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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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