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Back-to-Back Jet analysis with PYTHIA and HYDJET++

Back-to-Back Jet analysis with PYTHIA and HYDJET++. Hiroki Yokoyama Univ. of TSUKUBA . 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 .

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Back-to-Back Jet analysis with PYTHIA and HYDJET++

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  1. 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-partonenergy Simulation with PYTHIA and HYDJET++

  3. Jet Finding in pp • CellJet algorithm • track by track energy smearing • charged particles : ALICE TPC+ITS momentum resolution(assumepion mass) • neutral particles : ALICE EMCal energy resolution • find jet using Visible(neutral+charged) or Charged particles

  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 = • partonenergy resolution = ΔeT/eT jet1 Coplanarity, energy balance and energy resolution are improved by installation of Calorimeter. jet2

  5. Jet Finding in Pb+Pb • Generate samples of PYTHIA Dijets using PYTHIA8 CellJetalgorithm(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 PYTHIA8 Dijet event S/(S+B) efficiency energy resolution Jet Finding HYDJET++ event

  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) • divide η-φ space in [0.1, 0.1] cells • calculate transverse energy (eTcell) in each cell • BKG selection (BKG=〈eTcell〉(eTcell<“threshold”)×(1+v2*cos(dφ)) ) • subtract BKG from eTcell (eTcell = eTcell – BKG(centrality,φ)) • select candidates of jet-seed by eTcell > ”eTseed” • calculate sum of eTcell in the cone(with “Cone-Radius”) which center positioned at jet-seed (eTsum=ΣeTcell) • requirement : eTsum>”Min-eT” • define the survivors as found jets input parameters in CellJet : “threshold”, “Cone-Radius”, “Min-eT” and “eT-seed”

  8. threshold, coneRadius • Single jet resolution = ΔeT/eT • select “Cone-Radius” and “threshold” with better resolution 100GeV Jet 0-10% 30-40% 60-75% Cone-Radius Threshold[GeV]

  9. Min-eT, eTseed Nreal : # of foundBack-to-Back Jetsfrom PYTHIA Dijet Nfound : # of found Back-to-Back Jets by CellJet’ Nembed : # of embeddedDiJet (1) • S/(S+B) ≡ Nreal/Nfound • efficiency ≡ Nreal/Nembed Select “Min-eT” and “eTseed” with better S/(S+B)*efficiency definition of Back-to-Back Jet |dφ-π|<0.3 Comparison with PYTHIA-Jets distance btw embedded jet and found jet < 0.15 |eTpythia jet-eTfound jet|/eTpythia jet < 0.45 0-10% 50-100GeV S/(S+B) efficiency S/(S+B)*effciency In other centrality and other energy, the same trend is seen.

  10. parameter setting 50GeV Jet configuration eT-seed & Min-eT should be constant

  11. Energy Resolution Single Jet Energy Resolution Parton Energy Resolution compare found Jet eT with primary parton eT • compare found Jet eT with embeded Jet eT 30%(central) 17%(peripheral) 25%(central) 12%(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

  15. coplanarity R=0.2 R=1.0

  16. energy balance R=0.2 R=1.0

  17. 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

  20. 60-75% 40-50% 20-30% 0-10% 50GeV threshold, coneRadius 100GeV Cone-Radius 150GeV Threshold[GeV]

  21. 0-10% 20-30% 40-50% 60-75% 50~100GeV Min-eT, eTseed 100~150GeV eTseed/Min-eT 150~200GeV Min-eT/pTHat

  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.

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