Back-to-Back Jet analysis with PYTHIA and
HYDJET++Hiroki Yokoyama
Univ. of TSUKUBA
2
Motivation J-Cal performance at Back-to-Back Jet
physics Which method is most excellent to find
Back-to-Back Jets in Heavy Ion Experiment? Resolution of primary-parton energy
Simulation with PYTHIA and HYDJET++
3
Jet Finding in pp CellJet algorithm track by track energy smearing
charged particles : ALICE TPC+ITS momentum resolution(assume pion mass)
neutral particles : ALICE EMCal energy resolution find jet using Visible(neutral+charged) or Charged
particles parameter
value
ConeRadius
0.2
eT-seed 20GeV(Visible), 13GeV(Charged)
Min-eT 1.5GeV(Visible), 1GeV(Charged)
4
Back-to-Back Jet Physics in pp
PYTHIA8 CellJet Jet-Finding algorithm R=0.2 (η-φ space) Dijet
coplanarity = |φJet1-φJet2| - π energy balance = parton energy resolution = ΔeT/eT
Coplanarity, energy balanceand energy resolution
are improved by installation of Calorimeter.
€
eT jet1 − eT jet 21 2 ⋅(eT jet1 + eT jet 2)
jet1jet2
5
Jet Finding in Pb+Pb
Generate samples of PYTHIA Dijets using PYTHIA8 CellJet algorithm(R=0.7) Embed these jets in Heavy-Ion events generated by HYDJET++ generator Find Back-to-Back Jets using CellJet corrected for Heavy-Ion experiment(CellJet’) calculate S/(S+B), efficiency, jet-energy resolution and parton-energy resolution
HYDJET++ event
S/(S+B)efficiency
energy resolution
PYTHIA8 Dijet event Jet
Finding
6
HYDJET++(HYDrodynamics plus
JETs) HYDJET++ is one of the event generators for
relativistic Heavy Ion Collision. The soft part : "thermal” hadronic state FASTMC The hard part : hard part of
HYDJET(PYTHIA6.4xx + PYQUEN1.5)
I choose the option “Hydro+ Jet (without quenching)”,and assume these events don’t have high energy Jets.
7
CellJet’(Jet Finding Algorithm)
1. divide η-φ space in [0.1, 0.1] cells2. calculate transverse energy (eTcell) in each cell3. BKG selection (BKG=〈 eTcell〉
(eTcell<“threshold”)×(1+v2*cos(dφ)) )4. subtract BKG from eTcell (eTcell = eTcell –
BKG(centrality,φ)) 5. select candidates of jet-seed by eTcell > ”eTseed”6. calculate sum of eTcell in the cone(with “Cone-
Radius”) which center positioned at jet-seed (eTsum=ΣeTcell)
7. requirement : eTsum>”Min-eT”8. define the survivors as found jets
input parameters in CellJet :“threshold”, “Cone-Radius”, “Min-eT” and “eT-seed”
threshold, coneRadius
8
Cone
-Rad
ius
Threshold[GeV]
100GeV Jet 0-
10%30-40%
60-75%
Single jet resolution = ΔeT/eT select “Cone-Radius” and “threshold” with better resolution
9
S/(S+B)efficiencyS/
(S+B)*effciency
Min-eT, eTseed• S/(S+B) ≡ Nreal/Nfound
• efficiency ≡ Nreal/Nembed
Nreal : # of found Back-to-Back Jets from PYTHIA DijetNfound : # of found Back-to-Back Jets by CellJet’Nembed : # of embedded DiJet (1)
definition of Back-to-Back Jet|dφ-π|<0.3
Comparison with PYTHIA-Jetsdistance btw embedded jet and
found jet < 0.15|eTpythia jet-eTfound jet|/eTpythia jet <
0.45
Select “Min-eT” and “eTseed” with better S/(S+B)*efficiency
In other centrality and other energy,the same trend is seen.
0-10%50-100GeV
10
parameter settingparameter valuethreshold 15GeVConeRadius centrality functioneT-seed 50GeV*0.15 = 7.5GeVMin-eT 50GeV*0.5 = 25GeV
50GeV Jet configurationeT-seed & Min-eT should be
constant
11
Energy ResolutionSingle Jet Energy
Resolution
compare found Jet eT with embeded Jet eT
Parton Energy Resolution
compare found Jet eT with primary parton eT
25%(central) 12%(peripheral)
30%(central)17%(peripheral)
12
DiJet: S/(S+B), efficiency
mid-central~peripheral Good S/(S+B) and efficiency
central ~40% noise
13
Summary / Plan J-Cal performance at Back-to-Back Jet physics
For Back-to-Back Jet physics, Calorimeter opposite side of ALICE EMCal(J-Cal) will give good performance.
How to find Back-to-Back Jets in Heavy Ion Experiment try “CellJet’” algorithm search other better method
primary-parton energy estimation energy resolution ~30%(central) with Jet-Quenching?
14
backup slide
coplanarityR=0.2 R=1.0
energy balanceR=0.2 R=1.0
parton energy resolution
R=0.2 R=1.0
18
quark jet fraction fraction of quark/gluon which is created from most
hard pp collisions (sqrt(s)=5.5TeV) as a function of pTHat
19
Energy Resolution correlation btw PYTHIA eTJet & PYTHIA+HYDJET inclusive eTJet
calculate the correction factor resolution = RMS of “(eTPYTHIA_Jet – eT’corrected)/(eTPYTHIA_Jet)” select “Cone-Radius” and “threshold” with better resolution
threshold, coneRadius
20
50GeV
100GeV
150GeV
0-10%
20-30%
40-50% 60-75%
Cone
-Rad
ius
Threshold[GeV]
21
Min-eT, eTseed50~100G
eV
100~150GeV
150~200GeV
0-10%
20-30%
40-50% 60-75%
Min-eT/pTHat
eTse
ed/M
in-e
T
22
ConeRadius Estimation in PbPb
with Charged Particles pT>2GeV particles PYTHIA + HYJING
23
Jet Energy Resolution
in pp Using charged Particles Jet (not Parton) Energy resolution Jet energy : sum of energy All Final particles in R=1.