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BFKL Dynamics at the Tevatron

Experimental Tests of the BFKL Mechanism Zarah Casilum State University of New York at Stony Brook for the D0 Collaboration 1997 Joint April APS/AAPT Meeting April 18-21, 1997 Washington, DC. x 1 , k T1. x 2 , k T2. x n , k Tn. BFKL Dynamics at the Tevatron.

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BFKL Dynamics at the Tevatron

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  1. Experimental Tests of the BFKL MechanismZarah CasilumState University of New York at Stony Brookfor the D0 Collaboration1997 Joint April APS/AAPT MeetingApril 18-21, 1997Washington, DC

  2. x1, kT1 x2, kT2 xn, kTn BFKL Dynamics at the Tevatron • Inclusive dijet production at large rapidities • Semi-hard region: For large x: • The BFKL formalism resums (asDh) to all orders in as (only leading logs) into the partonic cross section by using a multigluon amplitude

  3. The BFKL resummation results in an exponential growth of the partonic cross section • Contribution of real gluons leads to additional radiation between the two jets Decorrelation of the dijets in the azimuth Dijet decorrelation at large rapidities • Tevatron at a fixed cms energy (1.8 TeV) -At large Dh, PDF’s control dijet cross section -Difficult to see the growth of cross section with Dh -Look for evidence of additional radiation as Dh increases

  4. pt1f1 h1 Higher Order pt1f1 h1 LO pt2f2 h2 pt2f2 h2 • Measuring azimuthal decorrelation (cartoon analogy) Qualitative:broadening 1/N dN/dDf as Dh Quantitative:falling off <cos(p-Df)> as Dh

  5. The DO Detector • Hermetic coverage over large rapidity (|h| < 4.0) • Fine transverse segmentation (0.1 x 0.1 in Dh x Df) • Good jet energy response and resolution Side view of the DO Detector

  6. h=-3.5 h=3.5 Tagging Jet1 J1 X(Ji) Df Tagging Jet2 J2 Dh Event topology and Analysis variables • Jets: ET sums in 0.7 cone in h x f space • Single jet triggers: Inclusive: ET>12 Gev Forward: ET>12 GeV and |h|>1.6 • Multiple pp interactions and fake jets removed • Offline defines jets with ET>20 GeV , and |h|<3.5 • Rapidity ordering and tagging jets at extreme rapidities: (h1,f1),(h2,f2) • Require rapidity boost • Analysis variables: Dh = h1 - h2 and Df = f1 - f2

  7. Data Results: 1/N dN/dDf vs. Dh <cos(p-Df)> vs. Dh LLA

  8. 1800/630 GeV Dijet Cross Section Ratio at large Dh • Mueller and Navelet suggested a method to explore BFKL dynamics by describing s dependence(Nucl. Phys. B282 (1987) 727) • Fix x1, x2, Q2 and take the ratio of the cross sections at two different center of mass energies, sA and sB • Cancellation of the parton distribution functions, hence removing large source of theoretical error • By measuring R(1800,630) at the Tevatron, we can probe the perturbative BFKL dynamics and extract the effective coupling of the BFKL pomeron, aBFKL=1+12asln2/p (using as(Q2)=0.16)

  9. Q2 and x • Data set • 1800 GeV: integrated Lum = 1.5 nb-1 • 630 GeV: integrated Lum = 34 nb-1 • Offline cuts: similar cuts as the decorrelation analysis, except that |h|>2.0 • Q2 and x values: 1 bin: 400-1000GeV2 several bins: 0.06-0.25 630 GeV 1800 GeV

  10. Summary and Outlook • Decorrelation study -Qualitatively, data show trends consistent with BFKL -However, quantitative results do not agree with LLA BFKL but agree well with Herwig(V5.8, parton shower model, including ISR,FSR, interference terms) -LLA BFKL with improved kinematics will be available soon and NLL BFKL calculations are in progress • Dijet cross section ratio study -study under way -Very promising measurement;directly sensitive to BFKL dynamics

  11. Q2 Distribution 630 GeV 1800 GeV

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