Interjet energy flow in php
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Interjet Energy Flow in PHP. Patrick Ryan University of Wisconsin Claire Gwenlan Oxford University June 10, 2005. ZEUS Collaboration Meeting DESY. Use pQCD to study diffraction Hard Diffractive PHP Hard: High E T Jets (E T > 5 GeV) Diffractive: Gap between jets

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Interjet Energy Flow in PHP

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Interjet energy flow in php

Interjet Energy Flow in PHP

Patrick Ryan

University of Wisconsin

Claire Gwenlan

Oxford University

June 10, 2005

ZEUS Collaboration Meeting

DESY


Rapidity 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: Dh

ETGap = Total ET between leading and trailing jets

Gap Event: ETGap < ETCut

Gap indicates color singlet exchange

Rapidity Gap Events

q

t

2p

g Remnant

f

Leading

Jet

Dijet Events with large Rapidity separation and ETGap < ETCut

Gap

ET

Trailing

Jet

p Remnant

0

-2.4

h

2.4

All Dijet Events with large Rapidity separation


Simulation of g p events zeus amadeus

Simulation of gp EventsZEUS - 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 xg distributions to data

  • Color Singlet Exchange MC

    • HERWIG: BFKL

      • Uses BFKL Pomeron as exchange object in Rapidity Gap events

    • PYTHIA: High-t g

      • Purpose is simply to match the data

      • Note: Rapidity Gap not due to photon exchange


Event selection and x g obs 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

ET1,2 > 5.1, 4.25 GeV

|h1,2| < 2.4

½|h1 + h2| < 0.75

[(Spx)2 + (Spy)2] / SET < 2 GeV1/2

2.5 < |h1 - h2| < 4.0  Gap Definition

4 Gap Samples

ETCUT = 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

Event Selection and xgOBS Fitting

HERWIG xgOBSFit to Data

Direct + Resolved

Direct

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


Gap e t cross section default zeus pythia herwig

Gap ET Cross Section Default ZEUS PYTHIA & HERWIG

HERWIG

PYTHIA

  • 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


Large systematic differences default pythia herwig

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 ET bins

      • Region without CS contribution

    • Generate AMADEUS using tuned parameters


Pythia tuning

PYTHIA 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

pTMin 1: pT of Hardest interaction

pTMin2: pT of all secondary interactions


Herwig tuning

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

    • PTMIN1 = 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

    • PTMIN1 = 2.7 GeV


Kinematic variables herwig

Kinematic Variables - HERWIG

Default HERWIG

Tuned HERWIG

  • Tuned HERWIG gives better description of Data than default HERWIG


Kinematic variables pythia

Kinematic Variables – PYTHIA

Default PYTHIA

Tuned PYTHIA

  • Tuned PYTHIA gives comparable description of Data

    • Now have two MCs that describe data well


Gap e t cross section tuned pythia and herwig

Gap ET Cross SectionTuned 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


Gap fraction

Gap Fraction

Inclusive Cross Section (s Inc )

Gap Cross Section (sGap)

ETGap < 1.0 GeV

Gap Fraction = sGap / sInc

MC + CS gives good description of data


Old vs new results

Old vs. New Results

Preliminary ICHEP 2002

New Results (P.R. and C.G.)

  • New Results: Better description of data at large Dh

    • Improves confidence in CS extraction


Comparison between p r c g

Comparison Between P.R & C.G

Gap ET

Delta Eta

Data unfolded with PYTHIA without CS

Excellent agreement between analyses


Interjet energy flow summary

Interjet 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 & Dh 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


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