1LHC-ALICE 実験におけるジェット測定のジェット抑制効果による影響

17/10/2009
Dousatsu Sakata for the ALICE Collaboration
University of Tsukuba & RIKEN
JPS 2010 spring

2010/03/20

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OutlineJet Physics for Nuclear Collisions
Motivation
ALICEEvent Generator [QPYTHIA&QPYTHIA]
Jet Finding Algorithm [FASTJET]Analysis Flow
Result
Jet Finding Performance
RAA of Di-Jet

Summary & Outlook

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Jet Physics for Nuclear Collisions

JPS 2010 spring

2010/03/20

Jet is very useful probe forinvestigating the hot & dense
matter created by ultra
relativistic heavy ion collisions.

 Mach Cone
 E loss in QGP (jet quenching)- Collisional energy loss
- Radiative energy loss

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4Motivation

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To know the effect of Jet quenching ,varied studies of particle levelhas been measured at RHIC.

RHIC“Particle level study”

LHC-ALICE“Jet level study”

In order to do accurate jet level measurement for "Jet Quenching”,
it is necessary to evaluate the quenching effect on Jet-Finding.

5A Large Ion Collider Experiment

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ALICE is optimized to study heavy ion collisions.
Pb+Pb collisions will be studied at √s = 5.5TeV

Central detectors
ITS,TPC,TRD,TOF,EMCAL,PHOS,HMPID
Forward detectors
FMD,V0,T0,ZDC,PMD,Muon
First paper was accepted
at 28 Nov. 2009!
arXiv:0911.5430

6PYTHIA & QPYTHIAJPS 2010 spring

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PYTHIA : event generator for pp collisions
http://home.thep.lu.se/~torbjorn/Pythia.html
QPYTHIA: event generator including quenching effect [arXiv:0906.0754]
based on BDMPS model[Phys. Rev. C58 (1998) 1706]
Radiative energy loss : gluon radiation
Collsional energy loss : energy flow from parton to matter
Increase low pT
hadrons

Decrease high pThadrons

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FastJetFastJet: sequential clustering algorithms

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http://www.lpthe.jussieu.fr/˜salam/fastjet/ p = 1 k algorithm
2T
2p
2 p ΔRdij = min(k ti ,k tj ) 2  p = 0 Cambridge/Aachen algorithm
R  p = −1 anti-kT algorithm€Procedure of Jet Finding
Calculate particle distance : dij
Calculate Beam distance : diB=kti2p
Find smallest distance (dij or diB)
If dij is smallest combine particles
If diB is smallest
and the cluster momentum
larger than thresholdcall the cluster a Jet.

Parameters- R size (= √dϕ2 +dη2)- pT cut of single particle- Jet momentum threshold

arXiv:0802.1189v2[hep-ph] (2008)

KT jet Cone jet8Analysis Flow

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PYTHIA event

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QPYTHIA event√s = 5500GeV√s = 5500GeV
centrality : 0-10%
qhat: 20 GeV2/fm

All stable particles are adapted to Jet Finding.
Detector smearing is not included.
No thermal background particles.

FASTJET [anti-kt , kt , cambridge]

Jet Selection for the analysis
2-parton in |eta|<1
2-Jetin |eta|<1
Back-to Back Jet [cos(φJet1 - φJet2)<-1/√2]
Axis resolution
Energy reconstruction
Yield

JF Performance
RAA

Axis resolution
Energy reconstruction
Yield

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Jet Finding Performance

JPS 2010 springthreshold : 20 [GeV/c]

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PYTHIA QPYTHIA

dφ =φparton - φJet
dET=dETparton - dETJet

anti-kT algorithmkT algorithm

Axis resolution

Energy reconstruction

Axis resolution is about
40% broad due to quenchingdEt is shifted about 20GeVby quenching effect10

RAA of Di-Jet

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threshold : 20 [GeV/c]

Di-Jet yield of quenched Jet is
15% of the yield of unquenched Jet at R=0.4
RAA is getting larger with increasing R.

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Summary & Outlook
Tested several Jet Finding algorithms
w/wo quenching effect.
▫ Axis resolution is about 40% broad due to quenching effect.
▫ dET is shifted about 20GeV by quenching effect.
▫ RAA of Di-Jet is about 0.15 at R=0.4

Evaluate Jet Finding performance with background.
Evaluate possibility of reconstruction of Energy loss.

Thank you very much

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JPS 2010 spring

Backup2010/03/20

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Event Generation & Selection
PYTHIAp+p 5500GeVQPYTHIAPb+Pb 5500GeV
Centrality : 0-10%
qhat: 20 GeV2/fm

All stable particles are adapted to Jet Finding.
Detector smearing is not included.
No background particles.

JPS 2010 spring

Status of PYTHIA & QPYTHIA(tuned for ALICE)
AliRoot

v4-17-01# of event

10000

ProcessAll QCDon

ϕ0 ~ 2πη-1 ~ 1Jet Selection for the analysis
2-parton in |eta|<1
2-Jetin |eta|<1
Back-to Back Jet [cos(φJet1 - φJet2)<-1/√2]
To evaluate “Quenching effect” with Jet Finding,
it is necessary to minimize
the other higher order effects.

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