AA->HH Study -Current status of AA->4b BG- - PowerPoint PPT Presentation

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

  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)

  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)

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

  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 19th General Meeting @ KEK (2011/1/29)

  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. 19th General Meeting @ KEK (2011/1/29)

  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)

  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)

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

  10. Cut results cf : Total cross-section of signal : 0.19fb Effective cross-section of signal : 0.013fb σsignal < σBG!!! 19th General Meeting @ KEK (2011/1/29)

  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)

  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 3-D LowINV = lowest 2-jet inv. mass 2-D cos_theta of LowINV 2-jet inv. mass of pair of LowINV 2-jet inv. mass of pair of LowINV LowINV LowINV 19th General Meeting @ KEK (2011/1/29)

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

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

  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)

  16. Summary • Calculation of AA->4b BG cross-section • 960fb (√s = 270GeV) • 109fb (with luminosity) • Applied some cuts, but σsignal < σBG!!! • 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)

  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)

  18. Backup slide

  19. Luminosity distribution