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Multiple Parton Interactions and the Underlying Event

Multiple Parton Interactions and the Underlying Event. Session I: Experiment. Rick Field University of Florida ( for the CDF & CMS Collaborations ). Some Topics. What do we know about the soft underlying event?. DESY, May 18-19 2007. Contributors.

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Multiple Parton Interactions and the Underlying Event

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  1. Multiple Parton Interactionsand the Underlying Event Session I: Experiment Rick Field University of Florida (for the CDF & CMS Collaborations) Some Topics • What do we know about the soft underlying event? DESY, May 18-19 2007 Contributors • What do we know about hard multiple interactions? • L. Marti • S. Osman • L. Joennson • J. Turnau • L. Goerlich • What about correlations? • What is needed for LHC predictions? • Monte-Carlo underlying event tunes. • What are the measurements needed to better understand MPI? • Can HERA Contribute? • What other Tevatron measurements do we need? Rick Field – Florida/CDF/CMS

  2. Bruce Knuteson Khaldoun Makhoul Georgios Choudalakis Markus Klute Conor Henderson Ray Culbertson Gene Flanagan MIT Search Scheme: Vista/Sleuth Exclusive 3 Jet Final State Challenge CDF Data At least 1 Jet (“trigger” jet) (PT > 40 GeV/c, |h| < 1.0) Normalized to 1 PYTHIA Tune A Exactly 3 jets (PT > 20 GeV/c, |h| < 2.5) R(j2,j3) Order Jets by PT Jet1 highest PT, etc. Rick Field – Florida/CDF/CMS

  3. R > 1.0 Exc3J: R(j2,j3) Normalized The data have more 3 jet events with small R(j2,j3)!? • Let Ntrig40 equal the number of events with at least one jet with PT > 40 geV and |h| < 1.0 (this is the “offline” trigger). • Let N3Jexc20 equal the number of events with exactly three jets with PT > 20 GeV/c and |h| < 2.5 which also have at least one jet with PT > 40 GeV/c and |h| < 1.0. Normalized to N3JexcFr • Let N3JexcFr = N3Jexc20/Ntrig40. The is the fraction of the “offline” trigger events that are exclusive 3-jet events. • The CDF data on dN/dR(j2,j3) at 1.96 TeV compared with PYTHIA Tune AW (PARP(67)=4), Tune DW (PARP(67)=2.5), Tune BW (PARP(67)=1). • PARP(67) affects the initial-state radiation which contributes primarily to the region R(j2,j3) > 1.0. Rick Field – Florida/CDF/CMS

  4. R < 1.0 3Jexc R(j2,j3) Normalized I do not understand the excess number of events with R(j2,j3) < 1.0. Perhaps this is related to the “soft energy” problem?? For now the best tune is PYTHIA Tune DW. • Let Ntrig40 equal the number of events with at least one jet with PT > 40 geV and |h| < 1.0 (this is the “offline” trigger). • Let N3Jexc20 equal the number of events with exactly three jets with PT > 20 GeV/c and |h| < 2.5 which also have at least one jet with PT > 40 GeV/c and |h| < 1.0. Normalized to N3JexcFr • Let N3JexcFr = N3Jexc20/Ntrig40. The is the fraction of the “offline” trigger events that are exclusive 3-jet events. • The CDF data on dN/dR(j2,j3) at 1.96 TeV compared with PYTHIA Tune DW (PARP(67)=2.5) and HERWIG (without MPI). • Final-State radiation contributes to the region R(j2,j3) < 1.0. • If you ignore the normalization and normalize all the distributions to one then the data prefer Tune BW, but I believe this is misleading. Rick Field – Florida/CDF/CMS

  5. Latest CDF Run 2 “Underlying Event” Results • Two Classes of Events: “Leading Jet” and “Back-to-Back”. • Two “Transverse” regions: “transMAX”, “transMIN”, “transDIF”. • Data Corrected to the Particle Level: unlike our previous CDF Run 2 “underlying event” analysis which used JetClu to define “jets” and compared uncorrected data with the QCD Monte-Carlo models after detector simulation, this analysis uses the MidPoint jet algorithm and corrects the observables to the particle level. The corrected observables are then compared with the QCD Monde-Carlo models at the particle level. • For the 1st time we study the energy density in the “transverse” region. The “underlying event” consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions. Craig Group and I are redoing This analysis with 1 fb-1. Hope to publish it by the end of the summer! “Transverse” region is very sensitive to the “underlying event”! New CDF Run 2 results (L= 385 pb-1): Rick Field – Florida/CDF/CMS

  6. “Transverse” ObservablesParticle and Detector Level “Leading Jet” “Back-to-Back” Rick Field – Florida/CDF/CMS

  7. “TransMAX/MIN” Nchg DensityPYTHIA Tune A vs HERWIG “Back-to-Back” “Leading Jet” • Shows the charged particle density, dNchg/dhdf, in the “transMAX” and “transMIN” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) for “Leading Jet” and “Back-to-Back” events. • Compares the (corrected) data with PYTHIA Tune A (with MPI) and HERWIG (without MPI) at the particle level. Rick Field – Florida/CDF/CMS

  8. CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L • Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune A (<pT(Z)> = 9.7 GeV/c), Tune A25 (<pT(Z)> = 10.1 GeV/c), and Tune A50 (<pT(Z)> = 11.2 GeV/c). UE Parameters ISR Parameter Vary the intrensic KT! Intrensic KT Rick Field – Florida/CDF/CMS

  9. CDF Run 1 PT(Z) Tune used by the CDF-EWK group! PYTHIA 6.2 CTEQ5L • Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune A (<pT(Z)> = 9.7 GeV/c), and PYTHIA Tune AW (<pT(Z)> = 11.7 GeV/c). UE Parameters ISR Parameters Effective Q cut-off, below which space-like showers are not evolved. Intrensic KT The Q2 = kT2 in as for space-like showers is scaled by PARP(64)! Rick Field – Florida/CDF/CMS

  10. Df Jet#1-Jet#2 Jet#1-Jet#2 Df Distribution Jet-Jet Correlations (DØ) • MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5) • L= 150 pb-1 (Phys. Rev. Lett. 94 221801 (2005)) • Data/NLO agreement good. Data/HERWIG agreement good. • Data/PYTHIA agreement good provided PARP(67) = 1.0→4.0 (i.e. like Tune A, best fit 2.5). Rick Field – Florida/CDF/CMS

  11. CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L • Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune DW, and HERWIG. UE Parameters ISR Parameters Tune DW uses D0’s perfered value of PARP(67)! Intrensic KT Tune DW has a lower value of PARP(67) and slightly more MPI! Rick Field – Florida/CDF/CMS

  12. “Transverse” Nchg Density Three different amounts of MPI! PYTHIA 6.2 CTEQ5L • Shows the “transverse” charged particle density, dN/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for PYTHIA Tune A, Tune AW, Tune DW, Tune BW, and HERWIG (without MPI). UE Parameters ISR Parameter • Shows the “transverse” charged particle density, dN/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune DW, ATLAS, and HERWIG (without MPI). Three different amounts of ISR! Intrensic KT Rick Field – Florida/CDF/CMS

  13. “Transverse” PTsum Density PYTHIA 6.2 CTEQ5L Three different amounts of MPI! • Shows the “transverse” charged PTsum density, dPT/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for PYTHIA Tune A, Tune AW, Tune DW, Tune BW, and HERWIG (without MPI). UE Parameters ISR Parameter • Shows the “transverse” charged PTsum density, dPT/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune DW, ATLAS, and HERWIG (without MPI). Three different amounts of ISR! Intrensic KT Rick Field – Florida/CDF/CMS

  14. PYTHIA 6.2 Tunes PYTHIA 6.2 CTEQ5L CDF Run 2 Data! • Shows the “transverse” charged particle density, dN/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune A, DW, ATLAS, and HERWIG (without MPI). • Shows the “transverse” charged average pT, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune A, DW, ATLAS, and HERWIG (without MPI). • Shows the “transverse” charged PTsum density, dPT/dhdf, versus PT(jet#1) for “leading jet” events at 1.96 TeV for Tune A, DW, ATLAS, and HERWIG (without MPI). Identical to DW at 1.96 TeV but uses ATLAS extrapolation to the LHC! Rick Field – Florida/CDF/CMS

  15. New PYTHIA 6.2 Tunes Use LO as with L = 192 MeV! NLO Structure Function! K-factor (T. Sjostrand) UE Parameters Tune A energy dependence! ISR Parameter Intrinsic KT Rick Field – Florida/CDF/CMS

  16. New PYTHIA 6.2 Tunes Use LO as with L = 192 MeV! NLO Structure Function! K-factor (T. Sjostrand) UE Parameters ATLAS energy dependence! ISR Parameter Intrinsic KT Rick Field – Florida/CDF/CMS

  17. New PYTHIA 6.2 Tunes • Average charged particle density and PTsum density in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) at 1.96 TeV for PY Tune DW, Tune D6, and Tune QK. Rick Field – Florida/CDF/CMS

  18. New PYTHIA 6.2 Tunes • Average charged particle density and PTsum density in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus PT(jet#1) at 14 TeV for PY Tune DWT, Tune D6T, and Tune QKT. Rick Field – Florida/CDF/CMS

  19. New PYTHIA 6.2 Tunes Numbers for pT > 0.5 GeV/c, |h| < 1. We have CTEQ6L Tune D6T and NLO PDF Tune QKT! • PseudoRapidity distribution, dN/dh, for charged particles with pT > 0.5 GeV/c at 14 TeV for PY Tune DWT, Tune D6T, and Tune QKT. Note this is “hard core” (i.e. MSEL=1, PT(hard) = 0) with no trigger and with only stable particles (i.e. MSTJ(22)=1). Tune D6T uses CTEQ6L (i.e. LHAPDF = 10042) and Tune QKT uses CTEQ6.1M (i.e. LHAPDF = 10100 or 10150 which are the same). Rick Field – Florida/CDF/CMS

  20. Tevatron LHC Summary We need to decide whether to use NLO PDF’s (i.e. Tune QWT) or whether to stick with LO PDF’s (i.e. Tune DWT or Tune D6T)! • PYTHIA Tune DW is very similar to Tune A except that it fits the CDF PT(Z) distribution and it uses the DØ prefered value of PARP(67) = 2.5 (determined from the dijet Df distribution). • PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV but uses the ATLAS energy extrapolation to the LHC (i.e. PARP(90) = 0.16). And we need to develop a procedure to validate the Tunes! • PYTHIA Tune D6 and D6T are similar to Tune DW and DWT, respectively, but use CTEQ6L (i.e.LHAPDF = 10042). • PYTHIA Tune QK and QKT uses the NLO PDF CTEQ6.1M (i.e. LHAPDF = 10100 or 10150 which are the same) and use the “K-factor” to get the right amount of MPI. I prefer QK and QKT over QW and QWT! Rick Field – Florida/CDF/CMS

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