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Optimizing Higgs Analysis at DØ

Optimizing Higgs Analysis at DØ. John Sandy – SULI Intern (Texas Tech University) Mentors: Michael P Cooke and Ryuji Yamada (Fermilab National Accelerator Laboratory). Optimizing Higgs Analysis at DØ. Physics – The Standard Model and the Higgs Mechanism.

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Optimizing Higgs Analysis at DØ

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  1. Optimizing Higgs Analysis at DØ John Sandy – SULI Intern (Texas Tech University) Mentors: Michael P Cooke and Ryuji Yamada (Fermilab National Accelerator Laboratory)

  2. Optimizing Higgs Analysis at DØ Physics – The Standard Model and the Higgs Mechanism • The Standard Model of Particle Physics: • Three generations of matter • Quarks and Leptons • Force Carriers Initially predicted that particles should be massless! Peter Higgs and his colleagues (Englert, Brout, Guralnik, Hagen, Kibble) came to rescue in 1964 and introduced what is now known as the Higgs Mechanism.

  3. Optimizing Higgs Analysis at DØ The Higgs Boson • Excitation of the Higgs field (analogous to photon in E&M field) • Gives mass to all particles • Interacts more frequently with more massive particles, attributing more mass to them Less massive More massive . The Higgs Field Two particles attempting to move across the Higgs Field

  4. Optimizing Higgs Analysis at DØ Higgs Boson Signal vs. Background The Higgs boson has been notoriously difficult to search for: • Complex, mass dependant branching ratios • Lots of SM backgrounds • Low production rates

  5. Optimizing Higgs Analysis at DØ The Tevatron provided proton-antiproton collisions with a center of mass (CM) energy of 1.96 TeV The DØ Detector • Inner silicon detector • Scintillating fiber tracking system • 2 tesla solenoid • Uranium liquid argon calorimeter • Large muon system • 900,000 individual channels

  6. Optimizing Higgs Analysis at DØ Event Displays with D0Cafvis

  7. Optimizing Higgs Analysis at DØ The Higgs Boson Search at DØ My search is focused on four Higgs final states: H → WW → lνlν WH → lνbb • Pre-selection: • Triggering • Lepton Tagging • “b-tagging” Electron / muon events ZH → llbb ZH → ννbb 0tag, 1tag, 2tag, loose, medium, tight 7

  8. Optimizing Higgs Analysis at DØ The Higgs Boson Search at DØ Boosted Decision Trees (BDTs) Massjj > 120 BDT makes cuts based on signal purity parameters Bins that pass more cuts have higher signal to background ratio Pass Fail Never throw out any data, so no chance of losing signal ? ? f p f p … and so on … S / B

  9. Optimizing Higgs Analysis at DØ Using BDTs to train Multi-Variate Analyses (MVAs) I used BDTs to train MVAs for separating Higgs boson signal from the tt, V + jets, and VV backgrounds Create a variable list to build a BDT Run analysis framework and prune variable list: • Variable Importance • Variable Correlation • Variable Modeling ….

  10. Optimizing Higgs Analysis at DØ Using BDTs to train Multi-Variate Analyses (MVAs) Variable modeling based on simulation: Well modeled Poorly modeled

  11. Optimizing Higgs Analysis at DØ Using BDTs to train Multi-Variate Analyses (MVAs) BDTs expected signal and background separation Multijet training that I am helping train My own training for Higgs vs. VV background discrimination

  12. Optimizing Higgs Analysis at DØ Final BDTs (Low Mass) After training, the final BDTs are produced and can be used to separate signal from background

  13. Optimizing Higgs Analysis at DØ Final BDTs (High Mass)

  14. Optimizing Higgs Analysis at DØ Final BDTs for 2-Tight Tag Events (Low Mass)

  15. Optimizing Higgs Analysis at DØ Conclusions Recompiled D0Cafvis will allow DØ collaborators to use event displays in future talks and presentations (already been used at DØ collaboration meeting in UK) The training of secondary MVAs has shown improvement in other channels (4jet) Further training may improve modeling When training is fully completed, improved MVAs will improve overall Higgs search at the Tevatron, allowing for stronger results On July 4th CERN announced a new “Higgs like” particle using γγ and Z-Z channels DØ and CDF recently published results claiming evidence for such a particle using the bb channel

  16. Optimizing Higgs Analysis at DØ Acknowledgments This work was supported by the Experimental Particle Physics Division at Fermilab National Accelerator Laboratory, U.S Department of Energy Office of Science’s and Office of Workforce Development for Teachers and Scientists. I would like to thank my mentors Ryuji Yamada and Michael P. Cooke. I would also like to thank Anthony Podkowa and Herb Greenlee for their assistance.

  17. Optimizing Higgs Analysis at DØ Backup

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