1. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 1 Patrick Ryan University of Wisconsin Claire Gwenlan Oxford University June 10, 2005 Interjet Energy Flow in PHP ZEUS Collaboration Meeting DESY

2. Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting, Oct.. 15, 2003 - 2 Rapidity Gap Events Use pQCD to study diffraction Hard Diffractive PHP Hard: High E T Jets (E T > 5 GeV) Diffractive: Gap between jets Photoproduction: Q 2 ~ 0 Rapidity Gap Topology Distance between jet centers:  E T Gap = Total E T between leading and trailing jets Gap Event: E T Gap < E T Cut Gap indicates color singlet exchange t q Jet Gap  Remnant 0 22  -2.42.4 Trailing Leading p Remnant  Dijet Events with large Rapidity separation and E T Gap < E T Cut All Dijet Events with large Rapidity separation ETET

3. Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting, Oct.. 15, 2003 - 3 Simulation of  p Events ZEUS - 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 x  distributions to data Color Singlet Exchange MC HERWIG: BFKL Uses BFKL Pomeron as exchange object in Rapidity Gap events PYTHIA: High-t  Purpose is simply to match the data Note: Rapidity Gap not due to photon exchange

4. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 4 Event Selection and x  OBS Fitting ZEUS 96-97 Data Luminosity: 38 pb -1 Offline Cleaning Cuts |z vtx | < 40 cm No Sinistra95 e + with P e > 0.9, E e > 5 GeV, y e < 0.85 0.2 < y jb < 0.85 Dijet Selection E T 1,2 > 5.1, 4.25 GeV |   | < 2.4 ½|     | < 0.75 [(  p x ) 2 + (  p y ) 2 ] /  E T < 2 GeV 1/2 2.5 < |     | < 4.0  Gap Definition 4 Gap Samples E T CUT = 0.6, 1.2 1.8, 2.4 GeV Different Gap E T HPP Trigger FLT Slot 42 SLT HiEt I/II/III TLT HPP14 (DST bit 77) ~70,000 Inclusive Events Direct Direct + Resolved HERWIG x  OBS Fit to Data 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. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 5 Gap E T Cross Section Default ZEUS PYTHIA & HERWIG PYTHIA HERWIG Default MC Used to unfold data Plotted vs. Data MC does not describe data at large Gap E T (region with no CS) Need good agreement at High Gap E T to establish depletion at Low Gap E T

6. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 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 E T bins Region without CS contribution Generate AMADEUS using tuned parameters

7. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 7 PYTHIA Tuning Default ZEUS PYTHIA 6.1 Proton PDF: GRV94, LO (Set 5) Photon PDF: SaS2D (Set 3 of SaSph) p T Min 1 = 2.0 p T Min 2 = 1.5 Modified (Tuned) PYTHIA 6.1 Proton PDF: CTEQ 5L (Set 46) Photon PDF: SaS2D (Set 3 of SaSph) p T Min 1 = 1.9 p T Min 2 = 1.7 p T Min 1 : p T of Hardest interaction p T Min 2 : p T of all secondary interactions

8. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 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 P T MIN1 = 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 P T MIN1 = 2.7 GeV

9. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 9 Kinematic Variables - HERWIG Tuned HERWIG gives better description of Data than default HERWIG Default HERWIG Tuned HERWIG

10. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 10 Kinematic Variables – PYTHIA Default PYTHIATuned PYTHIA Tuned PYTHIA gives comparable description of Data Now have two MCs that describe data well

11. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 11 Gap E T Cross Section Tuned PYTHIA and HERWIG Reduced systematic difference between HERWIG & PYTHIA Large Gap E T well described Unfolding with CS changes cross section in low Gap E T bins ~10% Color Singlet Contributions PYTHIA: 3.1% HERWIG 3.8% Unfolded without CS Unfolded with CS Only stat errors

12. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 12 Gap Fraction Gap Fraction MC + CS gives good description of data Inclusive Cross Section (  Inc ) Gap Cross Section (  Gap ) E T Gap < 1.0 GeV Gap Fraction =  Gap /  Inc

13. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 13 Old vs. New Results Preliminary ICHEP 2002 New Results (P.R. and C.G.) New Results: Better description of data at large  Improves confidence in CS extraction

14. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 14 Comparison Between P.R & C.G Gap E T Delta Eta Data unfolded with PYTHIA without CS Excellent agreement between analyses

15. Interjet Energy Flow. Patrick Ryan, Univ. of Wisconsin Collaboration Meeting, June 6, 2005 - 15 Interjet Energy Flow Summary Conclusions Tuned HERWIG & PYTHIA both describe data well High Gap E T well described Reduced systematic difference between data unfolded with HERWIG and PYTHIA Gap E T &  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