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Interjet Energy Flow

Interjet Energy Flow. Patrick Ryan University of Wisconsin Claire Gwenlan Oxford University Oct. 20, 2004. ZEUS Collaboration Meeting Padova, Italy. Hard Diffractive g p. Use pQCD to study diffraction Hard Diffractive Photoproduction Hard: High E T Jets (E T > 5 GeV)

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Interjet Energy Flow

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  1. Interjet Energy Flow Patrick Ryan University of Wisconsin Claire Gwenlan Oxford University Oct. 20, 2004 ZEUS Collaboration Meeting Padova, Italy

  2. Hard Diffractive gp • Use pQCD to study diffraction • Hard Diffractive Photoproduction • Hard: High ET Jets (ET > 5 GeV) • Diffractive: Gap btw. jets, small momentum transfer at P vertex • Photoproduction: Q2 ~ 0 Standard Diffraction Hard Diffractive gp q Rapidity Gap t

  3. Topology of Rapidity Gaps 2p g Remnant Leading Jet f Leading Trailing Jet Jet Gap g Remnant Trailing 3 Jet 2p 0 h p Remnant f h Distance between jet centers: Dh • ETGap = Total ET between leading and trailing jets • Gap Event: ETGap < ETCut • Gap indicates color singlet exchange -2.4 2.4 0 -3

  4. The Gap Fraction All Dijet Events with Rapidity Gap Dijet Events with Rapidity Gap and ETGap < ETCut • Non-Singlet • f(Dh) decreases exponentially with Dh • Particle production fluctuations  Gap • Non diffractive exchange • Singlet • f(Dh) constant in Dh Expectation for Behavior of Gap Fraction (J.D. Bjorken, V.Del Durca, W.-K. Tung)* fGap fGapn-s fGapSinglet 2 4 3 *Phys. Rev. D47 (1992) 101 Phys Lett. B312 (1993) 225

  5. Simulation of gp Events • 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 (next slide) • PDFs • PDF(p): GRV-LO • PDF(g): WHIT 2 • Color Singlet Exchange MC • PYTHIA: High-t g • Purpose is simply to match the data • Note: Rapidity Gap not due to photon exchange • HERWIG: BFKL • Uses BFKL Pomeron as exchange object in Rapidity Gap events

  6. 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 Jet Selection ET1,2 > 5.1, 4.25 GeV (ZUFO) |h1,2| < 2.4 ½|h1 + h2| < 0.75 [(Spx)2 + (Spy)2] / SET < 2 GeV1/2 2.5 < |h1 - h2| < 4.0 4 Gap Samples ETCUT = 0.6, 1.2 1.8, 2.4 GeV (ZUFO) HPP Trigger FLT Slot 42 SLT HiEt I/II/III TLT HPP14 (DST bit 77) ~70,000 Inclusive Events Event Selection and xg Fitting xgFit to Data Direct + Resolved Direct 46% Direct + 54% Resolved Mixing used in all calculations

  7. Energy in the Gap PYTHIA HERWIG • Addition of CS MC gives better agreement at low ETGap • Enough CS added to match Data in lowest bin • HERWIG agrees better than PYTHIA with data (used in next plots) • Will investigate tuning of MC input parameters (especially pT) 2.6% Color Singlet 4.8% Color Singlet

  8. Inclusive and Gap Cross Sections Compare gp Data to HERWIG Error bars show statistical errors only Inclusive  C. Gwenlan Addition of 4.8% color singlet MC improves agreement with data ETGap < 1.0 GeV Gap Fraction: Ratio of above plots

  9. Gap Fractions for Different Gap ET ETGap < 0.5 GeV ETGap < 1.0 GeV • Observed excess of Data over MC without CS exchange • Data has better agreement for MC (95.2%) + CS (4.8%) than without CS • Suggests presence of CS exchange ETGap < 1.5 GeV ETGap < 2.0 GeV

  10. Systematics – P. Ryan ETCut = 1GeV • Order of Variables • +/- 1s: ET1,ET2,h1,h2, ½|h1+h2|,Dh,YJB,pT/ET1/2,ye,Zvtx,ETCut • +/- 3%: ET and YJB (Cal Energy Scale) Very Low MC statistics for -ETCut

  11. Systematics – C. Gwenlan Gap Cross Section Gap Fraction 0.1 0.1 • Last 2 points are Cal Energy Scale • General agreement btw. analyses (except for Gap ET) ET = 1 GeV ET = 1 GeV Dh Dh

  12. H1 gp Rapidity Gap Results • Consistent with ZEUS within errors • 6.6 pb-1 of Lumi • PYTHIA • Scaled by 0.7 to matchdijet gp cross section • High-t g Exchange • Scaled by 1200 • Not candidate for observed excess in data • HERWIG • Scaled by 1.2 to match dijet gp cross section • BFKL Pomeron exchange • BFKL sample scaled by 0.8and added to gp sample

  13. Summary on gp with Rap Gap • Conclusions • HERWIG + BFKL and PYTHIA + High-t g describe data • Evidence for Color Singlet Exchange • 3-5% of CSE added to data improves match at high Dh • Good Agreement between analyses (P.R & C.G) • ZEUS results consistent with H1 within errors • Next steps • Include 98-2000 Data • Study properties of color singlet exchange • Paper in a few months

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