A Search for BFKL in DIS Multijets
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A Search for BFKL in DIS Multijets. Tom Danielson University of Wisconsin Tim Gosau Hamburg University. QCD Evolution. Control x and Q 2 dependence of parton distributions according to QCD Splitting functions give probability quark or gluon will split into parton pair

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A Search for BFKL in DIS Multijets

Tom Danielson

University of Wisconsin

Tim Gosau

Hamburg University


Qcd evolution
QCD Evolution

  • Control x and Q2 dependence of parton distributions according to QCD

    • Splitting functions give probability quark or gluon will split into parton pair

  • Test applicability of DGLAP evolution vs. BFKL

    • DGLAP should not be applicable at low xBj

      • Summed in terms of ln(Q2)

      • Terms involving ln(1/xBj) ignored

    • BFKL should be applicable at low xBj

      • Sums evolutions in terms of ln(1/xBj)


Parton energy and k t ordering

DGLAP: ordering in both kT and x

BFKL: not ordered in kT but ordered in x

Potential differences

DGLAP: Jets strongly correlated in Energy, azimuthal and polar angles

BFKL: Jets not necessarily strongly correlated

Expect more energetic jets in forward region with BFKL than with DGLAP

Parton Energy and kT Ordering


H1 inclusive dijet events
H1 Inclusive Dijet Events

  • f correlation of two most energetic jets in multijet events

    • 1996-1997 H1 data: ET > 7 GeV

    • Compare to DGLAP for NLO O(as2) (dijet) and NLO O(as3) (trijet)

      • O(as2): Data not described

      • O(as3): Agreement at high xBjStill excess at low Q2 and xBj

    • Excess events with small fseparation of highest ET jets

NLO: O(as3)

DESY–03–160 October 2003

NLO: O(as2)


Zeus multijet measurements
ZEUS Multijet Measurements

  • ZEUS inclusive dijet and trijet measurements well understood and modeled

    • Multijet cross sections vs. NLO calculations (L. Li and N. Krumnack)

    • DGLAP NLO dijet and trijet calculations describe data well in general

    • Examine if agreement extends to “BFKL” kinematic regions

Dijet

Trijet


Nlo vs zeus inclusive jets
NLO vs. ZEUS Inclusive Jets

  • Inclusive jet cross section vs. DISENT (S. Lammers and J. Terron)

  • Low xBjdisagreement between data and DISENT

  • Disagreement evident when jet required

    • Structure Function analyses do not require jets

    • Further explore this region requiring more than one jet


Strategy for studying bfkl
Strategy for Studying BFKL

  • Examine jet azimuthal and energy correlations using low xBj and low Q2

    • xBj < 10-2

    • Q2 < 150 GeV2

  • Jets not strongly correlated in energy and azimuthal angle indicate BFKL effects

    • DGLAP: Jets strongly correlated in ET, angles

      • “Back to back” in f

      • Correlation in h reflects ktcompensation

    • BFKL: Jets not strongly correlated

      • More energetic jets expected in forward region


Data and offline cuts
Data and offline cuts

  • Data: 1998-2000 electron and positron: 82.2 pb-1

  • DIS Kinematic Cuts

    • 10 < Q2 < 5000 GeV2 yjb > 0.04 yel < 0.6

    • cos(gh) < 0.7 hmax > 2.5 40 < E – pz < 60 GeV

    • (E – pz)elec < 54 GeV |z vertex| < 50 cm

  • Standard Dijet Cuts

    • ET,Breit > 5 GeV

    • -1 < hLab < 2.5

    • mjj > 25 GeV

  • Trigger Selection

    • DIS03 or HPP14

      • DIS03: Ee > 4GeV, re > 36cm

      • HPP14: 2 jets in lab frame minimum, ET > 2 (2.5) GeV

  • Cuts to isolate BFKL kinematics (not yet implemented)

    • Q2 < 150 GeV2

    • 10-4 < x < 10-2

    • DIS01

      • DIS01: Ee > 4GeV, 24 x 12 cm2 box cut

      • Prescaled


Dijet event
Dijet Event

Dijet selected by these cuts. Looking for forward jets


Lo monte carlo
LO Monte Carlo

  • ARIADNE v4.08

    • Color Dipole Model (CDM)

      • Gluons emitted from color field between quark-antiquark pairs

      • Supplemented with BGF processes

      • Gluons not necessarily kt ordered (BFKL-like)

  • LEPTO v6.5.1

    • Matrix Element Parton Shower (MEPS)

      • Parton cascade

      • Decreasing virtuality as cascade progresses

      • Radiated gluons kt-ordered (DGLAP-based)


Dijet data vs lepto
Dijet Data vs. LEPTO

  • ET in Breit Frame of 2 highest ET jets

  • Ordered in ET

  • Ordered in h

  • Reasonable agreement overall

Et2Bre

Et1Bre

h2Lab

h1Lab


Dijet data vs ariadne
Dijet Data vs. ARIADNE

  • ET in Breit Frame of 2 highest ET jets

  • Ordered in ET

  • Ordered in h

  • Need to investigate discrepancies with ARIADNE

Et2Bre

Et1Bre

h2Lab

h1Lab


Comparison of analyses
Comparison of Analyses

  • Initial comparison of T.D. and T. Gosau

    • ET in Breit Frame of 2 highest ET jets

    • Ordered in ET

    • Working on this

Et1Bre

Et2Bre


Summary
Summary

  • Comparison beginning between 2 analyses

  • Reasonable agreement between ZEUS 98-00 data and LEPTO

  • Disagreement between ZEUS 98-00 data and ARIADNE needs investigation

  • Plans

  • Repeat H1 measurement

    • Higher ZEUS 98-00 luminosity an advantage

      • H1 luminosity 21 pb-1 from 96/97

      • ZEUS 98-00: 82.2 pb-1

  • Find kinematics and variables that enhance discrepancies between BFKL and DGLAP.


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