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Activities of the Monte Carlo Working Group (II)

Activities of the Monte Carlo Working Group (II). Convenors: P. Bartalini, S.Chekanov, S. Gieseke, F. Krauss. Multiple Parton Interactions, Underlying Events, etc. - Joint Sessions with Multi-jet final states and Energy flows MC Tuning & Validation MC Steering, Comparison & Fitting Tools.

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Activities of the Monte Carlo Working Group (II)

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  1. Activities of the Monte Carlo Working Group (II) Convenors: P. Bartalini, S.Chekanov, S. Gieseke, F. Krauss • Multiple Parton Interactions, Underlying Events, etc. - Joint Sessions with Multi-jet final states and Energy flows • MC Tuning & Validation • MC Steering, Comparison & Fitting Tools Paolo Bartalini (NTU)

  2. A lot of emphasis on the reconstruction of soft tracks! Paolo Bartalini (NTU)

  3. UE: measurement plan at the LHC Jet #1 Direction Δφ “Toward” “Transverse” “Transverse” “Away” “Away” Region From charged jet (using MB and jet triggers) 2 “Transverse” Region Topological structure of p-p collision from charged tracks Charged jet definition: ICA with mass-less charged tracks as inputThe leading The Charged jet defines a direction in the f plane The transverse region is particularly sensitive to the UE “Toward” Region jet1  “Transverse” Region “Away” Region Main observables: + dN/dhdf, charged density + d(PTsum)/dhdf, energy density 0 -2 2  From D-Y muon pair production (using muon triggers) observables are the same but defined in all the f plane (after removing the m pairs everything else is UE) The PT of the boson may be used to define a direction Paolo Bartalini (NTU)

  4. + Pythia Tune DW (=.125) OLD MPI, IP CORRELATIONS, ~ TUNE A + Pythia Tune DWT (=0.08) DW with default PT-cut-off evolution + Pythia Tune S0 (=0.08) P.Skands, New MPI, colour-flow All these Pythia tunes describe MB & UE at Tevatron. -> Paolo Bartalini (NTU)

  5. CMS Preliminary CMS Preliminary ∫ L dt = 100 pb-1 ∫ L dt = 100 pb-1 (input to RECO is DWT) UE in jets: Ratios in the transverse region • Ratios between uncorrected UE-observables: • UE-density(pT(track) > 0.9 GeV/c) / UE-density(pT(track) > 1.5 GeV/c) • No additional track reconstruction corrections needed! • track reconstruction performance uniform in pT for pT > 0.9 GeV/c CMS Physics Analysis Summary QCD-07-003 → discriminate DW/DWT against S0 Paolo Bartalini (NTU)

  6. [Z.Rurikova] Paolo Bartalini (NTU)

  7. Jimmy Tune: Charged Multiplicity OK, Softer PT spectrum Paolo Bartalini (NTU)

  8. New UE Model in Herwig++ [M.Bähr] Description of Tevatron UE phenomenology Similar predictions with respect to the Pythia tunes at the LHC energy (Energy dependency of the cut-offs) Paolo Bartalini (NTU)

  9. The goal is to produce data (corrected to the particle level) that can be used by the theorists to tune and improve the QCD Monte-Carlo models that are used to simulate hadron-hadron collisions. Paolo Bartalini (NTU)

  10. Now it would be interesting to compare with reference tunes adopting the new Pythia MPIs. See [P.Skands, D.Wielke, hep/ph 0703081] Paolo Bartalini (NTU)

  11. Observable: track multiplicity as a function of  and Pt Jet in bins of Xγ. Paolo Bartalini (NTU)

  12. “MI long CC”: Default but PARP (85) = 0.33 “MI short CC2NN”: Default but PARP (85) & PARP (86) “changed” (preferred ?) Paolo Bartalini (NTU)

  13. Study of hard Multiple Parton Interactions Cross section: Preliminary additional jets from PS LHC Same sign W. Single int. additional jets from MI Same sign W. Double int. [D.Treleani] [F.Bechtel] Where sinel = ssoft + sH “S” = Single Interactions, “D” = Double Interactions, “H” = Hard seff(PT) contains the information on the spatial distribution of partons Count the interactions (e.g. mini-jets), quote the momenta of Nint Paolo Bartalini (NTU)

  14. Pythia 8.1 - physics ~ Pythia 6.4 Tune S0 Herwig++ 2.2 - MPI along the lines of Jimmy Need double-parton component to describe the data Paolo Bartalini (NTU)

  15. Bottom Line on MPI • Huge progress seen in the last two years • Refinement of the existing models • Implementation in most of the new reference MCs: Pythia 8, Herwig++, Sherpa,… • New ideas for the future: dynamical structure of the hadrons, connection to diffraction • Much More data avaliable to constraint the models • CDF UE in Jets, Drell-Yan, MB <PT> vs Nch etc. • Converging on HERA results • New Tunes • Wide spectrum of LHC feasibility studies in both the soft and hard regimes • Didn’t mention Today: eff measurement with mini-jets • This section of the proceedings looks promising! Paolo Bartalini (NTU)

  16. MC Steering, Comparison & Fitting Tools Paolo Bartalini (NTU)

  17. Paolo Bartalini (NTU)

  18. [A. Buckley] Paolo Bartalini (NTU)

  19. [A. Buckley] Paolo Bartalini (NTU)

  20. Professor: the tuning tool [A. Buckley] Paolo Bartalini (NTU)

  21. PDF4MC [H.Jung] Paolo Bartalini (NTU)

  22. PDF4MC [H.Jung] Paolo Bartalini (NTU)

  23. PDF4MC [H.Jung] Paolo Bartalini (NTU)

  24. An approach to fast fits of the uPDF[A.Knutsson] Paolo Bartalini (NTU)

  25. Thanks to all the contributorsof WG5Most of you will be approached in the next weeks in order to contribute to the proceedings Paolo Bartalini (NTU)

  26. Backup Paolo Bartalini (NTU)

  27. pQCD Models The Pythia solution: [T. Sjöstrand et al. PRD 36 (1987) 2019] Multiple Parton Interactions (MPI) (now available in other general purpose MCs: Herwig/Jimmy, Sherpa, etc.) ISR, FSR, SPECTATORS… Not enough to account for the observed multiplicities & PT spectra  Inspired by observations of double high PT scatterings Main Parameter: PT cut-off PT0 (dampening) • Cross Section Regularization for PT 0 • PT0 can be interpreted as inverse of effective colour screening length • Controls the number of interactions hence the Multiplicity: < Nint > = sparton-parton /sproton-proton Tuning for the LHC: Emphasis on the Energy-dependence of the parameters. Paolo Bartalini (NTU)

  28. Extrapolation to the LHC Energy 2e æ ö s ç ÷ = LHC P P ç ÷ 0 0 T T 14 TeV è ø MB: Average Charged Multiplicity (Central Region) • UA5 at s = 53, 200, 546, 900 GeV [Z. Phys. C 33 (1986) 1] • CDF at s = 630, 1800 GeV [PRD 41 (1989) 2330] • “post Hera” PDFs have increased color screening at low x ? x g(x,Q2)  x- for x  0 • PT cut-off adjusted to reproduce the measured multiplicity for each PDF • PT cut-off fitted with exponential function NSD CTEQ4L Paolo Bartalini (NTU)

  29. Side Note on the energy dependency of the PT cut-off G.Gustafson & G.Miu rather suggest energy independency of the PT cut-off. Minijets and transverse energy flow in high-energy collisions. [Phys.Rev.D63:034004,2001] Hadronic collisions in the linked dipole chain model. [Phys.Rev.D67:034020,2003] Paolo Bartalini (NTU)

  30. Total Color octet Color-singlet CTEQ6L|y|<0.6 pT0=2.85 GeV nice agreement Quarkonia also prefers dampening... Phys. Rev. D71: 032001, 2005 NRQCD PYTHIA Total Color octet Color-singlet NRQCD PYTHIA CTEQ6L|y|<0.6 CDF data • disagreement at low PT [M.Bargiotti] [M.Bargiotti] Regularization natural: gluon exchange in the t channel d/dPT2 ~ 1/ dPT4 Let’s assume universality: same PT0 of MPI, same energy dependency! Paolo Bartalini (NTU)

  31. Pythia Tunes PT0= PT0(Ecm/E0)PARP(90) Paolo Bartalini (NTU)

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