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

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

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)3

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

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)5

6. Previous results (1) Main backgrounds – AA->WW (~11.6pb, 1.5*10 7 events/year) – AA->ZZ (~9.42fb, 1.2*10 4 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)6 BGusualcheat AA->WW2.695.85 AA->ZZ1.615.85

7. Previous results (2) Other background --- AA->4b – cross-section = 109fb (with luminosity) – ~ 1.4*10 5 events/year – need the detector simulation & analysis 21st General Meeting @ KEK (2011/7/16)7

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*10 4 events/year Detector simulation : JSFReadParton Two types of AA->4b events were generated – optimistic 4b – pessimistic 4b 21st General Meeting @ KEK (2011/7/16)8

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

10. Topic (2) : Analysis of AA->4b 21st General Meeting @ KEK (2011/7/16)10 reduction table HH4b_opt4b_pes generate500001000000 pre-selection29958240750205963 χ H 2 < 1502972390527131711 χ A 2 > 100288403950583505 190 < evis < 320273292185143974 |Pl| < 70272222114142130 |csjmax| < 0.9523979990817276 sphericity > 0.123516747513559 m 1, m 2 : reconstructed particle mass σ 2j : resolution evis : visible energy Pl : longitudinal momentum |csjmax| : largest |cosθ| of jet input these data to neural network (NN)

11. Input parameters 21st General Meeting @ KEK (2011/7/16)11 χH2χH2 χA2χA2 χZ2χZ2 longitudinal momentum transverse momentum signal 4b_pes

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

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

14. Result 21st General Meeting @ KEK (2011/7/16)14 remained HHremained 4bsignificance optimistic91551701.81 pessimistic5590931.47 not bad, but not enough

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

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 χ H 2 and pair of least χ A 2, and try to cut / input to NN. 21st General Meeting @ KEK (2011/7/16)16

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

18. pre-selection Lorentz factor of 2-jet β 2j > 0.05 |cosθ 2j | < 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)18

19. significance 21st General Meeting @ KEK (2011/7/16)19 # of generated HH = 5*10 4 # of generated 4b = 1*10 6 80 : 5year*16events/year (signal generation) 3*10 5 : 5year*6*10 4 events/year (4b BG generation)