0 0.05 0.1 0.15

3v

0.02 0.03 0.04 0.05 0.06

=2.76 TeV sNN

|>2 η

∆ < 2 GeV, | 0.5 < pT

with q2 0-5%

10-15%

20-25%

30-35%

40-45%

50-55%

60-65%

Clear anti-correlation, mostly initial geometry effect (AMPT calculations).

v2

0 0.05 0.1 0.15

4v

0 0.01 0.02

=2.76 TeV sNN

< 2 GeV 0.5 < pT

|>2 η

∆

|

with q2 0-5%

10-15%

20-25%

30-35%

40-45%

50-55%

60-65%

Quadratic rise from non-linear coupling to v²₂, initial geometry does not work.

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Flow non-linearity in v

4

and v

5

Iv4–v2 correlation for fixed centrality bin: v4eî4Φ⁴ =c0eîΦ^?⁴ +c1 v2eî2Φ²²

v2

0 0.05 0.1 0.15

4v

0.012 0.014 0.016 0.018 0-5%

ATLAS Prelim.

=2.76 TeV sNN

b-1

µ = 7 Lint

Pb+Pb

|>2 η

∆

| < 2 GeV 0.5 < pT

v2

0 0.05 0.1 0.15

4v

0.012 0.014 0.016 0.018 10-15%

v2

0 0.05 0.1 0.15

4v

0.015 0.02 0.025

15-20%

data )2 2 v2 1 2+(c c0 4= Fit v Glauber MC-KLN

v2

0 0.05 0.1 0.15

4v

0.02 0.03

30-35%

•Fit to v4=p

c²₀+c²₁v₂⁴to separate linear and non-linear component:

2 2

Npart

0 100 200 300 400

0c

0 0.005 0.01 0.015

=2.76 TeV sNN

, Pb+Pb b-1

µ = 7 Lint

|>2 η

∆

| < 2 GeV 0.5 < pT

Npart

0 100 200 300 400

1c

1 1.5

=2.76 TeV sNN

,Pb+Pb b-1

µ = 7 Lint

|>2 η

|∆ < 2 GeV 0.5 < pT

• Extract linear and non-linear terms v^L₄ =c₀, v₄^NL=p

v₄²−c²₀

as a function of centrality. ^N^part

0 100 200 300 400

4v

0 0.01 0.02

=2.76 TeV sNN

|>2 η

∆

| < 2 GeV 0.5 < pT Inclusive Linear non-Linear

EP Linear EP non-Linear

INon-linear behaviour observed also in v5–v2 correlation, fit v5=p

c²₀+ (c1v2v3)².

(15)

Long range correlations in p+Pb collisions

IMeasurement of two-particle correlation function in p-Pb collisions:

•low-activity evt. - yield function contains mainly short-range correlations,

•high-activity evt. - also important contribution from long-range ‘ridge’ correl.

•to obtain long-range component, estimate first short-range component from peripheral events and then subtract,

∆φ 0 2 4

∆η )η∆,φ∆Y( _1.65

1.7 1.75

-4 -2 0 2 4

≥ 220

rec

Nch (a)

-4 -2 0 2 4

∆φ 0 2 4

∆η )η∆,φ∆(subY^1.65

1.7 1.75

-4 -2 0 2 4

≥ 220

rec

Nch (b)

•extract flow harmonics from the correlation function for high activity events:

[GeV]

a T p

0 5 10

nv

-0.05 0 0.05 0.1 0.15

unsub v2 v2

| < 5 η

∆ < 3 GeV, 2 < | b 1 < pT

≥ 220 rec Nch

=5.02 TeV sNN

28 nb-1

≈ Lint

p+Pb

[GeV]

a T p

0 5 10

unsub v3 v3

[GeV]

a T p

0 5 10

unsub v4 v4

(16)

Compare flow harmonics in p+Pb and Pb+Pb collisions

ISignifficantly larger v₂ and v₄in Pb+Pb but comparable magnitudes for v₃, (v₂and v₄ are coupled v₄=p

c²₀+c²₁v⁴₂).

ICompare v_n(p_T)_p+Pbwith v_n(p_T/K)_Pb+Pb, (Taney et al. nucl-th/1312.6770)

• p+Pb:hN_chi ≈259±13 Pb+Pb:hN_chi ≈241±43

•K= 1.25 - ratio ofhp_Ti

•v2after scaling thepTaxis differ only by scale factor between the two systems.

•This suggests that long-range ridge correlations in high multiplicity p+Pb collisions and peripheral Pb+Pb collisions are driven by similar dynamics.

[GeV]

pT

0 5 10

2v

0 0.05 0.1 0.15 0.2

<260 rec Nch

≤ p+Pb 220 Pb+Pb Centrality 55-60%

[GeV]

pT

0 5 10

×0.66 1.25) T/

2(p v Pb+Pb Centrality 55-60%,

[GeV]

pT

0 5 10

3v

0 0.05 0.1

<260 rec Nch

[GeV]

pT

0 5 10

ATLAS Preliminary 1.25) T/

[GeV]

pT

0 5 10

4v

0 0.02 0.04 0.06 0.08

<260 rec Nch

[GeV]

pT

0 5 10

×0.66 1.25) T/

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Summary

ATLAS has provided several new results on soft probes of QGP:

flow coefficients vnwere obtained with higher order cumulants,

the elliptic flow obtained with four-particle cumulants provides a measure of v2

with non-flow correlations strongly suppressed,

event-plane correlations involving two and three event planes of different order have been measured as a function of centrality, good description by the Glauber model including the final state collective dynamics,

thepTintegrated elliptic flow measured with different methods shows clear dependence onpT,0,

correlations between elliptic flow in differentpTranges show non-trivial centrality dependence, while they are found to be linear within narrow centrality intervals, which indicates that viscous effects are controlled by the system size, not its shape, correlations of v2with higher order flow harmonics vn, n= 4,5, disagree with predictions based on initial geometry models, but are consistent with combined contributions of linear and non-linear terms,

long range correlations and flow harmonics have been studied in p+Pb collisions.

More on https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HeavyIonsPublicResults Thank you for your attention!

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Backup slides

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Backup slide

Flow harmonics with multi-particle cumulants in Pb+Pb (ATLAS-CONF-2014-27):

[GeV]

T p

5 10 15 20

2v

0 0.1 0.2

2{EP}

v 2{2}

v 2{4}

v 2{6}

v 2{8}

v

0-2%

[GeV]

T p

5 10 15 20

2v

0 0.1 0.2

2-5%

[GeV]

T p

5 10 15 20

2v

0 0.1 0.2

5-10%

5 10 15 20

0 0.1 0.2

10-15%

[GeV]

pT

5 10 15 20

2v

0 0.1 0.2

15-20%

[GeV]

pT

5 10 15 20

2v

0 0.1 0.2

20-25%

5 10 15 20

0 0.1 0.2

25-30%

[GeV]

T p

5 10 15 20

2v

0 0.1 0.2

30-35%

[GeV]

T p

5 10 15 20

2v

0 0.1 0.2

35-40%

5 10 15 20

0 0.1 0.2

40-45%

[GeV]

T

5 10 15 p20

2v

0 0.1 0.2

45-50%

[GeV]

T

5 10 15 p 20

2v

0 0.1 0.2

50-55%

5 10 15 20

0 0.1 0.2 0.3 0.4 0.5 0.6

0.7 _55-60%

5 10 15 20

0 0.1 0.2 0.3 0.4 0.5 0.6

0.7 60-80%

[GeV]

pT

5 10 15 20

0 0.1 0.2 0.3 0.4 0.5 0.6

0.7 ATLAS Preliminary = 2.76 TeV sNN

Pb+Pb b-1

µ

≈ 7 Lint

| < 2.5 η

|