Systematic study of elliptic andhigher order harmonics by event
plane method in Pb-Pb 2.76 TeV
collisions at LHC-ALICE
Workshop on Particle Correlations and Femtoscopy
September 24th, 2011	

Masato Sano for the ALICE collaboration
University of Tsukuba

1JSPS	

Outline	n Introduction
What’s collective flown Motivationnn ALICE detectorn vn measurement by Event Plane methodn Event Plane resolutionn Results
Centrality of v2 ,v3 ,v4n pT dependence of v2 ,v3 ,v4n

2n Summary

What’s collective flow	
Initial spatial anisotropy
Ψ2	eccentricity(n=2)
triangularity(n=3)
quadrangularity(n=4)...

pressure gradient	
Momentum space anisotropyn n-th fourier coefficient of dN/d(φtrack-Ψn) dist.

vn = �cos(n(φ − Ψn ))�
n Sensitive probe for early stage of heavy
ion collisions.

3Ψ3	Phys.Rev.C82:034913,2010	

Motivation	n How does collective flow manifest itself at LHC?
Constraints on η/s and initial condition (CGC/Glauber).
n Does quark number and KET scaling work atLHC ?
n Are ridge and mach cone like structure fully
explained by higher order flow ?
n

PRL104 (2010) 062301
Phys.Rev.Lett.104.062301	

Phys.Rev.Lett.98:162301,2007	

ridge	
4

Mach cone like structure	ALICE detector	
n TPC & ITS
Charged particle
trackingn VZEROn

Scintillation counter.
n Event triggern Centrality
determinationn E.P. determinationn FMDn

Silicon strip detector.
n E.P. determination

5nALICE detector 	

VZERO	n In this analysis, vn at mid-rapidity ismeasured using Event Planes atforward rapidity.
This introduce large rapidity gap toreduce non-flow bias on vnmeasurement.
n TPC & ITSn

0<Φ<2πn |ηtrack|<0.8n VZEROn

FMD	0<Φ<2π : Divided into 8 segmentsn V0A: 2.8 < η < 5.1n V0C: -3.7 < η <-1.7n 0.9<|ηtrack-ηVZERO|<5.9n FMDn

0<Φ<2π : Divided into 20 segmentsn FMDA : 1.7 < η < 5.0n FMDC : -3.4 < η <-1.7n 0.9<|ηtrack-ηFMD|<5.8n

6Event plane	vn measurement by E.P. method	① Determine E.P. in sub event i : Ψni② Measure vnmeas.{ EPi }vnmeas.{ EPi } = <cos(n(φtrack-Ψni))>③ Extract Res{Ψni } from E.P. correlations④ Correct vnmeas.{ EPi } by E.P. resolution7

vn { EPi } = vnmeas.{ EPi } /Res{Ψni}E.P. resolutions for n-th order plane	n E.P. resolutions are extracted by 3 sub event method.

n These excellent resolutions allow us to measure v2, v3 and v4 .

8

��
�
�
�
�
� �cos n(Ψin − Ψjn ) ��cos n(Ψin − Ψkn ) ����cos n(Ψin − ΨTn rue ) � = ����cos n(Ψjn − Ψkn ) �centrality dependence of vn 	
0.2<pT<5.0GeV/c	n v3 and v4 have a weak centrality dependence compared to v2 .

9n Results on vn{EP} (this analysis) and vn{2,|Δη|>1} (PRL, obtained from 2-part.corr. using
TPC tracks) are fully consistent.

pT dependence of vn 	n Results on vn{EP}(this analysis) and vn{2,|Δη|<1}(PRL, obtained from 2part.corr. using TPC tracks) are fully consistent.
nnecessity to consider higher order flow for the study of di-hadroncorrelation especially for central collisions.

10n v3(v4) is as large as v2 at about 1.6 GeV/c (3.0 GeV/c) for 0-5% central

Summary & Outlook	n vn (n=2,3,4) are measured using E.P. determined by forward detectors in
Pb-Pb collisions at sqrt(sNN)=2.76 TeV with ALICE detector.
nResults on vn{E.P.} and vn{2, |Δη|>1}) are fully consistent.

nCentrality dependence of v2, v3 and v4 .
n

pT dependence of v2, v3 and v4 .
nn

v3(v4) is as large as v2 at about 1.6 GeV/c (3.0 GeV/c) for 0-5% central
Comparison with hydro. predictions (Glauber initial condition)
η/s=0.08 favored with respect to ideal hydro.
n

11n

v3 and v4 have a weak centrality dependence compared to v2