La ricerca dell Higgs Standard Model a CDF

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1 La ricerca dell Higgs Standard Model a CDF Melisa Rossi INFN-TS Giornata di seminari INFN Trieste - 7 Luglio 2009

3 FNAL: Fermi National Accelerator Lab Tevatron currently provides the highest energy proton-antiproton collisions in the world: = 1.96 TeV

8 years Tevatron is performing really well Record Peak Ist. Luminosity 3.

4 Tevatron Performance 3.5x10 32 more than 100 times data at disposal now than used for the top quark discovery 8 years Tevatron is performing really well Record Peak Ist. Luminosity 3.6x10 32 cm -2 s -1 Record luminosity per week 73 pb -1 Record luminosity per month 250 pb -1 Total Luminosity delivered 6.9 fb -1 more than 2 fb -1 delivered in 2008

15% pt EM and HAD calorimeters - EM energies

5 Collider Detector at Fermilab 1.4 T SC Solenoid Silicon Vertex 30µm resolution on impact parameter Central Tracker: COT resolution: 0.15% pt EM and HAD calorimeters - EM energies (γ,e): σ/et = 13.5%/ ET+1.5% HAD energies(π±): σ/et = 50%/ ET+3% Muon systems 3-level trigger system

6 Higgs The Standard Model needs the Higgs mechanism to generate the boson and fermion masses. The SM cannot predict m H, but can correlate it with m W and m top this allows to set model dependent constraints based on the measured values of m W and m top current global fits constrain m H <163 GeV/c 2 at 95% CL LEP excluded at 95% CL an Higgs with m H <114 GeV/c 2 by direct searches Tevatron can observe/exclude the Higgs in m H [100,200] GeV/c 2 which covers the region allowed by the SM fits and LEP

7 Higgs Production Direct production occurs mostly via gluon-gluon fusion Associated production through a virtual W or Z boson provides sensitivity in the region where LHC will have more trouble

8 Higgs Decay In the low mass region we are dominated by the decay into two b quarks In the high mass region the situation changes and at 160 GeV/c 2 the most important decay is in two Ws

9 Higgs strategies search Inclusive cross-section ~1pb Tevatron reached the 1pb sensitivity (WZ,ZZ,Single Top cross sections) Low mass Higgs m h <135 GeV/c 2 dominant decay mode H bb very challenging due to QCD background then WH,ZH production becomes our best chance though associated production cross section ~0.1pb High mass Higgs m H >135GeV/c 2 dominant decay mode H WW

10 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions

Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton

11 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions Event rate /fb -1 B.L.Winer,Moriond QCD, 2004 very hard!

12 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions Higgs Signature Example

13 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions

14 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions

15 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions

16 Higgs search strategy The challenge: Extract Higgs signal from a background 10 orders of magnitude larger We need good signature to trigger on: High p T leptons (e,mu), MET+jets, tau dedicated Lepton Identification Optimized on large W/Z samples B-jet tagging CDF uses secondary vertex and jet probability algorithms. Additional NN flavor separators Background estimation is crucial MC predictions: W/Z+jets,diboson,top, Control regions Advance analysis techniques to separate signal from background NN, Matrix elements, Boosted Decision Trees Careful checks in control regions

17 Higgs Channels at CDF Many channels

18 Higgs Channels at CDF Many channels Today, in particular: CDF channels combination Higgs to tautau (TRIESTE)

19 Low mass: WH lνbb It is the most sensitive low-mass Higgs channel 2.7 fb -1 analyzed Event selection high p T lepton (>20 GeV/c) + 2 b-jets with E T >20GeV Backgrounds W+jets, ttbar, single top, WZ, non-w (QCD) This analysis exploits kinematic variables + Matrix Element info + NN flavor separator

20 Low mass: WH lνbb It is the most sensitive low-mass Higgs channel 2.7 fb -1 analyzed Event selection high p T lepton (>20 GeV/c) + 2 b-jets with E T >20GeV Backgrounds W+jets, ttbar, single top, WZ, non-w (QCD) This analysis exploits kinematic variables + Matrix Element info + NN flavor separator

21 High mass: H WW It is the most sensitive Higgs search at the Tevatron 3.6 fb -1 analyzed Event selection 2 high p T leptons (>20 GeV/c) + Missing E T Backgrounds WW, Drell-Yan, ttbar, single top, WZ, non-w (QCD) This analysis uses Matrix Element info + NN, treating separately final states with 0,1 and >= 2 jets

22 High mass: H WW It is the most sensitive Higgs search at the Tevatron 3.6 fb -1 analyzed Event selection 2 high p T leptons (>20 GeV/c) + Missing E T Backgrounds WW, Drell-Yan, ttbar, single top, WZ, non-w (QCD) This analysis uses Matrix Element info + NN, treating separately final states with 0,1 and >= 2 jets All final states are combined together in a likelihood fit providing limits for m H [110,200]

23 Limits from the CDF Search Channels

24 CDF Combination

Tevatron combination http://www-cdf.fnal.

25 Tevatron combination

26 Trieste direct involvement H tautau search interesting in the low mass region H tautau B.R. is small (~10 %) if compared to H bb, but three signal processes are simultaneously considered: total σ x B.R. is comparable to other Higgs analyses

27 Trieste direct involvement H tautau search Latest official result from CDF 2 fb -1 analyzed Event selection 1 medium p T lepton (>10 GeV/c) + 1 hadronic decaying tau + 2 jets Backgrounds WW, Drell-Yan, ttbar, single top, WZ, non-w (QCD) This analysis uses NN to discriminate signal from main backgrounds

28 Trieste direct involvement H tautau search Latest official result from CDF 2 fb -1 analyzed Event selection 1 medium p T lepton (>10 GeV/c) + 1 hadronic decaying tau + 2 jets Backgrounds WW, Drell-Yan, ttbar, single top, WZ, non-w (QCD) This analysis uses NN to discriminate signal from main backgrounds obs.(exp.) limit/sm σ: 30.5 (24.8) at m H = 115 GeV/c 2

29 Trieste direct involvement H tautau search Now the CDF group in Trieste is working on the update of this analysis doubling the data analyzed refining the identification of the hadronic tau by means of Boost Decision Trees (BDTs) hadronic tau decays appear in the detector as narrow jets (small calorimeter clusters) with low tracks and neutral multiplicity the use of BDTs could exploit all information available and take into account correlation among variables

30 Trieste direct involvement H tautau search Now the CDF group in Trieste is working on the update of this analysis doubling the analyzed data refining the identification of the hadronic tau by means of Boost Decision Trees (BDTs) hadronic tau decays appear in the detector as narrow jets (small calorimeter clusters) with low tracks and neutral multiplicity the use of BDTs could exploit all information available and take into account correlation among variables the work mainly aims at maximizing the efficiency while keeping fake hadronic taus (jets that mimic hadronic taus) at the same level of the standard identification

31 Trieste direct involvement H tautau search Now the CDF group in Trieste is working on the update of this analysis doubling the data analyzed refining the identification of the hadronic tau by means of Boost Decision Trees (BDTs) hadronic tau decays appear in the detector as narrow jets (small calorimeter clusters) with low tracks and neutral multiplicity the use of BDTs could exploit all information available and take into account correlation among variables the work mainly aimed at maximizing the efficiency increase while keeping fake hadronic taus (jets that mimic hadronic taus) at the same level of the standard identification Preliminary results with the new tau ID algorithm based on BDTs are promising Jet fakes are kept under control, and tau efficiency is increased of about 20% w.r.t. standard selection The new algorithm is in the process to be implemented in the search: an increase of ~10-20% is expected

! More than 6 fb -1 on tape About 7 fb -1 by the end of 2009

32 Perspectives With 10 fb -1 CDF could reach SM cross section down to 115 GeV/c 2 This is a GOOD reason to run in 2011!! More than 6 fb -1 on tape About 7 fb -1 by the end of 2009 More than 9 fb -1 by the end of 2010 Up to 12 fb -1 if running in 2011

33 Conclusions The Higgs boson search is in its most exciting era ever The Tevatron experiments have achieved sensitivity to the SM Higgs boson production cross section Trieste is actively involved in the update of the H tautau search

34 Bottom line

36 back-up slides

37 Perspectives

38 D0 combination

39 MSSM Higgs

40 MSSM Higgs

41 MSSM Higgs

42 The way CDF and D0 combined their results? bayesian and modified frequentist approaches used systematics and their correlation between channels and experiments taken into account

43 Electroweak precision measurements

$35% µ τ X h ν τ hadronic leptonic decay hadronic decay B.R. 65% (X h mainly π ±0,small frac.$ of K) 41%, τ h τ h 3%, τ µ τ µ 3%, 6%, τ e τ e τ e τ µ 23%, τ h τ µ 23% τ h τ e in this analysis: τ lep τ had B.R.

of K) 41%, τ h τ h 3%, τ µ τ µ 3%, 6%, τ e τ e τ e τ µ 23%, τ h τ µ 23% τ h τ e in this analysis: τ lep τ had B.R.

44 What about tau lepton? Heavy: Mass = 1.78 GeV/c 2 Short lived: mean lifetime = 291 ps (cτ =87 µm) Decay modes: τ eν τ ν e leptonic τ µν τ ν B.R. 35% µ τ X h ν τ hadronic leptonic decay hadronic decay B.R. 65% (X h mainly π ±0,small frac. of K) 41%, τ h τ h 3%, τ µ τ µ 3%, 6%, τ e τ e τ e τ µ 23%, τ h τ µ 23% τ h τ e in this analysis: τ lep τ had B.R. 46% Hadronic tau decays appear in the detector as narrow jets with low tracks and neutral multiplicity. In CDF a two-stage algorithm is defined: TauFinderModule: look for a small calorimeter cluster associated to tracks and π 0 s Two-cone algorithm: Signal cone around seed track, reconstruct P had (p,e) Isolation annulus for g/q jet veto ID selection: a compromise between efficiency and QCD jet τ fake rate 4

45 New Algorithm results The new algorithm is compared to the standard cut-based selection, mantaining fake rates at a similar level; performances are then evaluated in terms of corresponding MC tau efficiency. jet τ fake rate MC τ had efficiency With a similar fake rate, corresponding efficiency is increased in the plateau region of about 20%. 12

Search for High Mass SM Higgs at the Tevatron

Search for High Mass SM Higgs at the Tevatron Les Rencontres de Physique de la Vallee D'Aoste Mar. 6, 2009 Herbert Greenlee Fermilab for the CDF and D0 Collaborations SM Higgs Boson Direct Limit (LEP)