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