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. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs2Outline  Discovery potential for Standard Model Higgs boson  Higgs boson properties  Discovery potential for MSSM Higgs bosons

3. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs3 ATLAS @ LHC Inner Tracker EM Calorimeter Hadronic Calorimeter Muon Detectors

4. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs4 SM Higgs: ATLAS Discovery Potential

5. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs5 SM Higgs xsections and branching ratios BR bb  WW ZZ LEP excluded 

6. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs6 SM Higgs Discovery Potential (Review) 2004 High mass: M H > 180GeV H->ZZ->4lepton Has a narrow peak on top of a low background (pp->ZZ) Intermediate mass: 115 < M H < 180GeV Challenging for M H < 130GeV

7. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs7 115GeV Higgs: first year (10fb -1 ) Total S/  B : ~ 4.2  Systematic errors included complete detector H->  ttH->ttbb qqH->qq  S15015~10 B390045~10 S/B0.040.33 S/√B2.42.2~2.7 3 Channels all around 2 , large backgrounds. Quite challenging. Large K-factor~2 not included L=30fb -1

8. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs8 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 ->  qq - Forward jet-tagging needed. - Central jet-veto to reduce background. Common: - Good knowledge of the background 1-10%. - All require low threshold triggers.

9. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs9 130GeV Higgs: first year (10fb -1 ) Total S/  B : ~ 6  complete detector H->4l small signal but small background 3/4 channels with less than 3  qqH->qqWW counting channel (no clear peak); relies on knowledge of background H->  H->4lqqH->qqWWqqH-> qq  S120518~8 B2500<115~6 S/B0.05~1 S/√B2.42.83.92.6

10. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs10 SM Higgs Summary  For M H >180GeV, discovery should come quickly mainly due to the H->4lepton  For M H <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,...

11. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs11 Higgs Properties

12. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs12 Higgs Properties  Higgs Mass Expect ~0.1% accuracy using H->ZZ->4leptons 300fb -1 and H->  for M H <400GeV (ATLAS+CMS)  Higgs J CP 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.

13. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs13 Coupling Ratio determination A single J CP =0 ++ Higgs Assumptions No extra particles in loops, Only SM particles couple to Higgs boson Experimental and theoretical uncertainties for signal and background Taken into account

14. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs14 Absolute couplings after assumptions 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 ) Duehrssen et al hep-ph/0407190 Channels considered: H->ZZ (*) ->4l H-> H->WW->ll+E t,miss H-> ttH, H->bb

15. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs15 MSSM Higgs

16. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs16 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.

17. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs17 CPConserving Benchmark Scenarios  MHMAX scenario maximal m h < 135 GeV (X t ~ sqrt(6)*M S )  Nomixing scenario small m h < 116 GeV (X t = 0) Examples: At M A >>M Z or M A ~M h,max and tan  >>1, the heavy bosons degenerate in mass while the h decouples at M h ~130 GeV (decoupling regime of MSSM) Maximum M h depends on stop mixing Xt

18. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs18 Discovery potential in tan  vs M A plane LEP tan exclusion: no exclusion for m t larger ~183 GeV !  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 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?

19. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs19 H,h Discovery Potential 30fb -1 almost gurantees discovery of at least one h or H with 30 fb -1 studied for M H >110GeV at low lumi running SM like h with 30 fb -1   ll4

20. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs20 h Discovery Potential 30fb -1 In Maximal Mixing Scenario: VBF h  covers most of the MSSM plane with 30fb -1 The VBF h  channel is also important for other MSSM scenarios VBF h   Experimental Challenge: Missing E t Reconstruction

21. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs21  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? similar results in other benchmark scenarios VBF channels, H/A  only used with 30fb -1 300 fb -1 Overall Discovery Potential: 300 fb -1

22. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs22 SM vs MSSM Higgs discrimination BR(h  WW) BR(h  )  estimate of sensitivity from rate measurements in VBF channels (30fb -1 ) R = 300 fb -1  only statistical errors  assume M h exactly known needs further study incl. sys. errors  compare expected measurement of R in MSSM with prediction from SM =|R MSSM -R SM | exp

23. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs23 The CP violating CPX scenario  maximise effect  CPX scenario (Carena et al., Phys.Lett B495 155(2000)) arg(A t )=arg(A b )=arg(M gluino )=90 degree  scan of Born level parameters: tan and M H+-  CP eigenstates h, A, H mix to mass eigenstates H 1, H 2, H 3  CP conserving at Born level, but CP violation via complex A t, A b M gl

24. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs24 CPX Phenomenology  H 1,H 2,H 3 coupling to W,Z H3 H2 H1  H 2,H 3  H 1 H 1, ZH 1, WW, ZZ decays sum rule:  i g i (ZZH i ) = g SM  no absolute limit on mass of H 1 from LEP  strong dependence of excluded region on value for m top on calculation used FeynHiggs vs CPH 2 2

25. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs25 CPX scenario: overall discovery potential M H1 : < 70 GeV M H2 : 105 to 120 GeV M H3 : 140 to 180 GeV small masses below 70 GeV not yet studied in ATLAS  FeynHiggs with M t =175 GeV  OPAL exclusion for M t =174.3GeV  small uncovered area at low M H+- FeynHiggs and CPSUPERH calculations 300 fb -1

26. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs26 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)

27. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs27Summary  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.

28. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs28 Backup Slides

29. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs29 Absolute couplings after assumptions SM-like Higgs assumptions: Couplings to W and Z as in the SM. No new particles enter the loop for  decay.

30. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs30 4 CPConserving Benchmark Scenarios Carena et al., Eur.Phys.J.C26,601(2003 )  Gluophobic scenario small g h,gluon m h < 119 GeV  Small  scenario  small g hbb and g h m h <123 GeV  MHMAX scenario maximal m h < 133 GeV  Nomixing scenario small m h < 116 GeV Affects gluon fusion channels: gg  h, h   and h  ZZ  4 l Affects: VBF, h   tth, h  bb

31. 19-July-2005ATLAS Sensitivity to SM and SUSY Higgs31 MSSM experimental inputs channellumi Mass range Publication VBF, H   WW  low M>110 GeV SN-ATLAS-2003-024 ttH, H  bb low+highM>70GeVATL-PHYS-2003-003 bbH/A   low+high70<M<135GeV M> 120 GeV ATL-PHYS-2002-021ATL-PHYS-2000-005 bbH/A     lep.had,   had.Had lowlowM>120GeV M > 450 GeV ATL-PHYS-2000-001 ATL-PHYS-2003-008 gb  tH+-, H  ,tb low+high M >180 GeV SN-ATLAS-2002-017 tt  bW bH+-, H+-   low M < 170 GeV ATL-PHYS-2003-58 H/A   low+high M > 350 GeV TDR A  Zh  llbb, H  hh   bb low+high 60 <ML<130 100<MH<360 TDR TDR H   low+high M > 70 GeV TDR ZZ  4l low+high M > 100 GeV TDR WW  l l WW  l l low+high 140<M <120GEV TDR WH  l bb low70<M<130GeVTDR