1. AA->HH Study -Current status of AA->4b BG- Shin-ichi Kawada (AdSM, Hiroshima University) 19th General Meeting @ KEK (2011/1/29)1 AA->HH subgroup : Experiment

2. Outline Introduction Previous results Current issues --- Calculation of AA->4b BG Results – Cross-section of AA->4b BG – Histograms Summary & Next plan 19th General Meeting @ KEK (2011/1/29)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. 19th General Meeting @ KEK (2011/1/29)3

4. About PLC 19th General Meeting @ KEK (2011/1/29) 4 Electrons Backward Compton scattering Gamma-gamma collision ILC : e+ e- collision PLC : 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. 19th General Meeting @ KEK (2011/1/29)5 4b = b b-bar b b-bar

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. 19th General Meeting @ KEK (2011/1/29)6 BGusualcheat AA->WW2.695.85 AA->ZZ1.615.85

7. Previous results (2) Other background (AA->4b) – Calculate the cross-section of AA->4b with using GRACE and BASES. – Total cross-section = 960fb (√s = 270GeV, no cuts) – Making histograms cos_theta, invariant mass, energy, etc… 19th General Meeting @ KEK (2011/1/29)7

8. Calculation of the cross-section of AA->4b Tried to calculate the cross-section with several conditions as below. – √s = 270GeV with cuts cos_theta of quarks, 2-jet invariant mass – convolute luminosity distribution – convolute luminosity distribution with cuts 19th General Meeting @ KEK (2011/1/29)8

9. Cut criteria 19th General Meeting @ KEK (2011/1/29)9 γ γ b b-bar b g* B A Both invariant mass of A (M A ) and that of B (M B ) would be small. If (M A < M cut ) and (M B < M cut ), then cut that events. M cut : Cut value for 2-jet invariant mass (GeV) Main reaction of AA->4b

10. Cut results 19th General Meeting @ KEK (2011/1/29)10 |cos_theta| cutM cut cut√s = 270GeV (fb)with lumi. (fb) None 960109 None20GeV77877.1 None40GeV40427.8 <=0.99None10234.6 <=0.9920GeV10024.7 <=0.9940GeV80.18.57 <=0.8040GeV4.110.577 cf : Total cross-section of signal : 0.19fb Effective cross-section of signal : 0.013fb σ signal < σ BG !!!

11. Discussion --- Cut results Try to more cuts – Now using : cos_theta of quarks, 2-jet invariant mass Can we use other physical values as the cut parameters? – Energy of 2-jet Energy of 2-jet of 4b BG is near to the energy of initial photon beam. – Cos_theta of lowest 2-jet invariant mass – And more…? 19th General Meeting @ KEK (2011/1/29)11

12. Histograms Making 2-D and 3-D histograms between signal and 4b BG – 2-D : 2-jet invariant mass (lowest & that’s pair) – 3-D : 2-jet invariant mass & cos_theta of lowest 2- jet invariant mass 19th General Meeting @ KEK (2011/1/29)12 LowINV2-jet inv. mass of pair of LowINV LowINV 2-jet inv. mass of pair of LowINV cos_theta of LowINV LowINV = lowest 2-jet inv. mass 2-D 3-D

13. Results (2-D) 19th General Meeting @ KEK (2011/1/29)13 Signal 4b BG (√s = 270GeV) 4b BG (with luminosity) LowINV 2-jet inv. mass of pair of LowINV

14. Results (3-D) 19th General Meeting @ KEK (2011/1/29)14 Signal 4b BG (with luminosity) LowINV 2-jet inv. mass of pair of LowINV cos_theta of LowINV 4b BG (√s = 270GeV)

15. Discussion --- Histograms Event distribution is different between signal and 4b BG. – 2-jet invariant mass Signal : peak @ ~120GeV 4b BG : peak @ <50GeV – Cos_theta of lowest 2-jet invariant mass Signal : flat 4b BG : peak @ |cos_theta|~1 These parameters could be used as the cut parameter. 19th General Meeting @ KEK (2011/1/29)15

16. Summary Calculation of AA->4b BG cross-section – 960fb (√s = 270GeV) – 109fb (with luminosity) – Applied some cuts, but σ signal < σ BG !!! – Other physical values could be used as the cut parameter. Making histograms of 2-jet invariant mass and cos_theta – Event distribution is different between signal and 4b BG. 19th General Meeting @ KEK (2011/1/29)16

17. Next plan Try to calculate AA->4b cross-section with other cuts. – Now running… Creating AA->4b event generator – Now creating with SPRING. 19th General Meeting @ KEK (2011/1/29)17

18. Backup slide

19. Luminosity distribution