Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 1

Patrick Ryan University of Wisconsin

Aug. 27, 2004

Interjet Energy Flow Measured in ep Interjet Energy Flow Measured in ep Collisions at ZEUSCollisions at ZEUS

Interjet Energy Flow Measured in ep Interjet Energy Flow Measured in ep Collisions at ZEUSCollisions at ZEUS

DPF 2004

Riverside, CA

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 2

HERA DescriptionHERA DescriptionHERA DescriptionHERA Description

•820/920 GeV Protons

•27.5 GeV e- or e+

•CMS Energy 300/318 GeV

• Equivalent to 50 TeV fixed target

DESY

Hamburg, Germany

H1(ep)

ZEUS (ep)

Photoproduction Event in ep Collisions

0)( 2'22 kkqQVirtuality of Photon

kp

qpy

Inelasticity

e+(k)

e’(k’)

p(p)

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 3

PhotoproductionPhotoproductionPhotoproductionPhotoproduction

•Photon carries very little 4-momentum (Q2 ~ 0)•Photon is almost real•Most ep events are photoproduction

• Cross section has 1/Q4 dependence

•Direct: couples directly to a parton in proton•Resolved:

• Fluctuation of into partonic state• Parton from couples to parton in proton

General Photoproduction Direct Resolved

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 4

Diffractive Diffractive p in ep Collisionsp in ep CollisionsDiffractive Diffractive p in ep Collisionsp in ep Collisions

• Use pQCD to study diffraction in ep collisions• Hard Diffractive Photoproduction

• Hard: High ET Jets (ET > 5 GeV)• Diffractive: Gap Between jets, small momentum transfer at P

vertex• Photoproduction: Q2 ~ 0

t

q

Standard DiffractionHard Diffractive p

Rapidity Gap

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 5

Color Non-Singlet and Singlet Color Non-Singlet and Singlet Exchange in Resolved Exchange in Resolved PP

Color Non-Singlet and Singlet Color Non-Singlet and Singlet Exchange in Resolved Exchange in Resolved PP

•Color Non-Singlet Exchange:• Final state partons are color connected• Space between final state partons filled with final state particles

• No Gap between jets

•Color Singlet Exchange:• Final state partons are not color connected• Space between final state partons empty

• Rapidity Gap between jets

Color Non-Singlet Exchange Color Singlet Exchange

Jet

Jet Jet

Jet

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 6

Topology of Rapidity GapsTopology of Rapidity GapsTopology of Rapidity GapsTopology of Rapidity Gaps

Distance between jet centers: •ET

Gap = Total ET between leading and trailing jets

•Gap Event: ETGap < ET

Cut

•Gap indicates color singlet exchange

Jet

Jet

Gap

Remnant

p Remnant0

2

-2.4 2.4

Trailing

LeadingLeading Jet

Trailing Jet

Remnant

-3

3

0

2

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 7

The Gap FractionThe Gap FractionThe Gap FractionThe Gap Fraction

Expectation for Behavior of Gap Fraction (J.D. Bjorken, V.Del Durca, W.-K. Tung)*

2 3 4

fGap

fGapSinglet fGap

n-s

dd

ddf Gap

/

/)(

Singletgap

SingletNongapGap

All Dijet Events with Rapidity GapDijet Events with Rapidity Gap and ET

Gap < ETCut

•Non-Singlet• f() decreases exponentially with • Particle production fluctuations Gap• Non diffractive exchange

•Singlet• f() constant in

*Phys. Rev. D47 (1992) 101

Phys Lett. B312 (1993) 225

Rapidity Gaps. Patrick Ryan. Univ. of Wisconsin Collaboration Meeting , Oct.. 15, 2003 - 8

Simulation of Simulation of p Eventsp EventsSimulation of Simulation of p Eventsp Events

• PYTHIA 6.1 and HERWIG 6.1• Shown to match p• Use different Fragmentation and Hadronization models

• Direct and Resolved MC generated separately• Resolved MC includes Multi Parton Interactions• Dir and Res combined by fitting xdistributions to Data (coming)

• PDFs• PDF(p): GRV-LO• PDF(): WHIT 2

• Color Singlet Exchange MC• PYTHIA: High-t

• 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

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 9

Event Selection and xEvent Selection and x Fitting FittingEvent Selection and xEvent Selection and x Fitting Fitting

•ZEUS 96-97 Data• Luminosity: 38 pb-1

•Offline Cleaning Cuts• |zvtx| < 40 cm

• No e+ with Ee > 5 GeV, ye<0.85

• 0.2 < yjb < 0.85

•Jet 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

•4 Gap Samples• ET

GAP < ETCUT = 0.5, 1, 1.5, 2 GeV

•~70,000 Inclusive Events

•x: Fraction of momentum involved in collision

e

jetsT

OBS

yE

eE

x2

Direct

Direct + Resolved

x Fit to Data

46% Direct + 54% ResolvedMixing used in all calculations

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 10

Valid Simulation of Valid Simulation of p by HERWIGp by HERWIGValid Simulation of Valid Simulation of p by HERWIGp by HERWIG

Data well described by HERWIG

of Leading Jet Highest ET Jet

of Trailing Jet Cut 0.2 < YJB< 0.85

Applied to other plots

Direct

Direct + Resolved

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 11

Energy in the GapEnergy in the GapEnergy in the GapEnergy in the Gap

•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)•Agreement can be improved by tuning input parameters

PYTHIA HERWIG

2.6% Color Singlet 4.8% Color Singlet

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 12

Inclusive and Gap Cross SectionsInclusive and Gap Cross SectionsInclusive and Gap Cross SectionsInclusive and Gap Cross Sections

ETGap < 1.0 GeV

Addition of 4.8% color singlet MC improves agreement with data

Error bars show statistical errors only

dd

ddf Gap

/

/)(

Ratio of above plots

Inclusive

Gap Fraction:

Compare p Data to HERWIG

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 13

Gap Fractions for Different Gap EGap Fractions for Different Gap ETTGap Fractions for Different Gap EGap Fractions for Different Gap ETT

•Observed excess of Data over MC without CS exchange

•Data has better agreement with MC (95.2%) + CS (4.8%)

•Evidence that CS exchange is occurring

ETGap < 1.5 GeV ET

Gap < 2.0 GeV

ETGap < 0.5 GeV ET

Gap < 1.0 GeV

dd

ddf Gap

/

/)(

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 14

Tevatron and H1 ResultsTevatron and H1 ResultsTevatron and H1 ResultsTevatron and H1 Results

•Fraction of CSE at Tevatron• √s = 1800 GeV

• CDF: 1.13% ± 0.12(stat) ± 0.11(sys)

• D0: Rising Slightly

• Consistent within errors

• √s = 630 GeV

• CDF: 2.4% ± 0.7 ± 0.6

• ZEUS: 4.8% at √s = 300 GeV

•Gap Fraction at H1• Consistent with ZEUS within errors

• 6.6 pb-1 of Lumi

CDF & D0 CSE Fractions

•H1

Interjet Energy Flow at ZEUS . Patrick Ryan. Univ. of Wisconsin DPF , Aug. 27, 2004 - 15

SummarySummarySummarySummary

• Conclusions on p with Rapidity Gap• HERWIG + BFKL and PYTHIA + High-t describe data• Evidence for Color Singlet Exchange

• 3-5% of CSE added to data improves match at high • ZEUS results consistent with H1 within errors• ZEUS observes larger CSE than CDF/DO at lower √s

• CDF/D0: 1%/2.4% CSE at 1800/630 GeV

• Next steps• Include 98-2000 Data

• 3x higher statistics• Can go to higher jet ET Less sensitivity to underlying

event models• Study properties of color singlet exchange