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H  gg analysis at ATLAS

H  gg analysis at ATLAS. M. Escalier , B. Laforge. LPNHE Paris CNRS/IN2P3-Universités Paris 6&7. Status of TDR analysis Signal & background generation Kinematic variables Likelihood analysis Conclusion and outlooks. Special thanks to Arthur for let me use his laptop for some update.

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H  gg analysis at ATLAS

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  1. Hgg analysis at ATLAS M. Escalier, B. Laforge LPNHE Paris CNRS/IN2P3-Universités Paris 6&7 • Status of TDR analysis • Signal & background generation • Kinematic variables • Likelihood analysis • Conclusion and outlooks Special thanks to Arthur for let me use his laptop for some update Thanks L. Fayard, G. Unal (discussion, feedback)

  2. Status of TDR • Leading Order: CTEQ 2L • no K factor • Pythia 5.700 • ISR, FSR • Atlfast 2.0 from full reconstruction

  3. Signal/B S/√B=6.5, signal & background computed at LO

  4. Signal Hgg VBF • direct production gg fusion • associated production WH,ZH,ttH

  5. Signal pdf=CTEQ6L1 (comment of M. Spira) at Les Houches Using correction of HDecay for decay Hgg

  6. Irreductible background Background NLO calculation using Diphox 1.2, pdf=CTEQ6M • reductible background (LO Pythia), pdf=CTEQ6L1 g jet, 1 jet misidentified jet jet, 2 jets misidentified

  7. Higgs mass resolution With Pythia/ATLFAST s=1.34 GeV Next slides: use of s of full simu TDR for window 1.4 s Mgg (GeV)

  8. Thanks J. Ph. Guillet for help with Diphox Diphox definitions

  9. Analysis Requirements • CTEQ 6L1 pdf (LO fit), CTEQ 6M pdf for diphox (NLO) • Pythia 6.210, Atlfast 2.53, Diphox 1.2 • Cuts: • photon candidates: pT1>40 GeV, pT2>25 GeV • |h|<2.4 • transition crack of |h|=1.45, Dh=0.15 considered • Photon efficiency: 80% (Cf. M. Wielers) • Jet rejection factor: 2900 (Cf. M. Wielers) • photon Isolation cone R=0.4 ET<15 GeV In discussion (F. Derue: 1200-1600) cf. Athens 4th Atlas Worshop

  10. Branching ratio: depends on b mass and on QCD corrections 8.5% 56% Branching ratio: Pythia: running aQED for pythia (I mean by default) HDecay: QCD corrections more relevant No corrections aQED (better because real photons q2=0) • gg fusion :compatible with papers • R.Harlander and W.Kilgore   Phys Rev Lett 88,201801,2002 • C.Anastasiou and K.Melnikov Nucl Phys B646,220,2002 • K factor 1.7-2.5 depending on higgs mass • Ravindran, Smith, Van Neerven • KNLO=1.76 • VBF:compatible with talk of C. Oleari Total production cross-section What is the NLO Prediction ? HiGlu package (M. Spira et. al) gg fusion K=1.8 (using CTEQ6) VBF K=1.04 (using CTEQ6)

  11. Problem of resummation: C. Balazs has done resummation, use/compare his soft. later Ptgg • Ptgg<30 GeV • Ptgg>30 GeV likelihood analysis

  12. Ptgg distribution fsignal fbackground

  13. Cos q* fsignal fbackground

  14. Likelihood ratio R Search for optimal cut

  15. Results 8.8 6 % 8.25

  16. Conclusion • Background: • Irreductible background: • Use of NLO irreductible background • Need resummation • (but box is LO in Diphox) • use Dixon calculations (L. Fayard, G. Unal) • Does NNLO computation is possible ? • reductible background: • Know better the rejection factor (g jet) • Then look for NLO computation of g jet, jet jet

  17. Signal: • gg fusion and VBF comp. at NLO (but K=f(Pt)need MC at NLO) • gg fusion: Ravindran, Smith, Van Neerven • KNLO is not smal (1.76), KNNLO=1.16 (use of KNNLO in the future) • NNLO of VBF ? • likelihood analysis:gain not so much important • use neural network ? • Understand background of gg jet jet with 2 tagged jets • jet veto in central region

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