JET AND DI-JET RECONSTRUCTIONUSING HYDJET++
Hiroki Yokoyama
Univ. of Tsukuba

Celljet (the Jet-Finding Method)
2.

calculate transverse energy (eTcell) in each cell

3.

subtract mean BKG defined by HYDJET HD event from eTcell(eTcell = eTcell – BKG( centrality,φ,η))4.

select candidates of jet-seed by eTcell > ”eTseed”

5.

calculate sum of eTcell in the cone which center positioned at jetseed (eTsum=ΣeTcell)

6.

requirement1 : eTsum>”Min-eT”

7.

requirement2 : eTseed/eTsum>”frac”(eT fraction of jet-seed)8.

define the survivors as found jets

Parameters to input are“eTseed”, “coneRadius”, “Min-eT” and “frac”

Phtoton and Jet in ALICE

divide -1<η<1 ,-π<φ<π region in [0.1, 0.1] cells
08.12.4

1.

2

Parameter Selection (“coneRadius”)
08.12.4

 PYTHIA simulation (pp 5500GeV quark-jet) distance btw Celljet center and each track (eT weighted)

Phtoton and Jet in ALICE

calculatedistance

3“coneRadius” = 0.25 is sufficientParameter Selection (“frac”)
distance btw Celljet center and each track (eT weighted)->ProjectionY eT fraction against jet-eT(R=0.4) as a function of length from Celljet center

08.12.4

Phtoton and Jet in ALICE

region ofjet-seedjet eT range: 20-100GeV

4

seed-eT fraction “frac” = 0.3 is selectedAnalysis Flow

2.

4.
5.
6.

PYTHIA single/
back-to-back jet
data set
HYDJET++
HD+jet event

Celljet analysis

Phtoton and Jet in ALICE

3.

prepare data of single/back-to back jet by PYTHIA 5500GeV pp
collision at each jet-eT region
prepare data of HD+Jet event using HYDJET++ √s=5500GeV
PbPb collisionembed a PYTHIA jet into a HD+Jet event
analyze using Celljet method, then find single/back-to back jetscompare the direction of embedded jet with those of found jets
calculate S/N

08.12.4

1.

R<0.15check the answer&calculate S/N5

Quality of Single-jet Finding HYDJET “HD+Jet” event + PYTHIA single-jet
08.12.4

 charged pion, proton and photon tracks are used
 “Min-eT” = 20[GeV], “eTseed” = “Min-eT”*0.3 is selectedcentrality→peripheral

S/N (0~1.2)

central ←Phtoton and Jet in ALICE S/N≡ (# of found PYTHIA jets)/(# of found jets)at peripheral and at high jet-eT
S/N become close to 1
pythia jet eT[GeV] (20GeV~140GeV)

6

CELLJET – BACK-TO-BACK JET FINDING

Phtoton and Jet in ALICE |Δφ|>17/18 * π [rad]08.12.4

 difference btw φ directions of found jets (Δφ)

jet1

jet2

when this angle is less than π/18,
7
they are recognized as “back-toback jet”.

Quality of Di-jet Finding
HYDJET “HD+Jet” events + PYTHIA di-jet(back-to back)charged pion, proton and photon tracks are used“Min-eT”=20[GeV], “eTseed”=“Min-eT”*0.3 is selected

S/N≡(# of found PYTHIA back-to back jets)/(# of found back-to back jets)→peripheral

S/N (0~1.2)

centrality

Phtoton and Jet in ALICE

central ←08.12.4



S/N(di-jet) is larger than
S/N(single jet)pythia jet eT[GeV] (20GeV~140GeV)

8

For J-Cal Projectback-to back jet finding quality using visible particle
( in case using EMCal and TPC → catch proton, pion and photon)
08.12.4

Detector
resolution is notincluded

back-to back jet finding quality using only charged particle( in case using only TPC → catch proton and charged pion )jet finding parameter : eT-Mincharged = eT-Minvisible * 2/3 (assume pion is dominant)centrality→peripheral

S/N (0~1.2)

central ←Phtoton and Jet in ALICE

Using visible particle is reasonable
to find back-to back jetin particular, central~mid-central regeon
pythia jet eT[GeV] (20GeV~140GeV)

9

Summarymethod

Phtoton and Jet in ALICE

parameter setting : “coneRadius”=0.25, “frac”=0.3
 jet finding (jet-eT = 20GeV) in PbPb √s=5.5TeV “HD+Jet”+PYTHIA jet jets of low-eT in central are difficult to be identified.
→ parameter tuning is necessary.
08.12.4

 Estimate the quality of jet finding using “Celljet”

 J-Cal

EMCal is very useful to find back-to-back jets in central ~mid-central collisions.
 → calorimeter at opposite side of EMCal is necessary in
ALICE environment.
10

08.12.4

Phtoton and Jet in ALICE11BACK UPPARAMETER SELECTION(CONERADIUS)

Phtoton and Jet in ALICEpythia.readString("HardQCD:gg2gg = off");
 pythia.readString("HardQCD:qqbar2gg = off");
 pythia.readString("HardQCD:qg2qg = off");
 pythia.readString("HardQCD:gg2qqbar = on" ); pythia.readString("HardQCD:qq2qq = on" ); pythia.readString("HardQCD:qqbar2qqbarNew = on" ); pythia.readString("HardQCD:gg2ccbar = on" ); pythia.readString("HardQCD:gg2bbbar = on" ); pythia.readString("HardQCD:qqbar2bbbar = on" ); pythia.readString("HardQCD:qqbar2ccbar = on" ); quark jet is selected for make jets have sharp shape CellJet cellJet(1., 20, 64, 2, 0, 0.5, 2, 0); cellJet.analyze( pythia.event , 0.8*pTHatMin, 0.4, 0.15*pTHatMin);08.12.4

 pythia celljet settings

13

PARAMETER SELECTION(FRAC)
distance btw celljet center and each track (eT weighted) ->ProjectionY

08.12.4



Phtoton and Jet in ALICE

14

frac = 0.3 is selected from integral

PARAMETER SELECTION(FRAC)
circle(R=0.25)

space of [0.1,0.1] square equal with that of circle(R=0.056)
0-50GeV50-100GeV

100-200GeV

200-400GeVratio

0.45

0.54

0.62

0.71

Phtoton and Jet in ALICEjet eT08.12.4

 integral in circle(R=0.056) / integral inparameter “frac” must be less than all ratio
then I selected “frac = 0.3”

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PYTHIA JET GENERATION SETTING FOR JET
ENBEDDING TO HYDJET











Phtoton and Jet in ALICEpythia.readString("HardQCD:gg2gg = off");
pythia.readString("HardQCD:qqbar2gg = off");
pythia.readString("HardQCD:qg2qg = off");pythia.readString("HardQCD:gg2qqbar = on" );pythia.readString("HardQCD:qq2qq = on" );pythia.readString("HardQCD:qqbar2qqbarNew = on" );pythia.readString("HardQCD:gg2ccbar = on" );pythia.readString("HardQCD:gg2bbbar = on" );pythia.readString("HardQCD:qqbar2bbbar = on" );pythia.readString("HardQCD:qqbar2ccbar = on" );quark jet is selected for make jets have sharp shape

08.12.4

 pythia celljet settings

CellJet cellJet(1., 20, 64, 2, 0, 0.5, 2, 0); cellJet.analyze( pythia.event , 0.8*pTHatMin, 0.25, 0.2*pTHatMin);
16

BKG HD EVENT DISTRIBUTION“Bgen” that mean the impact parameter<-phi-><-eta->

centrality→ central

Phtoton and Jet in ALICE

peripheral ←08.12.4

 centrality is defined by HYDJET parameter

17

CELLJET – BACK-TO-BACK JET FINDING

Phtoton and Jet in ALICE |Δφ|>17/18 * π [rad]08.12.4

 difference btw φ directions of found jets (Δφ)

jet1

jet2

18

when this angle is less than π/18,
define them “Di-jet”.

CHECKING ANSWER

 back-to-back jet

center of PYTHIA back-to-back jets :(φPYTHIAjet1,ηPYTHIAjet1),(φPYTHIAjet2,ηPYTHIAjet2)
 center of found jets : (φi,ηi) R1 = √(φ1-φPYTHIAjet1)2+(η1-ηPYTHIAjet1)2<0.15 and R2 = √(φ2-φPYTHIAjet2)2+(η2-ηPYTHIAjet2)2<0.15Phtoton and Jet in ALICE

center of PYTHIA jet : (φPYTHIAjet,ηPYTHIAjet) center of found jet : (φ,η)
 R = √(φ-φPYTHIAjet)2+(η-ηPYTHIAjet)2<0.15

08.12.4

 single jet

19

S/N : HYDJET-”HD+JET” + PYTHIA “SINGLE
JET”
08.12.4
Phtoton and Jet in ALICE

20

S/N : HYDJET-”HD” + PYTHIA “DI-JET”
08.12.4
Phtoton and Jet in ALICE

21

S/N : HYDJET-”HD+JET” + PYTHIA “DI-JET”
08.12.4
Phtoton and Jet in ALICE

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