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Jet hadrochemistry. PYTHIA vs HERWIG

Jet hadrochemistry. PYTHIA vs HERWIG. Sergey Kiselev, ITEP Moscow for the TOF group Motivation Input info/assumptions Jet finder for γ -jet CDF events STAR events LHC events Summary and next steps. Motivation. EPJ C55, 293 (2008). Medium modifications of jet hadrochemistry in AA

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Jet hadrochemistry. PYTHIA vs HERWIG

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  1. Jet hadrochemistry. PYTHIA vs HERWIG • Sergey Kiselev, ITEP Moscow for the TOF group • Motivation • Input info/assumptions • Jet finder for γ-jet • CDF events • STAR events • LHC events • Summary and next steps PWG4 meeting, CERN S.Kiselev

  2. Motivation EPJ C55, 293 (2008) Medium modifications of jet hadrochemistry in AA (S.Sapeta, U.A.Wiedemann EPJ, C55, 293 (2008)) There are theoretical speculations (K.Werner, C.Pajares HIF 19.10.09) that at LHC energies “medium”/”collective state” can be created in high-multiplicity pp events The goal: jet hadrochemistry for γ-jet process in pp events PWG4 meeting, CERN S.Kiselev

  3. Input info/assumptions - PYTHIA6.420 and HERWIG6.510 generators: - prompt γ production, PYTHIA: MSEL = 10 HERWIG: IPROC=1800 - PDF:kCTEQ5L - [PTMIN, PTMAX] window - “ECAL/PHOS trigger”: γ in |η|<0.1 with pT in [PTMIN,PTMAX] - Barrel region |η|<1, pT > 0.5 GeV/c (to reach TOF) - π0 decays are switched off - “trigger” events (~104 per a set): - “CDF”: pbap+p @1.8 TeV, [PTMIN,PTMAX]=[100,120] GeV/c - “STAR”: p+p @ 200 GeV, [PTMIN,PTMAX]= [10,15] ,[15,20] ,[20,50] GeV/c, KS , Λ decays are switched off - “LHC”: p+p @ 200 GeV, [PTMIN,PTMAX]= [40,60] GeV/c PWG4 meeting, CERN S.Kiselev

  4. Jet finder for γ-jet An idea: to explore γ info in a jet finder, pTjet ≈ pTγ The algorithm: - step 0: selecting particles with the projection sγ ≡(pT , -pTγ) > 0 - step 1: ordering them on sγ decrease adding particles to a jet until | pTjet - pTγ |/pTγ < ε (=10%) - step 2: the same as step 1 but ordering on sjet ≡(p , pjet), where pjet was defined in the step 1, … until | pTjet - pTγ | < pTcut (= 2 GeV/c) No need to use a cut on cone parameters R=√(Δϕ2 +Δη2 ), θc → → → → → → → → → → → PWG4 meeting, CERN S.Kiselev

  5. An example: “CDF” events step 1  ~ 50% of events, step 2  ~ 10% of events. R < 0.5  ~ 40% R < 1.0  ~ 60% of jets unchanged PWG4 meeting, CERN S.Kiselev

  6. “CDF” events – kT spectrum PR D68, 012003 (2003) Both generators demonstrate a reasonable shape of the kT spectrum PWG4 meeting, CERN S.Kiselev

  7. “CDF” events – ξ spectrum PR D68, 012003 (2003) Reasonable agreement with the data (θc cut remove soft particles) More soft particles in the HERWIG jet PWG4 meeting, CERN S.Kiselev

  8. GEANT codes 1. γ 16. KS 2. e+ 17. η 3. e- 18. Λ 4. ν 19. Σ+ 5. µ+ 20. Σ0 6. µ- 21. Σ- 7. π0 22. Ξ0 8. π + 23. Ξ- 9. π - 24. Ω- 10. KL 25. n 11. K+ 26. Λ 12. K- 27. Σ+ 13. n 28. Σ0 14. p+ 29. Σ- 15. p- 30. Ξ0 Jet composition in “CDF” events HERWIG6.420: mult(p) > mult(K) ??? I suspect it is because the Herwig fragmentation function for jets into protons is not reliable.  You should try Herwig++.Best, Bryan PWG4 meeting, CERN S.Kiselev

  9. “STAR” events – ξ spectra of KS and Λ EPJ C61, 769 (2009) Data: an inverse mass ordering of ξ0(the peak value) for strange particles ξ0 (Λ) > ξ0 (KS), dN/dξmax(Λ) ≈ dN/dξmax(KS) Generators: do not reproduce both the facts ξ0HERWIG > ξ0PYTHIA PWG4 meeting, CERN S.Kiselev

  10. “STAR” events – ξ spectra of KS and Λ PWG4 meeting, CERN S.Kiselev

  11. “LHC” events (Ejet ~50 GeV):PYTHIA vsHERWIG PWG4 meeting, CERN S.Kiselev

  12. gluon jet “LHC” PYTHIAevents(Ejet ~50 GeV): gluon vs quark jet quark jet PWG4 meeting, CERN S.Kiselev

  13. Summary and next steps • The jet finder algorithm for the γ–jet process in pp events • has been proposed. • PYTHIA, and HERWIG agree reasonably with the CDF and • STAR data for charged hadron kT and ξ distributions • PYTHIA and HERWIG do not reproduce the STAR data: • inverse mass ordering of ξ0, dN/dξmax(Λ) ≈ dN/dξmax(KS) • ξ0HERWIG > ξ0PYTHIA • HERWIG6.420: in a jet mult(p) > mult(K) • Next steps: • - implement the jet finder into the AliRoot package • - prepare/test a jet analysis task for the γ–jet process in pp PWG4 meeting, CERN S.Kiselev

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