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Tom Danielson University of Wisconsin Tim Gosau Hamburg University

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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Tom Danielson University of Wisconsin Tim Gosau Hamburg University

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  1. A Search for BFKL in DIS Multijets Tom Danielson University of Wisconsin Tim Gosau Hamburg University

  2. 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)

  3. 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

  4. 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)

  5. 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

  6. 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

  7. 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

  8. 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

  9. Dijet Event Dijet selected by these cuts. Looking for forward jets

  10. 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)

  11. 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

  12. 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

  13. 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

  14. 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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