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Searches for H→bb at DØ

Searches for H→bb at DØ. Satish Desai - Fermilab on behalf of the DØ Collaboration 36th International Conference on High Energy Physics Melbourne, Australia, 2012. As of Last Week. M H < 152 GeV (indirect constraints) 122 < M H < 127 GeV (searches). The Search Strategy. Main Decay: H→bb.

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Searches for H→bb at DØ

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  1. Searches for H→bb at DØ • Satish Desai - Fermilab • on behalf of the DØ Collaboration • 36th International Conference on High Energy Physics • Melbourne, Australia, 2012

  2. As of Last Week MH < 152 GeV (indirect constraints) 122 < MH < 127 GeV (searches)

  3. The Search Strategy Main Decay: H→bb

  4. The Search Strategy W+jets backgrounds even worse at LHC: Sensitivity at H→γγ/ZZ Main Decay: H→bb

  5. The Search Strategy Tevatron can still make important contributions for H→bb W+jets backgrounds even worse at LHC: Sensitivity at H→γγ/ZZ Main Decay: H→bb

  6. Search Ingredients • Maximize acceptance and efficiency • Efficient b-tagging • Split into subsamples with different purities • Multivariate Techniques llbb lνbb ννbb

  7. Increasing Acceptance Expanded event selection 5-6% acceptance increase for WH→μνbb 6% acceptance increase for ZH→llbb llbb Analysis WH Analysis

  8. More b-tagging Categories Displayed Track Decay Vertex Primary Collision WH Analysis

  9. More b-tagging Categories Switch from 3→4 b-tag categories Sensitivity Gain: 4-5% Displayed Track Decay Vertex Primary Collision WH Analysis

  10. Targeting Top 7-8% improvement in sensitivity llbb Analysis Remove 45% of background Keep 94% of signal Still used as extra sample

  11. Multivariate Techniques Add new variables Improved training procedures Sensitivity Improvements: 4-5% for lvbb 10% for vvbb More optimal vvbb Analysis vvbb Analysis WH Analysis

  12. Validation with Dibosons Search for WZ/ZZ→X+bb Same final state as WH/ZH→X+bb searches Cross section is five times larger Use same search strategy: Same event selection Same multivariate discriminants Same statistical analysis tools Seeing this signal is a crucial test of analysis techniques DØ only combination Significance: 3.3σ Tevatron combination Significance: 4.6σ Cross section: Measure: 4.5±0.6±0.7 pb Theory: 4.4±0.3 pb See talk by B. Penning

  13. Results Limits at MH=115 GeV Exp: 1.58×σSM Obs: 1.96×σSM Limits at MH=125 GeV Exp: 2.25×σSM Obs: 3.30×σSM Overall sensitivity improves by 10-15%

  14. The Log Likelihood Ratio Observed Signal+Background Background Test statistic used for CLs Method Separation between points acts like Δχ2 of fits to models Based on Poisson likelihoods for two hypotheses: signal+background background only Log likelihood ratio acts like Δχ2 of fits to models

  15. Summary • Tevatron sensitivity to H→bb complements LHC results • Evidence for VZ→X+bb used as a proving ground for H→bb search • Modest excess for MH>120 GeV • See additional Tevatron Higgs talks at this conference • Finalizing results now http://www-d0.fnal.gov/Run2Physics/WWW/results/higgs.htm

  16. Searching through the years 2007 2010 2008 2011 Spring 2012 2009

  17. Results for ZH→ννbb

  18. Results for ZH→llbb

  19. Results for WH→lνbb

  20. S/B Distributions Spring 2012 Summer 2012 Spring 2012 Summer 2012

  21. Accumulated Signal Spring 2012 Summer 2012 Spring 2012 Summer 2012

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