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ATLAS Sensitivity to Standard Model and SUSY Higgs Bosons

ATLAS Sensitivity to Standard Model and SUSY Higgs Bosons. Stathes Paganis University of Sheffield On Behalf of the ATLAS Collaboration SUSY05, 19-July-2005, Durham UK. Outline. Discovery potential for Standard Model Higgs boson Higgs boson properties

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ATLAS Sensitivity to Standard Model and SUSY Higgs Bosons

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  1. ATLAS Sensitivity to Standard Model and SUSY Higgs Bosons Stathes Paganis University of Sheffield On Behalf of the ATLAS Collaboration SUSY05, 19-July-2005, Durham UK

  2. Outline • Discovery potential for Standard Model Higgs boson • Higgs boson properties • Discovery potential for MSSM Higgs bosons ATLAS Sensitivity to SM and SUSY Higgs

  3. ATLAS @ LHC Muon Detectors EM Calorimeter Inner Tracker Hadronic Calorimeter ATLAS Sensitivity to SM and SUSY Higgs

  4. SM Higgs: ATLAS Discovery Potential ATLAS Sensitivity to SM and SUSY Higgs

  5. SM Higgs xsections and branching ratios BR LEP excluded bb   WW ZZ ATLAS Sensitivity to SM and SUSY Higgs

  6. SM Higgs Discovery Potential (Review) High mass: MH > 180GeV H->ZZ->4lepton Has a narrow peak on top of a low background (pp->ZZ) Intermediate mass: 115 < MH < 180GeV Challenging for MH < 130GeV 2004 ATLAS Sensitivity to SM and SUSY Higgs

  7. 115GeV Higgs: first year (10fb-1) complete detector L=30fb-1 Large K-factor~2 not included Total S/ B : ~ 4.2  Systematic errors included • 3 Channels all around 2s, large backgrounds. • Quite challenging. ATLAS Sensitivity to SM and SUSY Higgs

  8. 115GeV Higgs: Experimental Challenges H -> 2photon - EMCalorimeter response uniformity to ~1% is required. ttH -> WW bb -> blv bjj bb - b-tagging for all 4 b-jets to reduce combinatorics. qqH -> tt qq - Forward jet-tagging needed. - Central jet-veto to reduce background. Common: - Good knowledge of the background 1-10%. - All require low threshold triggers. ATLAS Sensitivity to SM and SUSY Higgs

  9. 130GeV Higgs: first year (10fb-1) complete detector Total S/ B : ~ 6  • H->4l small signal but small background • 3/4 channels with less than 3s • qqH->qqWW counting channel (no clear peak); relies on knowledge of background ATLAS Sensitivity to SM and SUSY Higgs

  10. SM Higgs Summary • For MH>180GeV, discovery should come quickly mainly due to the H->4lepton • For MH<180GeV a few tens of fb-1 will be needed (a few years of low luminosity running) • The region around the LEP limit (115GeV) is the most challenging • All channels present experimental challenges: • Uniformity/Linearity/Calibration of the calorimeters • Missing-Et reconstruction • b-tagging • EM isolation, e/mu efficiencies, tau-ID, ... ATLAS Sensitivity to SM and SUSY Higgs

  11. Higgs Properties ATLAS Sensitivity to SM and SUSY Higgs

  12. Higgs Properties • Higgs Mass • Expect ~0.1% accuracy using H->ZZ->4leptons 300fb-1 and H->gg for MH<400GeV (ATLAS+CMS) • Higgs JCP • Spin from H->ZZ and H->WW. • Parity sensitive to angular correlations in H->ZZ->4lepton. • Needs full luminosity. • Higgs Couplings • Only ratios of couplings (or partial widths) are measured in a fairly model independent way. • Absolute coupling determination requires further theoretical assumptions. • Needs full luminosity. ATLAS Sensitivity to SM and SUSY Higgs

  13. Coupling Ratio determination Assumptions A single JCP=0++ Higgs No extra particles in loops, Only SM particles couple to Higgs boson Taken into account Experimental and theoretical uncertainties for signal and background ATLAS Sensitivity to SM and SUSY Higgs

  14. Absolute couplings after assumptions Duehrssen et al hep-ph/0407190 Assumptions: Upper limit for either a coupling or a total width is required. The couplings to W,Z are not stronger than in the SM ( true for any n-Higgs Doublet Model ) Channels considered: H->ZZ(*)->4l H->gg H->WW->ll+Et,miss H->tt ttH, H->bb ATLAS Sensitivity to SM and SUSY Higgs

  15. MSSM Higgs ATLAS Sensitivity to SM and SUSY Higgs

  16. MSSM Minimal Supersymmetric extension: two Higgs doublets  8 degrees of freedom (5 particles): CP-even : h,H CP-odd: A Charged: H+,H- Couplings to SM particles modified w.r.t. SM. ATLAS Sensitivity to SM and SUSY Higgs

  17. CPConserving Benchmark Scenarios At MA>>MZ or MA~Mh,max and tanb>>1, the heavy bosons degenerate in mass while the h decouples at Mh~130 GeV (decoupling regime of MSSM) Maximum Mh depends on stop mixing Xt Examples: • MHMAX scenariomaximal mh < 135 GeV (Xt ~ sqrt(6)*MS) • Nomixing scenariosmall mh < 116 GeV (Xt = 0) ATLAS Sensitivity to SM and SUSY Higgs

  18. Discovery potential in tanb vs MA plane Is at least 1 Higgs boson observable in the entire parameter space? How many Higgs bosons can be observed? Can the SM be discriminated from extended Higgs sectors? • two expected data volumes 30 fb-1 @ low lumi 300 fb-1 = 30 fb-1@ low lumi. + 270fb-1 @high lumi • discovery = 5 sigma excess using Poissonian statistics • no systematic uncertainties yet LEP tanb exclusion:no exclusion for mt larger ~183 GeV ! ATLAS Sensitivity to SM and SUSY Higgs

  19. H,h Discovery Potential 30fb-1 studied for MH>110GeV at low lumi running almost gurantees discovery of at least one h or H with 30 fb-1 SM like h with 30 fb-1 ttll4 n ATLAS Sensitivity to SM and SUSY Higgs

  20. h Discovery Potential 30fb-1 In Maximal Mixing Scenario: VBF htt covers most of the MSSM plane with 30fb-1 The VBF htt channel is also important for other MSSM scenarios VBF htt Experimental Challenge: Missing Et Reconstruction ATLAS Sensitivity to SM and SUSY Higgs

  21. Overall Discovery Potential: 300 fb-1 • at least one Higgs boson observable for all parameters (true not only for MHMAX) • significant area where only lightest Higgs boson h is observable • can SM be discriminated from extended Higgs sector by parameter determination? 300 fb-1 similar results in other benchmark scenarios VBF channels , H/Att only used with 30fb-1 ATLAS Sensitivity to SM and SUSY Higgs

  22. SM vs MSSM Higgs discrimination • estimate of sensitivity from rate measurements in VBF channels (30fb-1) • compare expected measurement of R in MSSM with prediction from SM BR(h WW) BR(h tt) D=|RMSSM-RSM|/sexp R = 300 fb-1 • only statistical errors • assume Mh exactly known needs further study incl. sys. errors ATLAS Sensitivity to SM and SUSY Higgs

  23. The CP violating CPX scenario • CP conserving at Born level, but CP violation via complex At, Ab Mgl • CP eigenstates h, A, H mix to mass eigenstates H1, H2, H3 • maximise effect  CPX scenario(Carena et al., Phys.Lett B495 155(2000)) • arg(At)=arg(Ab)=arg(Mgluino)=90 degree • scan of Born level parameters: tanb and MH+- ATLAS Sensitivity to SM and SUSY Higgs

  24. CPX Phenomenology • H1,H2,H3 coupling to W,Z • H2,H3 H1H1, ZH1,WW, ZZdecays H1 sum rule: Si gi (ZZHi) = gSM 2 H2 2 H3 • no absolute limit on mass of H1 from LEP • strong dependence of excluded region on value for mtop on calculation used FeynHiggs vs CPH ATLAS Sensitivity to SM and SUSY Higgs

  25. CPX scenario: overall discovery potential 300 fb-1 • FeynHiggs with Mt=175 GeV • OPAL exclusion for Mt=174.3GeV • small uncovered area at low MH+- MH1: < 70 GeV MH2: 105 to 120 GeV MH3: 140 to 180 GeV small masses below 70 GeV not yet studied in ATLAS FeynHiggs and CPSUPERH calculations ATLAS Sensitivity to SM and SUSY Higgs

  26. Not just science fiction ... First Cosmic rays observed by the ATLAS Tile calorimeter in the underground cavern in mid-June Huge effort from ATLAS physicists to understand the detector (calibration, alignment, etc) ATLAS Sensitivity to SM and SUSY Higgs

  27. Summary • SM Higgs should be discovered with a few tens of fb-1 over the full mass range. • Higgs coupling measurement will require full luminosity. Accuracies of 15-50% are expected depending on the channel. • At least one of the MSSM h or H should be discovered with a few tens of fb-1 • Studies of the CPX scenario have started. ATLAS Sensitivity to SM and SUSY Higgs

  28. Backup Slides ATLAS Sensitivity to SM and SUSY Higgs

  29. Absolute couplings after assumptions SM-like Higgs assumptions: Couplings to W and Z as in the SM. No new particles enter the loop for gg decay. ATLAS Sensitivity to SM and SUSY Higgs

  30. 4 CPConserving Benchmark Scenarios Carena et al. , Eur.Phys.J.C26,601(2003) • MHMAX scenariomaximal mh < 133 GeV • Nomixing scenariosmall mh < 116 GeV • Gluophobic scenario • small gh,gluonmh < 119 GeV • Small a scenario •  small ghbb and ghtt mh <123 GeV Affects: VBF, htt tth, hbb Affects gluon fusion channels: gg h, hgg and hZZ4 l ATLAS Sensitivity to SM and SUSY Higgs

  31. MSSM experimental inputs ATLAS Sensitivity to SM and SUSY Higgs

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