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Particle Physics 735 Spring 2007

A study on. Particle Physics 735 Spring 2007. Higgs Production. Gluon-gluon fusion highest Higgs production rate, high QCD background. Vector boson fusion lower rate, lower background. Higgs Decays. For low Higgs mass is the most important decay.

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Particle Physics 735 Spring 2007

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  1. Christos Lazaridis, Particle Physics 735 A study on... Particle Physics 735 Spring 2007

  2. Christos Lazaridis, Particle Physics 735 Higgs Production • Gluon-gluon fusionhighest Higgs production rate, high QCD background • Vector boson fusion lower rate, lower background

  3. Christos Lazaridis, Particle Physics 735 Higgs Decays • For low Higgs mass is the most important decay • For higher Higgs masses WW is the most important decay (wait for Kira’s talk!) • A Higgs mass of 300 GeV was chosen for this study

  4. ISUB Which? 24 fi fibarZh0 26 fi fjbarW+h0 102 ggh0 123 fifj -> fifjh0 124 fifj -> fkflh0 Signal Characteristics • Higgs→ZZ→e+e-νν • Turned off all Higgs decays except the desired one • Cross section: • 6.60*10-11 mb Pythia parameters: Christos Lazaridis, Particle Physics 735

  5. Christos Lazaridis, Particle Physics 735 ISUB Which? 15 fifibargZ 16 fifjbargZ 30 figfiZ Background Characteristics • 4 Background sets: • Single Z • Total cross section: • 5.35x10-3 mb Pythia parameters:

  6. Christos Lazaridis, Particle Physics 735 ISUB Which? 19 fifibarγZ 22 fifibarZZ 23 fifjbarZW+ 25 fifibarW+W- Background Characteristics • 4 Background sets: • Vector Boson fusion • Total cross section: • 2.35x10-5 mb Pythia parameters:

  7. Christos Lazaridis, Particle Physics 735 ISUB Which? 81 fifibarQkQkbar 82 ggQkQkbar Background Characteristics • 4 Background sets: • Top quark • Total cross section: • 6.88x10-6 mb Pythia parameters:

  8. Christos Lazaridis, Particle Physics 735 ISUB Which? 1 fifibarγ*/ Z Background Characteristics • 4 Background sets: • Drell-Yan • Total cross section: • 3.27x10-3 mb Pythia parameters:

  9. Christos Lazaridis, Particle Physics 735 The CMS Detector

  10. Christos Lazaridis, Particle Physics 735 Procedure to identify electrons • Iterating over all SuperClusters • Ignoring all SCs with very low or very high energy • Comparing each SC with all Jets • If there is no near Jet or the SC has most of the energy then • We compare the SC with all tracks. Tracks of very low Pt are ignored. • If there is a track close enough and the ratio of ESC/Pt,Track is above a certain threshold then we can officially declare that SC as an electron candidate

  11. Christos Lazaridis, Particle Physics 735 Cuts to identify electrons Starting with 2060 Events : 12705 Initial SCs } 10278 Remain (80.9%) • Min SC energy cut = 5.0 GeV • Max SC energy cut = 500.0 GeV • ΔR between SCs & Jets ≥ 0.15 • E ratio between SCs & Jets ≥ 0.85 • Track Pt Cut ≥ 10 GeV • ΔR between Tracks & SCs ≤ 0.15 • E/Pt between Tracks & SCs ≥ 0.7 } 7015 Remain (55.2%) } 3493 Remain (27.5%)

  12. Christos Lazaridis, Particle Physics 735 Jet ΔR Cut ΔR between SCs & Closest Jet

  13. Christos Lazaridis, Particle Physics 735 Track ΔR Cut ΔR between Scs & Closest Track

  14. Generated Electrons Christos Lazaridis, Particle Physics 735

  15. Christos Lazaridis, Particle Physics 735 Electron Candidates Et (GeV)

  16. Christos Lazaridis, Particle Physics 735 Generated vs Reconstructed η Minimal matching: Ereco = 0.8~1.2 Egene

  17. Christos Lazaridis, Particle Physics 735 Generated vs Reconstructed φ Minimal matching: Ereco = 0.8~1.2 Egene

  18. Christos Lazaridis, Particle Physics 735 Variable Selects against... Z mass WW, Top, Drell-Yan Electron Et Fake electron, combinatoric Z Pt Fake Z Missing Et Z bg (maybe not top or W) Higgs Selection Variables • Higgs→ZZ→e+e-νν main backgrounds: • Single Z • Vector Boson fusion • Top • Drell-Yan

  19. Christos Lazaridis, Particle Physics 735 Signal/Bg comparison(only 2 bg sets) Electron Candidates Et (GeV)

  20. Christos Lazaridis, Particle Physics 735 Missing Et(Generated vs. Reconstructed)

  21. Christos Lazaridis, Particle Physics 735 Z Invariant Mass Inv. Mass (GeV/c2)

  22. The end! Summary • Is an interesting Higgs channel to work with • The backgrounds are high, but using the selection variables mentioned, can be significantly reduced • Using our home-made electron finder we’ve had a pretty good yield (84.8% of expected electrons were found and with good agreement to the generated set). Using the advanced algorithms implemented within CMMSW we can do better Christos Lazaridis, Particle Physics 735

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