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AA->HH Study Event generation & Analysis of AA->4b BG

AA->HH Study Event generation & Analysis of AA->4b BG. Shin-ichi Kawada (AdSM, Hiroshima University). Outline. Introduction Previous results Today’s topic --- AA->4b BG Event generation Analysis Summary & Next plan. Introduction.

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AA->HH Study Event generation & Analysis of AA->4b BG

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  1. AA->HH StudyEvent generation & Analysis ofAA->4b BG Shin-ichi Kawada (AdSM, Hiroshima University) 21st General Meeting @ KEK (2011/7/16)

  2. Outline • Introduction • Previous results • Today’s topic --- AA->4b BG • Event generation • Analysis • Summary & Next plan 21st General Meeting @ KEK (2011/7/16)

  3. Introduction • Photon Linear Collider (PLC) has been proposed as one of the options of ILC. • It is expected that we can observe the Higgs self-coupling in PLC. • Feasibility study of Higgs pair creation in PLC is needed. 21st General Meeting @ KEK (2011/7/16)

  4. About PLC ILC : e+ e- collision PLC : gamma gamma collision Electrons Backward Compton scattering gamma-gamma collision 21st General Meeting @ KEK (2011/7/16)

  5. Reaction in gamma-gamma collision • Signal : AA->HH->4b • Many backgrounds • AA->WW, ZZ, 4b, etc… • Analysis of background reduction is necessary. • We assumed that Higgs mass equals to 120GeV in this study. 4b = b b-bar b b-bar 21st General Meeting @ KEK (2011/7/16)

  6. Previous results (1) • Main backgrounds • AA->WW (~11.6pb, 1.5*107 events/year) • AA->ZZ (~9.42fb, 1.2*104 events/year) • Analysis with Neural Network • We can observe Higgs pair creation if we can develop good b-tagging method and jet clustering. 21st General Meeting @ KEK (2011/7/16)

  7. Previous results (2) • Other background --- AA->4b • cross-section = 109fb (with luminosity) • ~ 1.4*105 events/year • need the detector simulation & analysis 21st General Meeting @ KEK (2011/7/16)

  8. Topic (1) : Event generation of AA->4b • Event generator : GRACE, BASES, SPRING • Cut at the BASES level • (2-jet invariant mass) < 15 GeV were cut • cross-section = 46.6fb • ~6*104 events/year • Detector simulation : JSFReadParton • Two types of AA->4b events were generated • optimistic 4b • pessimistic 4b 21st General Meeting @ KEK (2011/7/16)

  9. Event type of AA->4b optimistic event pessimistic event γ b γ b b-bar b-bar b b γ b-bar γ b-bar : color string 21st General Meeting @ KEK (2011/7/16)

  10. Topic (2) : Analysis of AA->4b reduction table m1, m2 : reconstructed particle mass σ2j : resolution evis : visible energy Pl : longitudinal momentum |csjmax| : largest |cosθ| of jet input these data to neural network (NN) 21st General Meeting @ KEK (2011/7/16)

  11. Input parameters signal 4b_pes χH2 χZ2 χA2 transverse momentum longitudinal momentum 21st General Meeting @ KEK (2011/7/16)

  12. Input parameters signal 4b_pes # of b-flavor jet (nsig=3.5, noffv=2) # of tracks # of b-flavor jet (nsig=3.5, noffv=1) visible energy ycut value of jet clustering 21st General Meeting @ KEK (2011/7/16)

  13. Input parameters signal 4b_pes thrust sphericity aplanarity Y-value 21st General Meeting @ KEK (2011/7/16)

  14. Result not bad, but not enough 21st General Meeting @ KEK (2011/7/16)

  15. Discussion • Use other useful parameter • cosθof jet (cosθof 2-jet) • event shape • more tight cuts & input to NN • Jet pairing • choose the pair of least χH2, then get the variables • choose the pair of least χA2, then get the variables • compare these variables, and try to cut them or input to NN. 21st General Meeting @ KEK (2011/7/16)

  16. Summary & Next plan • Event generation with SPRING & detector simulation of AA->4b BG has been finished. • Reduction of AA->4b BG is not bad, but not enough. • Other parameter (cosθ of jet, event shape) would be useful.  I will check. • Compare variables which the pair of least χH2 and pair of least χA2 , and try to cut / input to NN. 21st General Meeting @ KEK (2011/7/16)

  17. Backup slides 21st General Meeting @ KEK (2011/7/16)

  18. pre-selection • Lorentz factor of 2-jet β2j > 0.05 • |cosθ2j| < 0.99 • θ : angle between beam axis and 2-jet • nbj >= 3 • nbj : # of b-flavor jets with nsig = 3.0 & noffv = 1 • nbtj>= 2 • nbtj : # of b-flavor jets with nsig = 3.0 & noffv = 2 21st General Meeting @ KEK (2011/7/16)

  19. significance # of generated HH = 5*104 # of generated 4b = 1*106 80 : 5year*16events/year (signal generation) 3*105 : 5year*6*104events/year (4b BG generation) 21st General Meeting @ KEK (2011/7/16)

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