1. 1 Viktor Veszprémi (Purdue University, CDF Collaboration) SUSY 2005, Durham Search for the SM Higgs Boson at the CDF Experiment Search for the SM Higgs Boson at the CDF Experiment

2. 2 Gluon fusion: Large cross section But no search potential below M h =~135 GeV Indistinctive signature of a pair of b-jets Signal swamps in QCD multi-jet processes “Higgsstrahlung” (W/Z associated production): Smaller cross section Good search potential both at lower and higher Higgs mass Easier to trigger on the decay products of the W/Z bosons Viktor Veszprémi, SUSY 2005, Durham Standard Model Higgs Production

3. 3 m H <114.4 GeV Excluded at 95 % C.L. EWK fits prefer light SM Higgs < ~260 GeV Excluded M h (GeV) Exluced by LEP H->bb dominated region: 2 analyses with results 1 analysis in progress H->WW dominated region: 2 analysis result Viktor Veszprémi, SUSY 2005, Durham Standard Model Higgs Decay Modes

4. 4 Charged l epton final states: Low Higgs mass scenario Requires good b-jet selection, lepton identification, Missing Et reconstruction, di-jet invariant mass reconstruction High Higgs mass scenario Requires efficient lepton identification Final state with no charged leptons and low Higgs mass: Requires good b-jet selection, Missing Et reconstruction, di-jet invariant mass reconstruction Viktor Veszprémi, SUSY 2005, Durham, England CDF SM Higgs Analyses

5. 5 Tagging B-jets Tagging jets with the SecVtx algorithm is a powerful way of selecting b-jets Jet is tagged: decay length L xy /  Lxy > 7 L xy >0 identifies real heavy flavor jet Tagged jet Prim. vertex 2 nd vertex L xy >0 Currently using the tight tagger Development of a “forward b-jet tagging” is in progress to increase acceptance Mistag rate is ~1% Viktor Veszprémi, SUSY 2005, Durham, England

6. 6 Reconstuction of Z decaying to b-jets –Measure jet energy scale and resolution –Provides a tool for investigating b-jet specific jet energy corrections Looking for Z in double tagged events with –no additional jets above 10 GeV –Jets are back-to-back topology 3394±515 Z  bb events were found in a sample of 85,784 double-tagged events. (333pb -1 ) We can observe the Z peak Reconstruction of Z  bb decays in CDF Viktor Veszprémi, SUSY 2005, Durham, England

7. 7 W+W+ e+e+ W-W- e-e- n Event Selection: exactly two identified leptons (veto WZ, ZZ) no jets with E t > 15 GeV and |  | < 2.5 (veto top- pairs) > 25 GeV If < 50 GeV: (veto Z/  ) not 76 < M ee/uu < 106 unless Missing E T significance larger than 3 (veto WZ,ZZ,Z/  ) leptons having opposite charge signs (veto WZ) di-lepton invariant mass M ll < half the Higgs mass. (discriminates from WW, WZ, ZZ) Spin of Higgs is 0 W spins are anti-parallel Leptons from W’s are aligned Di-lepton mass is constrained Viktor Veszprémi, SUSY 2005, Durham, England

8. 8 (SM) source Expectation (M h =180 GeV) WW6.49 +/- 0.76 WZ0.18 +/- 0.02 ZZ0.06 +/- 0.01 Drell-Yan ee0.87 +/- 0.44 DY mumu0.43 +/- 0.19 DY tautau0.03 +/- 0.01 ttbar0.02 +/- 0.01 fakes0.81 +/- 0.25 total bg8.90 +/- 0.98 HWW0.17 +/- 0.02 data8 Small di-lepton invariant mass Leptons originating from the signal process tend to be back-to-back in the transverse plain Viktor Veszprémi, SUSY 2005, Durham, England

9. 9 Clustered mass: The 95% C.L. effective cross- section limit of the Higgs boson Viktor Veszprémi, SUSY 2005, Durham, England

10. 10 Like-sign di-lepton selection (“1”=more, “2”=less energetic) p T,1 >20 GeV, p T,2 >6 GeV reject conversions, cosmics, Z  leptons Signal region: p T,2 >16 GeV, for m H <160 GeV Harden p T,2 cut to 18 GeV for m H >160 GeV CategoryEvents in 193.5 pb -1 Conversions 0.61  0.61 Fake Leptons 0.12  0.01 Other sources * 0.22  0.10 Total background 0.95  0.64 Data0 * Other backgrounds: Di-boson, top, Wqq SM WH signal: 0.03 events (m H =160 GeV) Viktor Veszprémi, SUSY 2005, Durham, England

11. 11 Results Viktor Veszprémi, SUSY 2005, Durham, England Acceptance includes W branching fractions

12. 12 Signature: isolated lepton with E T > 20 GeV or pt > 20 GeV in |  |<1.0 Missing E T > 20 GeV 2 taggable jets (require 1 or 2 tags) Below is a double-tagged WH event Applied selection: Events with an additional lepton with sign opposite to the primary is removed (Z and conversion removal) 2-jet bin contains the signal inclusive single / exclusive double tag is required -> single tag search is more sensitive Viktor Veszprémi, SUSY 2005, Durham, England

13. 13 Background SourceEvents in 319 pb -1 W+light flavor39.3  3.1 54.0  18.4 19.5  6.6 16.8  4.3 Di-boson+Z  +  - 5.0  1.1 Non-W16.5  3.2 14.1  2.5 9.6  2.0 Total Background174.7  26.3 Observed Data187 Viktor Veszprémi, SUSY 2005, Durham, England Number of background events in the 2-jet bin: W+h.f. normalization SignalTop background normalization

14. 14 Dijet invariant mass in the inclusive single tag sample The 95 % C.L. limit set on the effective cross-section of the Higgs boson Viktor Veszprémi, SUSY 2005, Durham, England

15. 15 Z-> ν ν, H-> b b Signal has a distinctive topology Large missing transverse energy two jets (one is b-tagged) Missing E T b-jet y x This signature proved to be the most sensitive in the Run I and recent analyses at CDF Viktor Veszprémi, SUSY 2005, Durham, England Basic Selection cuts: Jet requirements 1 st Jet E T > 40 GeV 2 nd Jet E T > 20 GeV No other jet with E T > 15 GeV E T > 70 GeV Minimum 1 b-tag

16. 16 Analysis Outline We performed a blind analysis Extended Signal Region Veto events with leptons Missing E T and 2 nd leading jet are not parallel Cut optimization is performed in this region based on Monte Carlo simulation before looking at the real data Viktor Veszprémi, SUSY 2005, Durham, England Control Region 1 – QCD h.f. Veto events with identified leptons Missing E T and 2 nd leading jet are parallel Control Region 2 – EWK Require min. 1 lepton Missing E T and 2 nd leading jets are not parallel Optimized cuts are tested in this region before looking at the real data in the Signal Region

17. 17 QCD heavy flavor normalization Control Region 1: QCD multi-jet is the most dominant process because of its large cross-section A good description of this background allows us to efficiently reduce it with optimized cuts Viktor Veszprémi, SUSY 2005, Durham, England 2 nd jet Fake Missing E T 1 st jet ~180 o A di-jet QCD event: QCD events also have a particular topology: jets are back-to-back “Missing E T “ points along the leading jet Events are simulated by a b-filtered Pythia Monte Carlo sample which is normalized to data Mistags (tagged light flavor jet events) are estimated from Data before tagging

18. 18 Cut Optimization Viktor Veszprémi, SUSY 2005, Durham, England The following optimized cuts were developed on a benchmark signal MC sample (M h =120 GeV) Selection cutZH 120 288.9 pb -1 Acceptance (%) Basic Cuts 0.205  0.00355.92  0.1 0.026 0.205  0.00355.92  0.1 0.027 significance 0.183  0.00335.23  0.095 0.031 0.161  0.00314.68  0.089 0.037 Di-jet mass cut 0.126  0.0163.64  0.079 0.062 The last selection is on the di-jet mass. A  20 GeV mass window is applied to the data and Monte Carlo around the reconstructed Higgs mass peak Performed a counting experiment

19. 19 Result Viktor Veszprémi, SUSY 2005, Durham, England The top plot : di-jet invariant mass in Control Region 2 after optimization, before the mass- window cut The bottom plot is the same in the Signal Region For the 120 GeV Higgs mass we apply a 80-120 GeV window cut: SM background prediction: 4.36  1.02 events QCD : 11.4% Top : 20.5% EWK : 18.2% Light flavor mistag: 50% Observed: 6 events. With a 95 % C.L. we expect the limit to be for the Observed limit:

20. 20 Signal Event Candidate Viktor Veszprémi, SUSY 2005, Durham, England Data events from Signal Region passing all selection cuts candidate in the 80-120 GeV mass window Double-tagged event Missing E T 144.8 GeV Di-jet invariant mass = 82 GeV Leading Jet E T = 100.3 GeV Second Jet E T = 54.7 GeV

21. 21 Summary of Limits set at CDF Viktor Veszprémi, SUSY 2005, Durham, England First analysis with 200-300 pb -1 data completed Nearly 1 fb -1 on CDF tape Estimate sensitivity: 2 fb -1 : exclude Higgs up to mass of 120 GeV 8 fb -1 : exclude Higgs up to mass of 135 GeV

22. 22 Backup Slides

23. 23 FY02 FY03 FY04 FY05 Increasing Tevatron Luminosity Viktor Veszprémi, SUSY 2005, Durham, England Tevatron 8 fb -1 Tevatron 2 fb -1 LEP excluded Future expectations based on the Higgs sensitivity study in 2003. Below is the instantaneous and integrated luminosities recorded at CDF so far

24. 24 Missing E T Reconstruction 2 nd jet Fake Missing E T 1 st jet 180 o A di-jet QCD event: QCD events also have a particular topology: jets are back-to-back Fake missing E T points along the leading jet Real missing E T – produced by undetected particles Neutrinos Fake missing E T Beam/detector effects A set of clean-up cuts are applied to eliminate beam effects Unbalanced, mis-measured jets The primary source of E T in QCD events Since the cross-section of QCD is large, most of the triggered events are like this Makes QCD the main background : Viktor Veszprémi, SUSY05, Durham, England