1. 16.11.2009PWG4 meeting, CERN S.Kiselev 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

2. Motivation 16.11.2009PWG4 meeting, CERN S.Kiselev 2 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 EPJ C55, 293 (2008)

3. Input info/assumptions 16.11.2009PWG4 meeting, CERN S.Kiselev 3 - 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 p T in [PTMIN,PTMAX] - Barrel region |η| 0.5 GeV/c (to reach TOF) - π 0 decays are switched off - “trigger” events (~10 4 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, K S, Λ decays are switched off - “LHC”: p+p @ 200 GeV, [PTMIN,PTMAX]= [40,60] GeV/c

4. Jet finder for γ-jet 16.11.2009PWG4 meeting, CERN S.Kiselev 4 An idea: to explore γ info in a jet finder, p T jet ≈ p T γ The algorithm: - step 0: selecting particles with the projection s γ ≡(p T, -p T γ ) > 0 - step 1: ordering them on s γ decrease adding particles to a jet until | p T jet - p T γ |/p T γ < ε (=10%) - step 2: the same as step 1 but ordering on s jet ≡(p, p jet ), where p jet was defined in the step 1, … until | p T jet - p T γ | < p T cut (= 2 GeV/c) No need to use a cut on cone parameters R=√(Δ ϕ 2 +Δη 2 ), θ c → →→ →→ →→ →→ → →

5. An example: “CDF” events 16.11.2009PWG4 meeting, CERN S.Kiselev 5 R < 0.5  ~ 40% R < 1.0  ~ 60% of jets unchanged step 1  ~ 50% of events, step 2  ~ 10% of events.

6. “CDF” events – k T spectrum 16.11.2009PWG4 meeting, CERN S.Kiselev 6 PR D68, 012003 (2003) Both generators demonstrate a reasonable shape of the k T spectrum

7. “CDF” events – ξ spectrum 16.11.2009PWG4 meeting, CERN S.Kiselev 7 PR D68, 012003 (2003) Reasonable agreement with the data (θ c cut remove soft particles) More soft particles in the HERWIG jet

8. Jet composition in “CDF” events 16.11.2009PWG4 meeting, CERN S.Kiselev 8 GEANT codes 1. γ 16. K S 2. e+ 17. η 3. e- 18. Λ 4. ν 19. Σ+ 5. µ+ 20. Σ0 6. µ- 21. Σ- 7. π 0 22. Ξ0 8. π + 23. Ξ- 9. π - 24. Ω- 10. K L 25. n 11. K+ 26. Λ 12. K- 27. Σ+ 13. n 28. Σ0 14. p+ 29. Σ- 15. p- 30. Ξ0 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

9. “STAR” events – ξ spectra of K S and Λ 16.11.2009PWG4 meeting, CERN S.Kiselev 9 EPJ C61, 769 (2009) Data: an inverse mass ordering of ξ 0 (the peak value) for strange particles ξ 0 (Λ) > ξ 0 (K S ), dN/dξ max (Λ) ≈ dN/dξ max (K S ) Generators: do not reproduce both the facts ξ 0 HERWIG > ξ 0 PYTHIA

10. “STAR” events – ξ spectra of K S and Λ 16.11.2009PWG4 meeting, CERN S.Kiselev 10

11. “LHC” events (E jet ~50 GeV): PYTHIA vs HERWIG 16.11.2009PWG4 meeting, CERN S.Kiselev 11

12. “LHC” PYTHIA events (E jet ~50 GeV): gluon vs quark jet 16.11.2009PWG4 meeting, CERN S.Kiselev 12 gluon jet quark jet

13. Summary and next steps 16.11.2009PWG4 meeting, CERN S.Kiselev 13 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 ξ 0, dN/dξ max (Λ) ≈ dN/dξ max (K S ) ξ 0 HERWIG > ξ 0 PYTHIA 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