Event Plane dependent dihadron azimuthal correlations with event
shape engineering in Au+Au collisions at 𝒔𝑵𝑵 =200GeV
Ryo Aoyama, for the STAR Collaboration
University of Tsukuba, CiRfSE
Abstract
Dihadron azimuthal correlations with high pT trigger particles are a valuable tool to study the interactions between jets and the QGP medium. Previously, it was shown that
dihadron azimuthal correlations are expected to depend on the azimuthal angle of trigger particle relative to the event plane[1]. However, in-medium path length can
additionally differ in the same multiplicity class because of the evolution of the system, and thus the strength of long-range correlations (flow), is sensitive to fluctuations in
the initial geometry. Event shape engineering (ESE) has been proposed as a powerful method to select the events which have different strength of flow[2].
We present a study of dihadron correlations for different selections of trigger particle’s azimuthal direction with respect to the event plane in Au+Au collisions at 𝑠JJ =200GeV utilizing ESE.

Motivation
Ø Why distinguish “Left” and “Right”?
Event Plane(EP) dependence of correlations has been measured in Au+Au
collisions[1], but in this measurement Left / Right difference with respect toΨC leads to a different in-medium path length.

Analysis methodØ Why event shape engineering (ESE)?
The amplitude of flow is sensitive to the initial geometry of the system. By
selecting the size of the flow vector (|Q2|), we can choose different strengthof flow. The difference of jet modification in strong flow events and in weakflow events could be measured.

ü Correlation Function
Rd( )d( ⌘)Y mix (C( , ⌘) = R
d( )d( ⌘)Y real (Statistical errors are smaller than marker size.

ü Event classification

Ø Q2 cut with TPC EP in each centrality class
𝑄C =C

𝑄CO + 𝑄CQ= asso
⌘ = ⌘ asso

𝑄CO = ∑ 𝑤0 cos(𝑛𝜙0 )𝑄CQ = ∑ 𝑤0 sin(𝑛𝜙0 )C, ⌘) Y real (· mix(, ⌘) Y, ⌘), ⌘)trig⌘ trigØ In order to remove the effect of acceptance and efficiency of detectors from signals ,distributions of real event is divided by mixed event.
0-5%STAR preliminary

1Nevents

STAR preliminary0.5−1

Event Plane dependence
Trigger

1.05

Ø Both Q2 and EP(ΨC ) are measured in η<-0.5 (η>0.5)
Ø Correlations are measured on the opposite side ofTPC, at η>0 (η<0).
Q2 cutEP-10< 𝜙) <@1
0.5−0.5−0.5

Δ𝜂 −1 −1

1.1

0.9

−0.5

0.8

0123

1230.5−0.5
0123−1𝜋< 𝜙) < 08123

0.9−0.5

4 −1 −1

1.1

0.9

4 −1 −1−0.5

Δ𝜙0123−3𝜋−2𝜋< 𝜙) <881.3

1.450-60%0< |𝜙) | <1.41𝜋2𝜋< |𝜙) | <881.3>?

@ 1.3STAR preliminary

0.90.90.80.8

1.42𝜋3𝜋< |𝜙) | <881.3

1.2

1.1

1.1

1.1

1111

0.9

0.9

0.9

0.9

1.2

1.2

C2 1.1−1012

34−101234−1Δ𝜙012

3−1012

34

1.2

1.2

1.1

1.1

1

0.9

0.9

0.8

0.8

012
3−4𝜋−3𝜋< 𝜙) <8844w/o Q2 cut

3𝜋4𝜋< |𝜙) | <88φs>0φs<0−101234Ø In Δφ, Δη correlations, long-range azimuthal correlation can be seen regardless ofthe trigger particle’s angle (φs).
Ø Mirror symmetric distributions with respect to Δφ=0 can be seen in each panel.

−4𝜋−3𝜋< 𝜙) <8820-30%

1.4
1.2
10.95

0.8
1.4

012

34−10

1 −3𝜋 23 −2𝜋 4

0.8
1.4

88

1.2

1.2< 𝜙) <

11

1

0.95

0.8
1.4

0.8
1.4

012

34−101.2123−2𝜋−1𝜋< 𝜙) <88401231

1

0.95

0.8
1.40.81.401234−101.2123−1𝜋< 𝜙) < 0844Δφ110.95

0.8
1.4

0.8
1.401234

1.05−101.212>?
0< 𝜙) <@

34

110.95

0.8
1.4

0.8
1.4

01234−101.22
1𝜋 12𝜋< 𝜙) <8834

110.95

0.8
1.4

0.8
1.4

1234

1.05

−1012𝜋3𝜋 2< 𝜙) <
88

1.2

34

110.95

0.8

0.8

01234

1.05

1.4

−1 3𝜋 0

14𝜋

1.288

< 𝜙) <2341.4

110.950.80.801234−10134w/o Q2 cut−10123420% high Q2 cut−10123420% low Q 2 cut−1012< 𝑝-2./01−101 < 𝑝- ;))< < 2 (GeV/c)

1−10−103423412341234< 4 (GeV/c)

1.2

1−122

Δ𝜙

out-of-plane

in-plane

1.2

1−11|Δη|<0.5

1.2

1001.21−1−1STAR preliminary

1.2

1−150-60%

1.2

1−14 −1 −12<pTtrig<4(GeV/c)
1.2
1<pTasso<2(GeV/c)|Δη|<0.5

1.2

1Projection to Δφ axis
1.44 Δφ

1.4

1.05010.80123−2𝜋−1𝜋< 𝜙) <
88

1.1

0.501

0.8−1 −10

1.101

1.2

4 −1 −10.5
1.1−0.5−0.5

1.2

0.5

0

0.9

4 −1 −1

1.2

1.201

0.80C23𝜋4𝜋< 𝜙) <880.501

4 −1 −1

η1

0.501

3

1.05

1.2

1.101

10.52

1.05

2𝜋3𝜋< 𝜙) <88

1.2

11−12<pTtrig<4(GeV/c)
50-60%
w/o Q2 cut 1<pTasso<2(GeV/c)

101.0501𝜋2𝜋< 𝜙) <88>?

−10.8

1−1Correlations as a function of 𝜙)STAR preliminary-0.5Projection toΔφ axis

0-5%

−1

Two particle
correlation

𝜂 gap

1

ü Q2 dependence of correlation function

ü Event Plane dependent correlation function

𝜙𝑠 = 𝜙𝑡𝑟𝑖𝑔 − Ψ2|∆η|<0.5
0.5|∆η|<10.5<|Δη|<1

1.2

−0.5

High Q2

2<pTtrig<4(GeV/c)2<pTasso<4(GeV/c)

1.4Δη 0Low Q2STAR preliminary

50-60%34out-of-plane−101234

Ø Peak positions shift as a function of φs.
Ø Q2 dependence can be seen in each centrality class.

Summary & Outlook
Ø Peak positions of correlations shift as a function of φs.
Ø Long-range correlation can be seen regardless of φs.
Ø Q2 dependence can be seen in raw correlation functions.
Ø Background subtractions will be done.
Ø Correction of event plane resolution will be done.
Ø Systematic uncertainties will be calculated.

References[1] Adamczyk L et al. (STAR) 2014 Phys. Rev. C89 41901[2] Jurgen Schukraft, et al. 2013 Phys.Lett. B719 394-398

IMAGINE THE FUTURE.
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