1. AA->HH Study AA->4b analysis & (preliminary) Summary Shin-ichi Kawada (AdSM, Hiroshima University) 22nd General Meeting @ KEK (2011/9/3)1

2. Outline Introduction Previous results Today’s topic – AA->4b BG analysis – analysis of BG suppression (AA->WW, ZZ, 4b) Summary & Next plan 22nd General Meeting @ KEK (2011/9/3)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. 22nd General Meeting @ KEK (2011/9/3)3

4. About PLC 22nd General Meeting @ KEK (2011/9/3)4 Electrons Backward Compton scattering ILC : e+ e- collision PLC : gamma-gamma collision gamma-gamma collision

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. 22nd General Meeting @ KEK (2011/9/3)5 4b = b b-bar b b-bar

6. Previous result (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. 22nd General Meeting @ KEK (2011/9/3)6 BGusualcheat AA->WW2.695.85 AA->ZZ1.615.85

7. Previous result (2) Other background --- AA->4b – cross-section = 46.6fb (with luminosity & (2-jet invariant mass) < 15 GeV were cut) – ~ 6*10 4 events/year – need the detector simulation & analysis 22nd General Meeting @ KEK (2011/9/3)7 γ b b-bar optimistic event γ γ b b b-bar pessimistic event : color string γ b b-bar

8. Topic (1) : AA->4b BG analysis 22nd General Meeting @ KEK (2011/9/3)8 at the 21st General Meeting 4b(opt) : 1.81σ 4b(pes) : 1.47σ not bad, but not enough need more effective cuts/NN analysis use other useful other parameters cosθ of jet (cosθ of 2-jet) event shape (thrust, sphericity, Y-value, etc...) jet pairing jet pair of least χ H 2 -> χ H 2, cosθ of 2-jet jet pair of least χ A 2 -> χ A 2, cosθ of 2-jet

9. Analysis procedure (1) MC samples – remained events after W filter & Z filter 22nd General Meeting @ KEK (2011/9/3)9 real clustering signal4b(opt)4b(pes) generate500001000000 pre-selection29958241318287776 W filter771310831936 Z filter60426241240 cheat clustering signal (cheat) 4b(opt)4b(pes) generate500001000000 pre-selection29152241318287776 W filter (cheat) 2411545357422 Z filter (cheat) 2298730775743 input these events to NN

10. Analysis procedure (2) 17 Input parameters to NN – no relation to χ 2 (11 parameters) visible energy, # of tracks, ycut value of jet clustering, thrust, sphericity, Y-value, cosθ of jet (4), max|cosθ of jet| – jet pairing of least χ H 2 (3 parameters) χ H 2, cosθ of 2-jet (2) – jet pairing of least χ A 2 (3 parameters) χ A 2, cosθ of 2-jet (2) 22nd General Meeting @ KEK (2011/9/3)10

11. Result 22nd General Meeting @ KEK (2011/9/3)11 real clusteringsignal4b(opt) remained events402516 significance (evaluated signal & 4b BG only) 1.92σ real clusteringsignal4b(pes) remained events312824 1.43σ cheat clusteringsignal (cheat) 4b(opt) remained events2217316 5.59σ cheat clusteringsignal (cheat) 4b(pes) remained events2158717 5.49σ Good suppression!!

12. Discussion Significance (signal v.s. single BG) with cheat jet clustering is good! – signal (cheat) v.s. WW (cheat) : 5.85σ – signal (cheat) v.s. ZZ (cheat) : 5.85σ – signal (cheat) v.s. 4b (optimistic) : 5.59σ – signal (cheat) v.s. 4b (pessimistic) : 5.49σ try to apply the NN analyses to all events! 22nd General Meeting @ KEK (2011/9/3)12

13. Topic (2) : Analysis of BG suppression Analysis procedure 1.pre-selection 2.W filter (1st NN selection) 3.4b filter (2nd NN selection) 4.Z filter (3rd NN selection) Cross-section : WW > 4b > ZZ 22nd General Meeting @ KEK (2011/9/3)13

14. pre-selection Lorentz factor β 2j > 0.05 |cosθ of 2-jet| < 0.99 nbj >= 3 – # of b-flavor jets with nsig=3.0 & noffv=1 analysis nbtj >= 2 – # of b-flavor jets with nsig=3.0 & noffv=2 analysis 22nd General Meeting @ KEK (2011/9/3)14 to suppress huge WW BG

15. Input parameters to NN 1st NN selection --- 9 parameters – χ H 2, χ Z 2, # of b-flavor jet, etc... 2nd NN selection --- 17 parameters – same as page10 3rd NN selection --- 10 parameters – χ H 2, χ W 2, χ Z 2, etc... 22nd General Meeting @ KEK (2011/9/3)15 Details are shown in page24.

16. Cut Summary real clustering & 4b (optimistic) 22nd General Meeting @ KEK (2011/9/3)16 HHWWZZ4b(opt) expected events (# of MC events) 80 (50000) 73100000 (75000000) 59350 (1000000) 293600 (1000000) pre-selection47.93 (29958) 81655 (83777) 5167 (87057) 70851 (241318) W filter12.34 (7713) 8.772 (9) 193.4 (3259) 318.0 (1083) 4b (opt) filter7.262 (4539) 1.949 (2) 73.89 (1245) 7.340 (25) Z filter4.823 (3018) 0.9747 (1) 9.377 (158) 3.817 (13)

17. Cut Summary real clustering & 4b (pessimistic) 22nd General Meeting @ KEK (2011/9/3)17 HHWWZZ4b(pes) expected events (# of MC events) 80 (50000) 73100000 (75000000) 59350 (1000000) 293600 (1000000) pre-selection47.93 (29958) 81655 (83777) 5167 (87057) 84491 (287776) W filter12.34 (7713) 8.772 (9) 193.4 (3259) 568.4 (1936) 4b (pes) filter8.238 (5149) 0 (0) 84.40 (1422) 13.21 (45) Z filter4.994 (3121) 0 (0) 7.359 (124) 5.872 (20)

18. Cut Summary cheat clustering & 4b (optimistic) 22nd General Meeting @ KEK (2011/9/3)18 HH (cheat)WW (cheat)ZZ (cheat)4b(opt) expected events (# of MC events) 80 (50000) 73100000 (75000000) 59350 (1000000) 293600 (1000000) pre-selection46.64 (29152) 55836 (57287) 4172 (70292) 70851 (241318) W (cheat) filter38.58 (24115) 4.873 (5) 98.94 (1667) 1331 (4535) 4b (opt) filter35.56 (22223) 3.899 (4) 41.78 (704) 3.817 (13) Z (cheat) filter33.26 (20787) 1.949 (2) 5.045 (85) 3.817 (13)

19. Cut Summary cheat clustering & 4b (pessimistic) 22nd General Meeting @ KEK (2011/9/3)19 HH (cheat)WW (cheat)ZZ (cheat)4b(pes) expected events (# of MC events) 80 (50000) 73100000 (75000000) 59350 (1000000) 293600 (1000000) pre-selection46.64 (29152) 55836 (57287) 4172 (70292) 84491 (287776) W (cheat) filter38.58 (24115) 4.873 (5) 98.94 (1667) 2179 (7422) 4b (pes) filter34.50 (21562) 2.924 (3) 27.66 (466) 2.642 (9) Z (cheat) filter33.06 (20662) 2.924 (3) 5.935 (100) 2.642 (9)

20. (Preliminary) Summary We can observe the Higgs self-coupling with ~5σ if we use cheat jet clustering. It is possible to measure the Higgs self- coupling in PLC if we can develop good jet clustering algorithm. 22nd General Meeting @ KEK (2011/9/3)20

21. Next Plan Check the statistical fluctuation Check/Evaluate the NN systematic error – Now : (training file) = (test file) Write a paper 22nd General Meeting @ KEK (2011/9/3)21

22. Backup slides 22nd General Meeting @ KEK (2011/9/3)22

23. sphericity, Y-value 22nd General Meeting @ KEK (2011/9/3)23 normalized momentum tensor M ab p i : momentum of particle i 3*3 matrix eigenvalue

24. Input parameters to NN (details) 22nd General Meeting @ KEK (2011/9/3)24 1st --- 9 parameters χ H 2, χ Z 2, visible energy, # of tracks, ycut value of jet clustering, longitudinal momentum, transverse momentum, # of b-flavor jets with nsig = 3.5 & noffv = 1 analysis, # of b-flavor jets with nsig = 3.5 & noffv = 2 analysis 2nd --- 17 parameters 3rd --- 10 parameters same as page10 χ H 2, χ W 2, χ Z 2, energy of 2-jet (2), visible energy, # of tracks, longitudinal momentum # of b-flavor jets with nsig = 3.5 & noffv = 1 analysis, # of b-flavor jets with nsig = 3.5 & noffv = 2 analysis