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CDF 実験でのヒッグス粒子の研究

CDF 実験でのヒッグス粒子の研究. 佐藤構二， CDF Collaboration 日本物理学会　２０１３年秋季大会 高知大学， ２０１３年９月２１日. Tevatron Run II. collisions at s = 1.96 TeV (1.8 TeV in Run I). Run II: Summer 2001 - Autumn 2011. Collisions at world highest energy until Nov 2009. Energy frontier for ～ 25 years!!

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CDF 実験でのヒッグス粒子の研究

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  1. CDF実験でのヒッグス粒子の研究 佐藤構二， CDF Collaboration 日本物理学会　２０１３年秋季大会 高知大学，２０１３年９月２１日

  2. Tevatron Run II • collisions at s = 1.96 TeV(1.8 TeV in Run I). • Run II: Summer 2001 - Autumn 2011. • Collisions at world highest energy until Nov 2009. • Energy frontier for ～25 years!! • Two detectors (CDF and D0) for wide range of physics studies. • Delivered: 12 fb-1. • Recorded by CDF: 10 fb-1. • Recorded by D0: 10 fb-1.

  3. CDF and D0 Detectors • Both are multipurpose detectors: • Top/EWK measurements, Searches for Higgs and New Phenomena, and B physics. • Precision tracking with Silicon in 1.5 (CDF)/1.9 T (D0) Solenoid field. • EM/Had calorimeters for e/g/jet measurement. • Outer muon chambers. D0 CDF

  4. Constraint on Higgs Mass • Mass of Top Quark (World Average): Tevatron Run I result： mtop = 178.0  4.3 GeV/c2 With Tevatron Run II results： mtop = 173.2  0.9 GeV/c2 • Mass of W Boson (World Average): Before Tevatron Run II： mW=80.426±0.034 GeV/c2 With Tevatron Run II results： mW=80.385±0.015 GeV/c2 Before Tevatron Run II results (Spring 2004) With Tevatron Run II results (Winter2013) • Mhiggs<152GeV/c2 （95% CL) . • ….was Mhiggs<251 GeV/c2(95% CL) in Spring 2004.

  5. Higgs Discovery by LHC, Summer 2012 ATLAS: 5.9 σ from Background CMS: 5.0 σ from Background Discovery was driven by and decay modes.

  6. What We Want to Remember!! TEVATRON Summer 2012: Excessat GeV/c2 mass region. 3.1 σ from Background in Combination of searches for analyses. Complementary to LHC results Discovery was driven by and decay modes.

  7. Tevatron Winter 2013 Combination • Final full combination of Tevatron Higgs searches. • Published on Sep 17: • CDF: Phys. Rev. D 88, 052013 (2013). • D0: Phys. Rev. D 88, 052011 (2013). • CDF&D0: Phys. Rev. D 88, 052014 (2013). • Although we know from LHC results, we present our search results over full mass range. • Analysis updates in a few channels since last Summer. • Studies of Higgs couplings to Fermions and Bosons.

  8. SM Higgs Production and Decay at Tevatron Channels with best sensitivity are: • mH<135 GeV (low mass): • gg→H→bb is difficult to see. • Look for WH/ZH with leptonic vector boson decays. • mH>135 GeV (high mass): • Easiest to look for H→WW→lnln.

  9. CDF and D0 analyses

  10. CDF: Analysis • NN B-tagging algorithm. • Two operation points (T/L). • Subdivision of events to 4 b-tag categories (TT/TL/Tx/LL) • Trained 3 NN to further subdivide analysis sample. • Separate signal from , +jets, diboson. • Final discrimintnt NN trained to separate signal from all backgrounds. • or + 2 or 3 jets. • / trigger + MET trigger (for ’s which trigger failed to identify). Final Discriminant = separate Signal from all Bkgd. +jets like diboson like signal like like Candidate event NN Diboson NN +jetsNN

  11. General Strategy for Improved Sensitivity • Utilize Multivariate Algorithms (MVA) for better S/B separation. • Neural Net, Boosted Decision Tree, Matrix Element, etc. • Training of multiple MVAs in many channels. • Maximize trigger efficiency of each analysis. • Analysis of events through different triggers. • Maximize acceptance of leptons. • Use isolated tracks as low quality lepton candidates. • Improved b-tagging (low mass analyses) • Algorithms based on MVA. • Divide analysis sample into high/low purity subsamples. • Subdivision due to lepton and b-tag quality.

  12. History of Analysis Improvement • Tevatron analyses have been constantly improved. • Improvement is far better than expected due to increase in data!! Expected sensitivity for CDF searches:

  13. CDF and D0: Combined Limit CDF D0 D0 excludes (95% C.L.): 90 < mH < 101 GeV/c2 157 < mH < 178 GeV/c2 Expected exclusion (95% C.L.): 155< mH < 175 GeV/c2 CDF excludes (95% C.L.): 90 < mH < 102 GeV/c2 149 < mH < 172 GeV/c2 Expected exclusion (95% C.L.): 90 < mH < 94,96 < mH < 106 GeV/c2 153 < mH < 175 GeV/c2

  14. CDF+D0 Combined Limit Tevatron excludes: 90<mH<109, 149<mH<182 GeV/c2 Expected exclusion: 90<mH<120, 140<mH< 184 GeV/c2 Broad excess at 115-140 GeV/c2 Corresponding to 3.0σ for mH=125 GeV/c2

  15. Signal Cross Section Best Fit • for . • Consistent across different decay modes. • Assuming the SM Higgs branching ratio: • Fit separately by decay mode for :

  16. Studies of Higgs Couplings • Coupling scale factor w.r.t. SM: • Kf : Fermion coupling Hff • KW, KZ, KV : Boson couplings HWW, HZZ, HVV KZ • Follow prescription of LHC Higgs working group arxiv:1209.0040. • Assume a SM-like Higgs particle of 125 GeV. Kf KW Kf

  17. Test of Custodial Symmetry • floating. • Compute posterior probability density for . SM

  18. Constraint on HVV and Hff Couplings • Assuming: • Result is consistent with SM. • Preferred regions around , • Negative values preferred for due to excess.

  19. Summary • Extensive search for Higgs boson with full Tevatron dataset. • Analyses evolved throughout Run II. • Excluded: 90<mH<109, 149<mH<182 GeV/c2(95% C.L.) • Observed a broad excess in115<mH<140 GeV/c2. • Higgs Mass consistent with LHC. • 3.0 standard deviations at . • Excess is shared between CDF and D0. • Excess mainly from . • for . • Studies of Fermion and Boson couplings. • Consistent with SM expectations. • Complementary to LHC studies.

  20. Backup

  21. Distribution of the Candidate Events Candidate events in all the combined analyses: Data - Background

  22. P-value of the Tevatron Combination • 3.0 standard deviations at .

  23. D0: Channel • , or pair within GeV. • BDT to reject in , events. • are considered as signal. • Events with different jet multiplicity have different s/b composition. • Separately analyze 0, 1, ≥2 jet bins. • Subdivision of sample into WW-enriched/depleted by WW-BDT. • Train a final BDT discriminant against all background. Distributions of the Final discriminant (only showing channel): 0 jet WW-enriched 0 jet WW-depled ≥2 jet

  24. Tevatron Combination by Channel

  25. Sensitivity of Individual Channel Old plot, just for illustration purposes

  26. Summer 2012 Summer 2012 HCP 27

  27. Improved b-tagging Jet Displaced Tracks CDF and D0 combine information of secondary vertex and tracks within jet cone by MVA (NN and BDT). Secondary Vertex Primary Vertex

  28. B-jet energy correction by NN(CDF llbb channel) After NN Correction: Before NN Correction: Resolution on

  29. Systematics (CDF llbb channel) • The effect of Jet Energy Scale on the distribution shape is also considered. • SysyrmsticuncertaintydegradesensitivitytoZHsignalbyapproximately13%.

  30. 2013 Collected Event Distribution Tevatron CDF D0

  31. 2013 Best Fit Tevatron CDF D0

  32. HWW, HZZ and Hff Couplings , or Negative values preferred for and due to excess.

  33. HWW and HZZ Couplings • floating. • Result is consistent with SM. • Preferred region around:

  34. Limits by Experiment D0 CDF

  35. CDF H->γγ

  36. Coupling Factor for 2 KW Kf +

  37. D0 Spin and Parity Measurement • LHC results in bosonic decay modes favor . • Tevatron sensitive in decay mode. • Visible mass of system is sensitive to assignment. - J. Ellis et al., JHEP 1211, 134 (2012)

  38. D0 Spin and Parity Measurement 2 • , H1=(+bkg) / H0=(+bkg). • Exclude at 99.9% C.L. (in favor of ). • Suppose excess is admixture of and particles: • Exclude fraction at 95% C.L (in favor of pure ).

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