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Higgs Searches at CDF

Higgs Searches at CDF. Alexei Safonov (Texas A&M University) For the CDF Collaboration. Outline. Brief introduction to Higgs search strategies at the Tevatron Summer 2011 combination and ingredients New CDF analyses since Summer 2011 Ongoing work and plans Summary.

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Higgs Searches at CDF

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  1. Higgs Searches at CDF Alexei Safonov (Texas A&M University) For the CDF Collaboration

  2. Outline Brief introduction to Higgs search strategies at the Tevatron Summer 2011 combination and ingredients New CDF analyses since Summer 2011 Ongoing work and plans Summary “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012

  3. Higgs Production at Tevatron • Dominated by gluon fusion • But large decay modes often come with large backgrounds • Associated Production • While smaller cross section, offers cleaner final states • Vector Boson Fusion (VBF) • Even smaller cross-section, but can help increase the overall sensitivity • Have to use all accessible modes and many decay channels • Improving analysis techniques “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012

  4. Higgs Search Strategies Sensitivity strongly depends on backgrounds for a specific channel: “High mass” m >~135 GeV: WW (and ZZ) decay modes Clean final states with leptons, any production mode will do “Low mass” m < ~135 GeV: Associated production WH/ZH: Rely on leptons/neutrinos to reduce background, go after all decay modes (but bb dominates) Gluon fusion: H→bb overwhelmed by backgrounds H→tt: ok, but small BR “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012

  5. Summer 2011 Combination “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 Of course LHC results since then excluded masses above ~135 GeV

  6. Ingredients of the Combination ZH→llbb WH→lnbb H→WW VH→MET+bb “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • High mass region dominated by H→WW • Low mass region: • WH+ZH→MET+bb • WH→lnbb • ZH→llbb • H→WW makes key impact above 120 GeV

  7. Selected Recent Analyses “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012

  8. Search for H→with 10 fb-1 • Fit for a bump plus a smooth curve (from the rest of the distribution after excluding 12 GeV window around searched Higgs mass) • Each of 4 categories separately “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • One of very recently updated results • Follows the same technique as the 7 fb-1 analysis • At least one central photon ET>25 GeV • Many improvements including NN ID for central photons, converted photon recovery in central region

  9. Search for H→with 10 fb-1 “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Combine four channels at the level of likelihoods • Bayesian limits for mH)<130 GeV at ~12xs(SM) except m~120 GeV • Previous limit used in the combination was ~14-19xs(SM)

  10. Search for H→ w/ 1+ Jets “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Result from Fall’11, L=8.3 fb-1 • Allow multiple production modes • Sensitivity dominated by VH (H→, V→jets) • Channels: e/m+t+1jet,e/m+t+≥2jets, e+m+1jet, e+m+≥2jets, • Deploy Support Vector Machine (SVM) to discriminate against main backgrounds using event kinematics properties: • Z→+jets • tt-bar (only for em+jets channel) • QCD muti-jets • Fit the distribution for the SVM outcome to extract limits(or claim discovery if there is significant excess)

  11. SVM-Based H→ Search Limits “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Final exclusion limit is obtained by combining the four channels at the level of likelihoods • Observed limit about 12xs(SM) • Combined limit is dominated by e/m+t+≥2jets channel

  12. Search for H→ Using MMC “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Also a recent analysis using L=7.8 fb-1 • Traditional cut-based search, but attempts to improve di-tau mass reconstruction using MMC technique • Elagin, Murat, Pranko, and A.S., NIM A654, 481 (2011) • MMC uses likelihood to solve an under-constrained system of equations • Uses Bayesian-like priors to pick solutions consistent with tau decay kinematics and experimental uncertainties in measuring MET • A large improvement over collinear approximation as MMC can handle back-to-back events (and no tail)

  13. Search for H→ Using MMC e+th channel Npr(t)=1 Njet=0 e+th channel Npr(t)=3 Njet=0 “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Attempt to minimize systematic uncertainties due to backgrounds by measuring normalizations from data • Require one of two taus to decay leptonically, another hadronically • No e+m events in this search • Define 8 channels: • (1 or 3 prong) x (e/m) x (0/1+jets) • Count jets with ET>30 GeV • Fit ditau mass reconstructed with MMC for signal + background

  14. Search for H→ Using MMC e+th channel Npr(t)=1 m+th channel Npr(t)=1 Njet>0 e+th channel Npr(t)=3 m+th channel Npr(t)=3 “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Use of MMC equivalent to ~x1.6 more data vs transverse mass • Sub-channel with Njet>0 is sensitive to VH production, reach can be further improved by utilizing kinematics selections (will be in 10 fb-1 analysis)

  15. Search for H→ Using MMC “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Combined limit of 8 channels: ~14xs(SM)@m=115 GeV/c2 • 0-jet and “1+”-jet channels complementary • Updated analysis will use improved event kinematics discrimination

  16. Near Future Plans “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012

  17. Are We Done Yet? • Expect sensitivity scaling better than 1/sqrt(L) due to ongoing improvements to analyses “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Luminosity used in key channels: • H→WW: 8.2 fb-1 • WH+ZH→MET+bb: 7.8 fb-1 • WH→lnbb: 7.5 fb-1 • ZH→llbb: 7.5-7.9 fb-1 • Less in secondary channels: weighted luminosity for low mass searches is ~7.5 fb-1 • CDF full certified dataset is now 10 fb-1 • Expect updated analyses showing up at La Thuile, Tevatron combination is more likely to be shown at Moriond

  18. Tevatron and LHC Expectations • Tevatron data will allow important cross-checks and help answer questions that may not be answered by the LHC alone until after the long shutdown in 2012 “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • Why bother if the LHC expects to settle the question by the end of 2012? • Will we know if what we found is indeed the SM Higgs? • E.g. branching for H→bb: • Current CMS expected limit is 3-4xs(SM) for the bb channel • Complementary sensitivity in the very low mass range • E.g. plot on the right: region below 120 seems already excluded by CMS+Tevatron

  19. Summary “Higgs Searches at CDF”, A. Safonov, Aspen, CO, February 14, 2012 • CDF is busy updating its results to include the full 10 fb-1 dataset • Numerous improvements to analysis techniques are expected to improve sensitivity beyond just √L • Expect to see individual analyses at La Thuile, combination is more likely to be first presented at Moriond • Apart from complementarity to global LHC+Tevatron sensitivity, Tevatron results will have an impact on our understanding the nature of Higgs should it be discovered at the LHC in 2012 • One example is sensitivity to the H→bb mode, which is an important check-mark in distinguishing between SM non-SM Higgs cases

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