interjet energy flow. patrick ryan, univ. of wisconsin collaboration meeting, june 6, 2005 - 1...
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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