Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 1

Patrick Ryan University of Wisconsin

Claire GwenlanOxford University

June 10, 2005

Interjet Energy Flow in PHPInterjet Energy Flow in PHPInterjet Energy Flow in PHPInterjet Energy Flow in PHP

ZEUS Collaboration Meeting

DESY

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 2

Rapidity Gap EventsRapidity Gap EventsRapidity Gap EventsRapidity Gap Events

•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: • ET

Gap = Total ET between leading and trailing jets

• Gap Event: ETGap < ET

Cut

• Gap indicates color singlet exchange

t

q

Jet

Jet

Gap

Remnant

0

2

-2.4 2.4

Trailing

Leading

p Remnant

dd

ddf Gap

/

/)(

Dijet Events with large Rapidity separation and ET

Gap < ETCut

All Dijet Events with large Rapidity separation

ET

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 3

Simulation of Simulation of p Eventsp EventsZEUS - AMADEUSZEUS - AMADEUS

Simulation of Simulation of p Eventsp EventsZEUS - AMADEUSZEUS - 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 xdistributions 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

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 4

Event Selection and xEvent Selection and xOBSOBS Fitting FittingEvent Selection and xEvent Selection and xOBSOBS Fitting Fitting

•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• ET

1,2 > 5.1, 4.25 GeV • || < 2.4• ½|| < 0.75• [(px)2 + (py)2] / ET < 2 GeV1/2 • 2.5 < || < 4.0 Gap Definition

•4 Gap Samples• ET

CUT = 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

Direct

Direct + Resolved

HERWIG xOBS

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

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 5

Gap EGap ETT Cross Section Cross Section Default ZEUS PYTHIA & HERWIG Default ZEUS PYTHIA & HERWIG

Gap EGap ETT Cross Section Cross Section Default ZEUS PYTHIA & HERWIG Default ZEUS PYTHIA & HERWIG

PYTHIA HERWIG

•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

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 6

Large Systematic Differences Large Systematic Differences Default PYTHIA & HERWIGDefault PYTHIA & HERWIG

Large Systematic Differences Large Systematic Differences Default PYTHIA & HERWIGDefault 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

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 7

PYTHIA TuningPYTHIA TuningPYTHIA TuningPYTHIA 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 pT

Min 1: pT of Hardest interaction

pTMin 2: pT of all secondary interactions

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 8

HERWIG TuningHERWIG TuningHERWIG TuningHERWIG 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• PT

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• PT

MIN1 = 2.7 GeV

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 9

Kinematic Variables - HERWIGKinematic Variables - HERWIGKinematic Variables - HERWIGKinematic Variables - HERWIG

•Tuned HERWIG gives better description of Data than default HERWIG

Default HERWIG Tuned HERWIG

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 10

Kinematic Variables – PYTHIAKinematic Variables – PYTHIAKinematic Variables – PYTHIAKinematic Variables – PYTHIA

Default PYTHIA Tuned PYTHIA

• Tuned PYTHIA gives comparable description of Data • Now have two MCs that describe data well

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 11

Gap EGap ETT Cross Section Cross SectionTuned PYTHIA and HERWIGTuned PYTHIA and HERWIG

Gap EGap ETT Cross Section Cross SectionTuned PYTHIA and HERWIGTuned 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

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 12

Gap FractionGap Fraction Gap FractionGap Fraction

•MC + CS gives good description of data

Inclusive Cross Section (Inc )

Gap Cross Section (Gap)

ETGap < 1.0 GeV

Gap Fraction = Gap / Inc

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 13

Old vs. New ResultsOld vs. New ResultsOld vs. New ResultsOld vs. New ResultsPreliminary ICHEP 2002 New Results (P.R. and C.G.)

•New Results: Better description of data at large •Improves confidence in CS extraction

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 14

Comparison Between P.R & C.GComparison Between P.R & C.GComparison Between P.R & C.GComparison Between P.R & C.G

Gap ET Delta Eta

•Data unfolded with PYTHIA without CS

•Excellent agreement between analyses

Interjet Energy Flow . Patrick Ryan, Univ. of Wisconsin Collaboration Meeting , June 6, 2005 - 15

Interjet Energy Flow SummaryInterjet Energy Flow SummaryInterjet Energy Flow SummaryInterjet 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 & 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