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QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 1 Results from ZEUS and H1 Tom Danielson University of Wisconsin.

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Presentation on theme: "QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 1 Results from ZEUS and H1 Tom Danielson University of Wisconsin."— Presentation transcript:

1 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 1 Results from ZEUS and H1 Tom Danielson University of Wisconsin – Madison on behalf of the ZEUS and H1 collaborations Dijet and Trijet Correlations Inclusive Forward Jet Production Rencontres de Moriond: March 22 2007, Italy QCD Dynamics at Low-x Bj in ep Collisions at HERA

2 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 2 Testing Parton Evolution: Jets at low x Bj Moving to LHC: Are extracted PDFs usable in the LHC kinematic range (1 > x > 10 -6 ) ? Does DGLAP evolution work sufficiently to extrapolate? Study QCD evolution schemes with jets at low x Bj at HERA Jets found with k T algorithm in inclusive mode DGLAP: sums over ln(Q 2 ) terms (LEPTO, RAPGAP, DISENT, NLOjet++) ordering in both k T and x well tested over large range of Q 2 BFKL: sums over ln(1/x) terms (~ ARIADNE (CDM)) Strong ordering in x, but not ordered in k T More energetic forward jets Jets less correlated in energies, angles CCFM: k T factorization (CASCADE) Evolution in Q 2, x Approaches BFKL for low x Bj, DGLAP for high Q 2 angular ordering (instead of k T ordering) uses unintegrated parton densities First examine DGLAP NLO calculations

3 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 3 H1 Dijet Azimuthal Correl. vs. x Bj Examine   correlation of dijets at low x Bj   Sensitive to parton evolution scheme, gluon radiation Jets are back-to-back without gluon emission Test DGLAP calculations from NLOjet Normalize to visible cross section for   < 170 in each bin of x Bj Cancellation of renormalization scale uncertainties Disagreement between data, NLOjet calculations at low x Bj, low   Kinematic region where DGLAP needs checking

4 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 4 ZEUS Dijet p T Correlations vs. x Bj |  p T | sensitive to parton evolution, gluon radiation |  p T | = 0 without gluon radiation NLOjet (DGLAP) calculations at O(  s 2 ) do not describe dijet data at low x Bj NLOjet calculations at O(  s 3 ) describe data, even at low x Bj Higher order terms important at low x Bj Allows for more gluon emission

5 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 5 ZEUS Trijet p T Correlations vs. x Bj Expand study of |  p T | by examining trijets Higher order measurement (O(  s 2 ) at LO) NLOjet calculations at O(  s 3 ) describe the data Better description at higher values of x Bj Higher-order NLO calculations not available Effect much less pronounced than for dijets vs. O(  s 2 ) NLOjet calculations

6 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 6 ZEUS 2,3-jet Azimuthal Correl. vs. Q 2, x Bj   < 120° → high-E T forward jet Measurements sensitive both to angular correlations, forward jets NLOjet calculations at O(  s 3 ) describe dijet, trijet data, even at low x Bj Dijets at low x Bj : O(  s 3 ) calcs for dijets ~ 10 x O(  s 2 ) calcs For phase space tested, DGLAP works when higher-order terms included DijetsDijetsTrijetsTrijets

7 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 7 ZEUS Inclusive Forward Jets: NLO Calculations Select forward jets with 2 0.036 DISENT NLO predictions in agreement with data within theoretical uncertainties Theoretical uncertainty increases at lower Q 2, x Bj Higher-order terms important ZEUS inclusive forward jets described by DISENT NLO DGLAP calcs.

8 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 8 H1 Trijet Correlations Parton evolution for multijet events examined: Angular correlations Normalized jet energies For Inclusive trijet Trijet with 1, 2 forward jets Inclusive trijet data generally well-described by NLOjet calculations at O(  s 3 ) Data above calculations at low x Bj Inclusive trijet data generally well-described by NLOjet calculations at O(  s 3 ) Data above calculations at low x Bj Inclusive Trijets

9 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 9 H1 Forward Trijet Measurements Select forward jets with x jet > 0.035,  jet < 20° 2 forward jets: disagreement with NLOjet at low x Bj for d  / dx Bj More gluons expected with 2 forward jets More sensitive to higher- order terms Jets selected to favor more gluon emission NLOjet describes angular correlations well within theorectical uncertainties 1 forward jet 2 forward jets

10 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 10 Leading-Order Models: Dijet Azim. Correl, Incl. Forward Jets ZEUS inclusive forward jets: Expect more forward jets with BFKL, CCFM at low x Bj LEPTO (DGLAP) consistently below measurements CASCDE (CCFM) inconsistent in description of data Better description from J2003 set 2 than set 1 ARIADNE (CDM, ~BFKL) gives best overall description H1 dijet azimuthal correlations: Expect broader   spectrum from BFKL, CCFM CASCADE with J2003 pdf set describes data at higher x Bj CASCADE predictions dependent on unintegrated gluon PDF All models fail to describe   at low x Bj

11 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 11 Leading-Order Models: H1 Inclusive Trijet Correlations Trijet sample Scaled jet energies better described by CDM (~BFKL) than RAPGAP (DGLAP) Both CDM and RAPGAP (DGLAP + res. photon) fail to describe both angular correlations Four-jet sample CDM provides better description overall No NLO calculations available

12 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 12 Summary: Low-x Bj Dynamics at HERA DGLAP NLO calculations describe data in general Higher-order terms important at low Q 2, x Bj NLO calculations do not describe Dijet azimuthal correlations, when normalized to visible cross section Trijet cross sections for trijets with 2 forward jets at very small x Bj Leading-order models describe data inconsistently DGLAP-based models consistently fail to describe inclusive forward jet measurements, dijet and trijet correlations CASCADE (CCFM) dependent on unintegrated PDF. Fails to describe inclusive forward jet cross sections CDM (~BFKL) gives best overall description, but fails to describe dijet azimuthal correlations, trijet angular correlations LHC implications: LHC low-x limit: ~10 -6 Tevatron low-x limit: ~10 -3 HERA analyses have tested QCD evolution to x Bj ~ 10 -4

13 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 13 Backup Slides

14 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 14 Kinematic Coverage of Colliders Tevatron LHC HERA

15 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 15 H1 Dijet Azimuthal Correl. vs. x Bj Without normalization to visible cross section Reasonable description of dijet data from NLO 3-jet calculation Large theoretical uncertainties

16 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 16 H1 Dijet Azimuthal Correlations: Complete LO Results CASCADE with J2003 pdf set describes data at higher x Bj CDM, RAPGAP (dir and res) fail to describe low-  regions CDM has slightly better description at low x Bj CASCADE (CCFM) LEPTO (CDM) → used with ARIADNE RAPGAP dir (DGLAP) RAPGAP res (+ resolved photon) LEPTO (CDM) → used with ARIADNE RAPGAP dir (DGLAP) RAPGAP res (+ resolved photon)

17 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 17 ZEUS Forward Jets: Complete Results

18 QCD Dynamics in low-x DIS T. Danielson, U. WisconsinRencontres de Moriond, March 22, 2007 - 18 ZEUS Dijet and Trijet p T Correlations vs. x Bj

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