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Interjet Energy Flow in PHP

Interjet Energy Flow in PHP. Patrick Ryan University of Wisconsin Claire Gwenlan Oxford University June 10, 2005. ZEUS Collaboration Meeting DESY. Use pQCD to study diffraction Hard Diffractive PHP Hard: High E T Jets (E T > 5 GeV) Diffractive: Gap between jets

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Interjet Energy Flow in PHP

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  1. Interjet Energy Flow in PHP Patrick Ryan University of Wisconsin Claire Gwenlan Oxford University June 10, 2005 ZEUS Collaboration Meeting DESY

  2. Use pQCD to study diffraction Hard Diffractive PHP Hard: High ET Jets (ET > 5 GeV) Diffractive: Gap between jets Photoproduction: Q2 ~ 0 Rapidity Gap Topology Distance between jet centers: Dh ETGap = Total ET between leading and trailing jets Gap Event: ETGap < ETCut Gap indicates color singlet exchange Rapidity Gap Events q t 2p g Remnant f Leading Jet Dijet Events with large Rapidity separation and ETGap < ETCut Gap ET Trailing Jet p Remnant 0 -2.4 h 2.4 All Dijet Events with large Rapidity separation

  3. Simulation of gp EventsZEUS - AMADEUS • PYTHIA 6.1 and HERWIG 6.1 MC • Direct and Resolved MC generated separately • Resolved MC includes Multi Parton Interactions • Dir and Res combined by fitting xg distributions to data • Color Singlet Exchange MC • HERWIG: BFKL • Uses BFKL Pomeron as exchange object in Rapidity Gap events • PYTHIA: High-t g • Purpose is simply to match the data • Note: Rapidity Gap not due to photon exchange

  4. ZEUS 96-97 Data Luminosity: 38 pb-1 Offline Cleaning Cuts |zvtx| < 40 cm No Sinistra95 e+ with Pe > 0.9, Ee > 5 GeV, ye < 0.85 0.2 < yjb < 0.85 Dijet Selection ET1,2 > 5.1, 4.25 GeV |h1,2| < 2.4 ½|h1 + h2| < 0.75 [(Spx)2 + (Spy)2] / SET < 2 GeV1/2 2.5 < |h1 - h2| < 4.0  Gap Definition 4 Gap Samples ETCUT = 0.6, 1.2 1.8, 2.4 GeV Different Gap ET HPP Trigger FLT Slot 42 SLT HiEt I/II/III TLT HPP14 (DST bit 77) ~70,000 Inclusive Events Event Selection and xgOBS Fitting HERWIG xgOBSFit to Data Direct + Resolved Direct PYTHIA: 30% Direct + 70% Resolved HERWIG: 44% Direct + 56% Resolved (Using Tuned HERWIG/PYTHIA - see later slides) Mixing used to correct data to had level

  5. Gap ET Cross Section Default ZEUS PYTHIA & HERWIG HERWIG PYTHIA • Default MC • Used to unfold data • Plotted vs. Data • MC does not describe data at large Gap ET (region with no CS) • Need good agreement at High Gap ET to establish depletion at Low Gap ET

  6. Large Systematic Differences Default PYTHIA & HERWIG Data Corrected with PYTHIA & HERWIG • Large Sys Differences • Large Systematic Errors • Tuning Procedure • Match unfolded data and HZTOOL prediction in Highest 3 Gap ET bins • Region without CS contribution • Generate AMADEUS using tuned parameters

  7. PYTHIA Tuning • Default ZEUS PYTHIA 6.1 • Proton PDF: GRV94, LO (Set 5) • Photon PDF: SaS2D (Set 3 of SaSph) • pTMin 1= 2.0 • pTMin 2= 1.5 • Modified (Tuned) PYTHIA 6.1 • Proton PDF: CTEQ 5L (Set 46) • Photon PDF: SaS2D (Set 3 of SaSph) • pTMin 1= 1.9 • pTMin 2= 1.7 pTMin 1: pT of Hardest interaction pTMin2: pT of all secondary interactions

  8. HERWIG Tuning • Default ZEUS HERWIG 6.1 • Proton PDF: GRV94 LO (Set 5) • Photon PDF: WHIT-G 2 • Factor to reduce proton radius: 1.0 • Probability of Soft Underlying Event: 1.0 • PTMIN1 = 1.8 GeV • Modified (Tuned) HERWIG 6.1 • Proton PDF: CTEQ 5L (Set 46 of CTEQ) • Photon PDF SaS2D (Set 3 of SaSph) • Factor to reduce proton radius: 3.0 • Probability of Soft Underlying Event: 0.03 • PTMIN1 = 2.7 GeV

  9. Kinematic Variables - HERWIG Default HERWIG Tuned HERWIG • Tuned HERWIG gives better description of Data than default HERWIG

  10. Kinematic Variables – PYTHIA Default PYTHIA Tuned PYTHIA • Tuned PYTHIA gives comparable description of Data • Now have two MCs that describe data well

  11. Gap ET Cross SectionTuned PYTHIA and HERWIG • Reduced systematic difference between HERWIG & PYTHIA • Large Gap ET well described • Unfolding with CS changes cross section in low Gap ET bins ~10% • Color Singlet Contributions • PYTHIA: 3.1% HERWIG 3.8% Unfolded without CS Unfolded with CS Only stat errors

  12. Gap Fraction Inclusive Cross Section (s Inc ) Gap Cross Section (sGap) ETGap < 1.0 GeV Gap Fraction = sGap / sInc MC + CS gives good description of data

  13. Old vs. New Results Preliminary ICHEP 2002 New Results (P.R. and C.G.) • New Results: Better description of data at large Dh • Improves confidence in CS extraction

  14. Comparison Between P.R & C.G Gap ET Delta Eta Data unfolded with PYTHIA without CS Excellent agreement between analyses

  15. Interjet Energy Flow Summary • Conclusions • Tuned HERWIG & PYTHIA both describe data well • High Gap ET well described • Reduced systematic difference between data unfolded with HERWIG and PYTHIA • Gap ET & Dh Cross Section well described • Evidence of 3-4%Color Singlet Exchange contribution • Excellent agreement between P.R. and C.G. analyses • Plans • Finish systematics • Complete comparison of analyses • Make results preliminary for EPS • Write paper

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