HBT measurement with respect to event plane and jet axis
in Pb-Pb 2.76 TeV collisions from ALICE
Naoto Tanaka for the ALICE Collaboration

order event plane(Ψ2) offers the detailed analysis

Impact of re-distributed energy on bulk size ??
➡ Explore via HBT !

21ch2
2
R out (fm )The results shows explicit oscillation andopposite sign of Rout and Rside.

40
30

2
2
R side (fm )w.r.t. Ψ2 into several bins) .

2
R long (fm2)at freeze out (Dividing pair emission angle

2
2
R out (fm )HBT w.r.t. Ψ2 can measure the source shape50504050

1π/2< 5 GeV/ c , |ηtrack30

ρ (ϕ )

ρ (1+2v cos(2[ϕ-Ψρρ (1+2v cos(3[ϕ-Ψch0002013]))EP, 223]))

EP, 32045102

ϕ33π/4Pairπ00- ΨEP,2 (rad)Pb-Pb sNN = 2.76 TeV

6ϕ (rad)π/4

1π/22ϕPair

3π-Ψ

0.7
0.3 < k T < 0.4 GeV/ c0-5% centrality

400.6

5-10% centrality
10-20% centrality

303040| < 0.9λAzimuthally sensitive HBTπ/4T, track

Pb-Pb sNN = 2.76 TeV

out-of-cone

100100050

Out-of-Cone
ΔR<0.8✦ Event planes(Ψ2, Ψ3) are determined with VZERO detector

0150
Quark Matter 2011, Annecy

20ALICESingle event

50 0.15 < p303 ])}Pb-Pb sNN = 2.76 TeV

arXiv:1102.1957 [nucl-ex]• Exclude leading jet area (R < 0.3)
• 2nd + 3rd order Fourier decomposition of
azimuthal distribution of emitted
50 particles
in a given event• Subtract the jet background including
40v2 and v3 modulation

200In-Cone
ΔR<0.8ρ (ϕ) (GeV/c )✓Event by event background subtraction

obsobs: ⇢(') = ⇢0 ⇥ 1 + 2{v2 cos(2 ['2 ]) + v3 cos(3 ['✓ Background density
subjetjetjet✓ Jet pT after subtraction : pjet=pArea⇥⇢(')
TT

Christof Roland (talk at QM2011)✦ Geometrical modification

Jet reconstruction• Resolution parameter : R = 0.2• Jet background is calculated with E-by-E estimation• pTjet > 20 GeV/c after bkg. subtraction• leading hadron pT > 5 GeV/c⬛ pT : 4 - 8 GeV/c⬛ pT : 1 - 4 GeV/cof freeze-out source shape.
In this poster, a new method to measure the jet
modification effect with HBT is presented✓Analysis uses Run1 Pb-Pb collisions in 2011
✓Charged jets are reconstructed with TPC+ITS⬛ pT : 8 GeV/c -2
2
R side (fm )What are the characteristics of the jet
modiﬁcation in the geometrical space ?

Sub leading jet

HBT correlations using quantum interferometryof identical particles provide a unique tool
to measure the source size at kinetic freeze-out.
In particular, azimuthally sensitive HBT w.r.t. 2ndChristof Roland

The jet energy deposition in the medium
was found to result in an increased productionof low pT particles at large angles opposite tothe survived jet or trigger γ direction[1][2] .

Leading Jet

Introduction

20-30% centrality

0.530-40% centrality
40-50% centrality

Furthermore, comparing the initial and ﬁnal
source shape, system evolution can be investigated.

20200.4

10

10

100.3

00ϕ

33π/4

Pair

100ππ/4 0π/2 π/4ϕ- ΨEP,2(rad)ALI−PREL−60322

2 1Pair

3π/4 π/2

3π23π/4- ΨEP,2 (rad)ϕ -ΨPair340

π 0EP,2 (rad)! 1 !
kT = (pT 1 + pT!1 )π/42
π/2
1ϕ2Pair

0.3 < k T < 0.4 GeV/ c

05-10% centrality
10-20% centrality
20-30% centrality

0.530-40% centrality

ALICE

ch jetv20-5%, Stat unc.

0.2

π/4

HBT w.r.t. Jet axis
- Jet medium interaction- re-distribution of low pT particles- Jet background subtraction method

Pb-Pb sNN = 2.76 TeV

Syst unc. (shape)

π/2

0.1
ALI−PREL−60322

ϕPair

33π/4

HBT w.r.t. Ψ2‣initial geometry‣collective ﬂow‣( event plane resolution )R = 0.2 anti-k T, |η |<0.7

Syst unc. (correlated)
2Jet - Ψ2 correlation

0.4

Syst (correlated)

140-50% centrality

jet

0.3
0π

10- ΨEP,2 (rad)

π/4

2π/2

ϕ

3

3π/4π

- dependenceΨEP,2 (rad)ΨPair 2φJet

In order to understand jet modiﬁcation in source shape,

④030

①③(a)

✴HBT w.r.t. jet axis ①-④, ②-③ should be symmetric
about jet axis

00.70.6

is observed[3]. Therefore HBT w.r.t. jet

Selecting jet axis w.r.t. Ψ2 (Ψ3) is important.

✓Pair transverse momentum

0-5% centrality

0axis will also include Ψ2 HBT signal.

π/2250If jet modiﬁcation aﬀects medium shape, azimuthally sensitive30
HBT should have the oscillation with respect to the leading
jet axis.
In HBT analysis, momentum range is very low(pT:0.15-2.0 20
GeV/c).
So this analysis will be sensitive not to size of jet itself
10
but to the bulk response and re-distributed hadrons.
Recently non zero jet v2

π/4

10λ2R long (fm2)

Analysis method

20ch jetv 2 {EP, |∆η|>0.9 }This indicates the source keeps the initialelliptic shape until freeze-out.

p40

Summary✓ HBT w.r.t. jet axis is a new method to investigate the jet modification✓ Momentum range is preferable to measure the bulk response✓ Finite jet v2 causes other contributing factors to HBT w.r.t. jet axis
➡ Selection of jet axis w.r.t. Ψ2 is important

50

60

T, track> 0.15 GeV/c , p70

OutlookT, lead> 3 GeV/ c②8090100ch jetp(GeV/c )! !!

! !

②③① ④TΨ2① out-plane jet1
② in-plane jet1
③ in-plane jet2
④ out-plane jet2

✓Azimuthally sensitive HBT w.r.t. jet axis
• kT dependence• Resolution parameter dependence
References[1] S. Chatrchyan et al. (CMS Collaboration) Phys.Rev.C 84, 024906(2011)[2] A. Adare et al. (PHENIX Collaboration) Phys. Rev. Lett. 111, 032301[3] arXiv : 1509.07334 [nucl-ex]

Naoto Tanaka
s1430089@u.tsukuba.ac.jp

IMAGINE THE FUTURE ..

3π-Ψ