Azimuthally differential pion femtoscopy with respect to second
and third order event planes and deformation of the source shapewith event engineering in Pb-Pb 2.76 TeV
Naoto Tanaka for the ALICE Collaboration
University of Tsukuba, CiRfSE

Motivation
R 2out (fm2)

In heavy ion collisions, initial geometrical fluctuation generates odd orderanisotropies. But the relation between the fluctuation of initial geometry andhigher order anisotropy is not trivial.
Azimuthally differential femtoscopy can help us to access the geometricalsource shape and flow velocity profile at freeze out.
A detailed analysis of azimuthal dependence of HBT radii w.r.t. 3rd order
event plane( Ψ3 ) will provide us the key to the final source triangularity.

4030
2001ϕ50

HBT radii w.r.t Ψ340−0.05

2000.25060

ALICE Preliminary
40

00.5

−0.15
01.5
220 ϕ 30- Ψ 40 (rad)
50
EP, 3

1010Centrality(%)

pair

0.06

0.04- -π π and π π combined

0.02

2030

400.06

2030

40Centrality(%)¨0.35< k T < 0.60 GeV/c0.020.10¨

centrality5-10%0.05−0.020centrality10-20%

102030centrality30-40%
centrality40-50%

00.5

1ϕ

ALI-PREL-116562

pair

1.5
2- ΨEP, 3 (rad)1020304050

Centrality(%)

centrality20-30%

−0.02
040

0050

1020

¨30

Centrality(%)

Systematic uncertainties

1
ϕ0.2

0.15

v3 EP, ∆η > 0.9 (unbiased)statistical uncertainties
Pb-Pb sNN = 2.76 TeV

systematicuncertainties
FMD A+C

1.4

20% large q2

statistical uncertainties
systematic uncertainties

1.4

1.2

1.2

11005

10155101520

ALI−PREL−116553

20252530353040354045504550

centrality(%)

centrality(%)

v3 EP, ∆η > 0.9 (ESE-selected)
v EP, ∆η > 0.9 (ESE-selected)
v3 3EP, ∆η > 0.9 (unbiased)

v2 EP, ∆η > 0.9 (unbiased)

v2 EP, ∆η > 0.9 (ESE-selected)> (unbiased)
0.9 (ESE-selected)
v2vEP,∆η ∆>η0.92 EP,

3ALICE Preliminary

30-40 %

final source

40-50 %

01ϕ23- ΨEP, 2 (rad)pairflow

Systematic uncertainties

0.1-2R 2long,n/ R 2long,02R 2side,n/ R 2side,00.20.30.20.10.3

ALICE Preliminary
0.20.100−0.1
0−0.1
0−0.1020400.3

0.1

0.20.100.2

204060−0.1
020

centrality (%)

2R 2os,n/ R 2side,00.1

0.3
0.22long,00.32long,n0.2

centrality (%)

00.1

−0.1
0−0.1
02R 2os,n/ R-22side,0R/R

0.3

60

4060

centrality (%)

0.3

2040

ALI−PREL−116570

centrality (%)

2040

centrality (%)

60

centrality (%)

ALICE Preliminary
0.20.3

Pb-Pb s NN=2.76 TeV

0.1π+π+ and π-π- pair combined

00.2−0.102040k T:0.2-1.5(GeV/c )60

centrality (%)

0.1q vector cut via FMD A+C side

π+π+ and π-π- pair combined¨

20% large q cut, n=22k T:0.2-1.5(GeV/c )

0.1

−0.1
0No q cut, n=2q vector cut via FMD A+C side

220% large q cut, n=22No q cut, n=26060

Pb-Pb s NN=2.76 TeV

02040

0.3

Relatives0amplitudes at−0.1
RHIC and LHC
40600are similar
incentrality centrality(%) (%)
magnitude andcentrality
dependence
20.2202040

220% large q cut, n=360

3No q cut, n=3204060centrality (%)

320% large q cut, n=33No q cut, n=33

✦ 20%Centrality(%)
largest q cut
1020304050

STAR Au-Au 200 GeV

0.15 < k T < 0.25 GeV/ c
0.25 < k T < 0.35 GeV/ clarger, while R 2side,2/R 2side,0 grows by ~10%

Relative
amplitudes for Rside
0.1
are proportional to the final
0.05
trangularityof the source
Initial triangular deformation is
30washed-outoreven
01020304050Centrality(%)
reversed
final
source✦20% largest q3 cut✓Although v is 20% enhanced with q vector cut, relative amplitude
does not change significantly
QM201702/08/2017

Conclusion✓Oscillation w.r.t. 3rd order event plane can be seen in Rout and Rside✓ ALICE has performed the first measurement of azimuthally

Toy Model shows similarsign of oscillations of Rsidefor kT>0.6 GeV

sensitive femtoscopy with q2 and q3 selection✓Large q2 selection enhances the oscillation of HBT radii✓A significant effect of large q3 selection on 3rd order oscillation of
HBT radii is not observed

flow anisotropy dominatedMgeometry dominatedCase (v =0)
Case (# =0)✦ Large
1.8 v2 and v3 events can be selected with 20% largest q2 and q3
ALICE Preliminary
1.8vector selection
ALICE Preliminary
FMD A+C

initial source

0.35< k T < 0.60 GeV/ c22
qn = (qn,x + qn,y )/20% large q2

20-30 %

initial source✓ v2 and v3 fluctuate event by event even in a same centrality✓ Q vector selection allows us to selectp event by event flow amplitude1.8 1.610-20 %

4050
Radii
relative amplitudes depend strongly on centrality andCentrality(%)
weakly on kT

Event shape engineering

1.6pair23- ΨEP, 2 (rad)Mohammad Saleh

Pb-Pb sNN = 2.76 TeV

0-5 %222222R/R,
R/R,
R/R
✓
out,2out,0out,2side,0os,2out,0 increase by ~20%
Results:
Azimuthal
HBT
w.r.tvplane
1430.2k T : 0.2-1.5 (GeV/c )00Centrality(%)

50

centrality0-5%

20-2R 2out,n/ R 2out,050

STAR Au-Au 200 GeV
0.04
Relative amplitude
0.15 < k T < 0.25(3rdGeV/ corder event plane)
0.25 < k T < 0.35 GeV/ c0.15

Pb-Pb sNN = 2.76 TeV+ +1010Large q2 event

k T:0.2-1.5(GeV/c )0-2R 2out,n/ R 2side,00

R 2os,2/ R 2side,0pair

1.5
2 −0.15
0- ΨEP, 3 (rad)R 2long,2/ R 2long,0ϕ

0.05

0R 2long,2/ R 2long,010.1−0.1

R 2os,2/ R 2side,00.5

pair

Systematic uncertainties

20% large qFMD A+C cut

0.3

0100R 2long (fm2)

−0.05

0.05

−0.1

10

ALICE Pb-Pb 2.76 TeV
0.2 < k T < 0.3 GeV/ c
0.3 < k T < 0.4 GeV/ c0.4 < k T < 0.5 GeV/ c
0.5 < k T < 0.7 GeV/ c023- ΨEP, 2 (rad)0.35
0.3-2R 2out,n/ R 2side,030

0.1

1
ϕ

0.4

100R 2side,2/ R 2side,0ALICE Pb-Pb 2.76 TeV
0.2 < k T < 0.3 GeV/ c
0.3 < k T < 0.4 GeV/ c
0.4 < k T < 0.5 GeV/ c
0.5 < k T < 0.7 GeV/ c00.45−0.10020(φpair-Ψ3=0)

R 2out,2/ R 2side,030in-plane2flow

40-50 %

23T2

final source

0.5

Azimuthal HBT w.r.t v2 plane
Relative amplitude 8(2nd Results:order event plane)40

R 2side,2/ R 2side,0R 2side (fm2)40

R 2out,2/ R 2side,0R 2out (fm2)

HBT radii w.r.t. 3rd order event planeT1

20-30 %
30-40 %ALICE Preliminary-2R 2out,n/ R 2out,0!
kT =initial source

Relative amplitude with ESE✓ 3rd order oscillation of HBT radii was observed in Rout and Rside✓ Same sign oscillation of Rout and Rside, while opposite sign in 2nd order
event plane dependence✓R 2side,3/R 2side,0 is negative without strong centrality dependence✓R 2side,2/R 2side,0 is positive with substantial centrality dependence✓R 2side,3/R 2side,0 in lowest kT is smaller than that in highest kT➡ Indication of kT dependence?
out-plane(φ -Ψ =π/3)
Rout22✓R side,2/R side,0 has clear kT dependence
Rside(p! + p!)10-20 %

✦ Opposite sign oscillation of Rout and Rside✓ Initial out-plane extended elliptic shape preserved at freeze out✦ Large q2 event cut enhances the Rout oscillation✦ Rside slightly changed with q2 cut

triangular flow(large)

pairpair

20

final source ??

triangular flow

0-5 %5-10 %

initial source
Ψ3230

02
3- ΨEP, 2 (rad)30

Large q3 cut

final source ?

No q cut

λR 2long (fm2)

02R 2side,n/ R 2side,0Ψ3

Pb-Pb sNN = 2.76TeV

10ALI-PREL-116566

initial source

40

20

10

Event shape engineering(ESE) is a technique proposed to select event by
event flow fluctuations[1].
Azimuthally differential HBT with large v2 and v3 event selection will give us
the new insights into the relation between anisotropic flow and thesource shape at freeze out and the dynamics of system evolution.
No q3 cut

No q2 cut

5-10 %✓P◆
1wi sin(n i )1
Ptann =nwi cos(n i )✦ Event planeR 2side (fm2)

Radii oscillation with ESE

3

1.8

Pb-Pb s= 2.76 TeVNNALICE Preliminary

1.6

Mohammad Saleh

QM201702/08/2017

FMD A+C

20% large q3

Pb-Pb sNN = 2.76
TeV
statisticaluncertainties

1.6

References

FMD A+C20% largeq3
systematicuncertainties

1.4

statistical uncertainties
systematic uncertainties

1.4[1] J. Schukraft, A. Timmins and S. A. Voloshin, Phys. Lett. B719, 394 (2013)

1.2

1.2

1
1005

ALI−PREL−116557

5101520101520252530303535
404540455050centrality(%)

centrality(%)

Naoto Tanaka s1430089@u.tsukuba.ac.jp