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Higgs Physics with ATLAS

Higgs Physics with ATLAS. Markus Schumacher, Bonn University. MPI Kolloquium, Werner-Heisenberg-Institut, November 29th 2005. Outline. the Higgs Mechanism and SM Higgs phenomenology at LHC discovery potential for SM Higgs boson investigation of the Higgs boson profile

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Higgs Physics with ATLAS

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  1. Higgs Physicswith ATLAS Markus Schumacher, Bonn University MPI Kolloquium, Werner-Heisenberg-Institut, November 29th 2005

  2. Outline • the Higgs Mechanism and SM Higgs phenomenology at LHC • discovery potential for SM Higgs boson • investigation of the Higgs boson profile • phenomenology of SUSY Higgs bosons • discovery potential for MSSM Higgs bosons • discriminating the SM from extended Higgs sectors • conclusion and outlook Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  3. The Higgs Mechanism in the Nut Shell The problem: • consistent description of nature seems to be based on gauge symmetry • SU(2)LxU(1) gauge symmetry  no masses for W and Z and fermions • „ad hoc“ mass terms spoil • renormalisibility  no precise calculation of observables • high energy behaviour  WLWL scattering violates unitarity at ECM~1.2 TeV The „standard“ solution: • new doublet of complex scalar fields • with appropiately choosen potential V • vacuum spontaneously breaks gauge symmetry • one new particle: the Higgs boson H F =v+H Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  4. Mass generation and Higgs couplings: F = v+H x Interaction of particles withv=247 GeV v =247 GeV gf effective mass = friction of particles with omnipresent „Äther“ fermion x x 2 mf ~ gfv Yukawa coupling MV ~ gvgauge coupling g gauge W/Z boson Interaction of particles withHiggs H Higgs gf Fermions gf ~ mf / v W/Z Bosons: gV ~ 2 MV / v fermion v Higgs x 2 g gauge VVH coupling ~ vev only present after EWSB breaking !!! W/Z boson 1 unknown parameter in SM: the mass of the Higgs boson Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  5. Higgs Boson Decays in SM bb WW ZZ tt cc tt gg gg HDECAY: Djouadi, Spira et al. for M<135 GeV: H  bb, tt dominant for M>135 GeV: H  WW, ZZ dominant tiny: H  gg also important Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  6. Status of SM Higgs Searches I: LEP Direct search: MH<114.4 GeV excluded at 95% CL Electroweak fit: MH < 186 GeV at 95% CL ,mtop=172 GeV (MH<216 GeV for mtop=175 GeV) Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  7. Status of SM Higgs Searches II: TEVATRON Expected sensitivity: 95% CL exclusion up to 130 GeV with 4fb-1 per experiment 3 sigma evidence up to 130 GeV with 8fb-1 per experiment Current sensitivity:: Cross section limits at level of ~ 10 x SM cross section Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  8. Higgs Physics at LHC • discovery of 1 neutral scalar Higgs boson (determination of mass, spin, CP) • discrimination between SM and extended Higgs sectors direct observation of additional Higgs bosons determination of Higgs profile: deviations from SM prediction • > 1 neutral Higgs boson • charged Higgs boson • exotic decay modes • e.g. H invisible • 4) … … … • mass • quantum numbers: • spin and CP • BRs, total width, couplings • self coupling at SLHC Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  9. LHC and ATLAS • LHC: proton proton collisions at ECM = 14 TEV, start in 2007 • low luminosity running: 1(2)x1033 /(cm2 s) 10(20) fb-1/year • high luminosity running: 1034/(cm2 s)  100 fb-1/year • AToroidal LHC Aparatus • H2 photons, HZZ 4 leptons • anticipated sM/MH ~ 1 % •  em.-calorimetry, m-spectrometer • ttH, Hbb • eb=60(50)% Rc>10 Rudsg>100 •  Si tracking detectors • Htau tau, WWlnln, VBF prod. • missing E. resolution, hermiticity, • forward jets  calorimetry to h = 5 • MC studies with fast simulation of ATLAS detector • key performance numbers from full sim.: b/tau/jet/el./g/m identification, isolation criteria, jet veto, mass resolutions, trigger efficiencies, … Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  10. Production of the SM Higgs Boson at LHC Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  11. QCD corrections and Knowledge of Cross Sections e.g.: Gluon Gluon Fusion • K = sNNLO/sLO~2 • Ds = 15% from scale variations • error from PDF uncertainty ~10% • Caveat: scale variations may • underestimate the uncertainties! Harlander et al. • ttH: K ~ 1.2 Ds~ 15% WH/ZH: K~1.3 to1.4 Ds~7% • VBF: K ~ 1.1 Ds~ 4% + uncertainties from PDF (5 to 15%) • but: rarely MC at NLO avaiable (except gluon gluon fusion) • background: NLO calculations often not avaiable  need background estimate from data  ATLAS policy: use K=1 for signal Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  12. Cross sections for Background Processes l  q q W W q H p p q l  Background: mainly QCD driven q q q p p q Signal: often electroweak interaction  photons, leptons, … • overwhelming background • trigger: 10-7 reduction on leptons, photons, missing E Higgs 150 GeV: S/B <= 10-10 Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  13. Discovery Potential for light SM Higgs boson excluded by LEP excluded by LEP For MH>330 GeV also: VBF: H  ZZ  llnn VBF: WW  lnqq • discovery channels • GGF: H  gg • GGF: H  ZZ  4l+- • GGF: HWW2(ln) • ttH: H  bb • VBF: H  tt • VBF: H  WW since 2000 For MH>300 GeV also: VBF: H  ZZ  llnn VBF: WW  lnqq • no fully hadronic final states: eg. GGF, VBF: Hbb • Higgs Boson mass reconstruction possible? • background controlable (S/B), estimate from data possible? Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  14. H 2 Photons ATLAS • signature: two highPtg • background: irreducible pp gg+x • reducible ppgj, jj, … • exp issues (mainly for ECAL): • g, jet separation • energy scale, angular resolution • conversions/dead material ATLAS 100fb-1 mass resolution sM: ~1% S/BG ~ 1/20 precise background estimate from sidebands (O(0.1%)) preliminary NLO study: increase of S/ÖB by 50% Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  15. Gluon Fusion: H ZZ(*)4 Leptons • signature: 4 high pt isolated leptons 1(2) dilepton mass ~ MZ • irreducible BG: ZZ  mass reconstruction • reducible BG: tt, Zbb  4 leptons  rejection via lepton isolation and b-veto ATLAS TDR • good mass resolution sM: ~1% • small and flat background  easy estimate from data • preliminary NLO study indicates significance increase by 25% Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  16. Gluon Fusion: H WW  ln ln • signature: - 2 high pt leptons + large missing ET - lepton spin corrleations - no mass peak  transverse mass ATLAS M=170GeV L=30fb-1 transverse mass • BG: WW, WZ, tt • lepton iso., missing E resolution • jet (b-jet) veto against tt Dührssen, prel. • BG estimate in data from DFll • NLO effect on spin corr.  ggWW contribution signal like DFll Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  17. ttH with Hbb • signature: 1 lepton, missing energy 6 jets of which 4 b-tagged • reducible BG: tt+jets, W+jets  b-tagging irreducible BG: ttbb  reconstruct mass peak • exp. issue: full reconstruction of ttH final state  combinatorics !!! need good b-tagging + jet / missing energy performance ATLAS • mass resolution sM: ~ 15% • 50% correct bb pairings • very difficult background estimate from • data with exp. uncertainty ~ O(10%) •  normalisation from side band •  shape from „re-tagged“ ttjj sample 30 fb-1 S/BG ~ 1/6 only channel to see Hbb Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  18. Vector Boson Fusion: ppqqH Higgs Decay Forward tagging jets Jet f h Jet • signature: • 2 forward jets with • large rapidity gap - only Higgs decay products • in central part of detector Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  19. Vector Boson Fusion: ppqqH • 2 forward tagging jets with rapidity gap: • theory questions: • jet distributions at NLO? • esp. direction of 3rd jet? efficieny of central jet veto? • need NLO MC generator for signal and BG h Dh • experimental issues: forward jet reconstruction jet-veto fake rate due to pile up ATLAS ATLAS High Lumi Low Lumi pT>20GeV h Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  20. Weak Boson Fusion: HWWllnn (lnqq) • signature: tagging jets + - 2 high pt leptons + large missing ET - lepton spin corrleations (spin10) - no mass peak  transverse mass • backgrounds: tt, Wt, WWjj, ... central jet veto b-veto ATLAS HWWe • S/BG ~ 3.5/1 • BG uncertainty ~ 10 % shape from MC normalisation from side bands in MT and Dfll 10 fb-1 MH=160 GeV Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  21. Vector Boson Fusion: H tau tau  ll 4 n (l had 3 n) • signature: tagging jets + - 2 high pt leptons + large missing ET - mass reconstruction despite 4 n in collinear approximation • backgrounds: Zjj, tt central jet veto MH=120 GeV Httem reconstruction of mtt • mass resolution ~ 10% determined by missing E. resolution • BG uncertainty ~ 5 to 10% for MH > 125 GeV: flat sideband for MH < 125 normalisation from Z peak ATLAS 30 fb-1 S/BG ~ 1 to 2 / 1 Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  22. Vector Boson Fusion, Htt: estimate of BG shape from data • Idea: jjZmmandjjZttmm • look almost the same, esp. in calos •  same missing energy • only m momenta different • Method: select Z mm events randomise mmomenta apply „normal“ mass reco. promising prel. results from ongoing diploma thesis in BN (M. Schmitz) PTmiss,final (GeV) Mtt (GeV) Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  23. SM discovery potential depending on int. luminosity excluded by LEP • discovery from LEP exclusion until 1 TeV • from combination of search channels with 15 fb-1 of well understood data • with individual search channels with 30 fb-1 of well understood data • for GGF: raise of significance by up to 50% at NLO • results for cut based analysis  improvement by multivariate methods Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  24. Measurement of Higgs Boson Mass • Direct from mass peak: HggHbbHZZ4l • “Indirect” from Likelihood fit to transverse mass spectrum: HWWlnln WHWWWlnlnln • Uncertainties considered: ATLAS i) statistical ii) absolute energy scale 0.1 (0.02) % for l,g,1% for jets iii) 5% on BG + signal for HWW VBF with Htt or WW not studied yet ! DM/M: 0.1% to 1% Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  25. Determination of Higgs boson couplings Born level couplings: Fermions gf = mf / v W/Z Bosons: gV = 2 MV / v x H x 2 Loop induced effective couplings: (sensitive to new physics) Photon: gg = gW “+“ gt “+“… Gluon: gg = gt “+“ gb “+“… • couplings in productionsHx= const x GHx and decay BR(Hyy) = GHy / Gtot • experiment: rate = Nsig+NBG Nsig= L x efficiency x sHx x BR  need to know: luminosity, efficiency, background prod decay GHX GHy 2 partial width:GHz ~ gHz sHx x BR ~ Gtot • tasks: - disentangle contribution from production and decay • - determine Gtot Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  26. Ratio of Partial Widths  • ratios of BRs = ratios of G = ratios of g, if only Born level couplings e.g.  13 analysis used 9 fit parameters: including various exp. and theo. errors all rates can be expressed by those 9 parameters H WW chosen as reference as best measured for MH>120 GeV For 30fb-1 worse by factor 1.5 to 2 Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  27. Total Decay Width GH • for MH>200 GeV, Gtot>1GeV  measurement from peak width in ZZ4 l • for MH<200 GeV, Gtot<< mass resolution  no direct determination  have to use indirect constraints onGtot • lower limit from observable rates: Gtot > GW+GZ+Gt+Gg+.... • upper limit needs input from theory: mild assumption: gV<gVSM valid in models with only Higgs doublets and singlets rate(VBF, HWW) ~ GV2 / Gtot < (GV2 in SM)/ Gtot  Gtot< rate/(GV2 in SM) Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  28. Absolute couplings with gV < gVSM constraint • Ginvfor undetactable decays e.g. c, gluons,new • coupling to W, Z, t, b, t • Gphoton (new), Ggluon (new): non SM contribution to loops Dg/g = ½ D(g2)/g2 Dg/g = ½ D(g2)/g2 Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  29. Motivation forSupersymmetryfrom Higgs Sector 2 2 DMH2 = a(MSM-MSUSY) • “solves” hierarchy problem: why v = 246 GeV << MPl=1019GeV ? • Higgs problem in SM: • large corrections to the mass of the Higgs-Boson W W 2 + DMH2 = aL2 =aMPlanck H H  natural value ~ MPl  electroweak fit MH~O(100GeV) • SUSY solution: • partner with spin difference by ½ cancel divergence exactly if same M • SUSY broken in nature, but hierarchy still fine if MSUSY~1 TeV c+ H H - c- • SUSY breaking in MSSM: • parametrised by 105 additional parameters • too many  constrained MSSM with 5 (6) additional parameters Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  30. The MSSM Higgs sector in a tiny Nut Shell • SUSY: 2 Higgs doublets  5 physical bosons real MSSM: 2 CP even h, H, 1 CP odd A, charged H+, H- • at Born level 2 parameters: tanb, m A mh < MZ • large loop corrections from SUSY breaking parameters mh < 133 GeV for mtop=175 GeV, MSUSY=1TeV • corrections depend on 5 SUSY parameters: Xt, M0 , M2, Mgluino, m fixed in the benchmark scenarios e.g. MHMAX scenario  maximal Mh conservative LEP exclusion • gMSSM = xgSM • no coupling of A to W/Z • small a small BR(htt,bb) • large b large BR(h,H,Att,bb) a = mixing btw. CP-even neutral Higgs bosons Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  31. Discovery Potential in the tanb versus MA Plane main questions for ATLAS: • 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? • LEP tanb exclusion: no exclusion for mt larger ~183 GeV ! • TEVATRON: so far exclusion for tanb > 50, MA<200GeV Mtop=174.3 GeV • calculations with FeynHiggs (Heinemeyer, Hahn, et al.) • no systematic uncertainties yet Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  32. The four CPC Benchmark Scenarios Carena et al. , Eur.Phys.J.C26,601(2003) • MHMAX scenariomaximal mh < 133 GeV  conservative LEP exclusion • Nomixing scenariosmall mh < 116 GeV  difficult for LHC • Gluophobic scenario • small gh,gluon mh < 119 GeV • Small a scenario •  small ghbb and ghtt mh <123 GeV theo. goal: harm discovery via gg h, hgg and hZZ4 l theo. goal: harm discovery via VBF, htt tth, hbb Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  33. Vector Boson Fusion: 30 fb-1 h or H observable with 30 fb-1 studied for MH>110GeV at low lumi running Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  34. Vector Boson Fusion: 4 CPC scenarios almost same conclusion for all 4 CP conserving benchmark scenarios Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  35. Light Higgs Boson h: 30 fb-1 observable channels: VBF bbh hmm tth hbb • difference mainly due to different mh in same (tanb,MA) point ( up to 17 GeV difference) Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  36. Small a scenario, h: 30 fb-1 • hole due to reduced branching ratio for H tt • covered by enhanced BR to gauge bosons • complementarity of search channels almost gurantees observation of h Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  37. Light Higgs Boson h: 300 fb-1 (VBF only 30 fb-1) • also hgg, hZZ4 leptons, tthbb contribute • large area coveredby several channels  sure discovery and parameter determination possible • small area uncovered @ mh = 90 to 100 GeV • hgg sensitive in gluophobic scenario due to Wh, tth production Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  38. Heavy Neutral Higgs Bosons large tanb: bbH/A, H/Att,mm s ~ (tanb)2 low mass<450GeV: tt lep. n nhad.n trigger on lepton ATLAS 30fb-1 large mass > 450GeV: also tt had. nhad. n larger rate, trigger on hard tau jets Eff.(LV1TR)= 80% =95% offline selected events Tau ID: eff(tau)=55% rejection(QCD)=2500 H/A tt Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  39. Charged Higgs Bosons • high mass: mH+-> mtop gbH+-t H+-tn tbqq • low mass: mH+-< mtop • ggtt • ttH+-bW • only low lumi. new: Wqq H+-tn • transition region around mtop needs revised experimental analysis • running bottom quark mass used • Xsec for gbtH+- from T. Plehn‘s program Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  40. Overall Discovery Potential: 300 fb-1 300 fb-1 • at least one Higgs boson observable for all parameters in all CPC benchmark scenarios • significant area where only lightest Higgs boson h is observable • questions for future studies: • can SUSY decay modes • provide observation? • e.g.: H/Ac2c22 LSP + 4 lept. • ongoing study in BN (N. Möser) similar results in other benchmark scenarios VBF channels , H/Att only used with 30fb-1 Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  41. SM or Extended Higgs Sector e.g. Minimal SUSY ? discrimination via rates from VBF compare expected measurement of R in MSSM with prediction from SM for same value of MH BR(h WW) BR(h tt) R = 300 fb-1 ATLAS prel. • assume Higgs mass well measured • no systematic errors considered D=|RMSSM-RSM|/sexp Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  42. The Higgs Sector in the CP Violating MSSM • at Born level: CP symmetry conserved in Higgs sector • complex SUSY breaking parameters (m,At) introduce new CP phases  mixing between neutral CP eigenstates mass eigenstates H1, H2, H3 <> CP eigenstates h,A,H Why consider such scenarios? • no a priori reason for real SUSY parameters • baryogenesis: 3 Sacharov conditions B violation: via sphaleron processes CP violation : SM too less, CPV MSSM new sources  fine No therm. Equ. : SM no strong 1st order electroweak phase transition CPV MSSM still fine (even better NMSSM) • evade dipole moments via spurious cancellations or split SUSY Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  43. Phenomenology in the CPX scenario • 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+- • H1,H2, H3 couple to W,Z  all produced in VBF H1 H2 • H2,H3 H1H1, ZH1,WW, ZZ decays possible H3 • no limit for mass of H1 from LEP (compare CPC MSSM: Mh>MZ) LHWG-Note 2005-01 Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  44. CP-Violating MSSM: Overall Discovery Potential 300 fb-1 • yet uncovered area • size and location of „hole“ depends on Mtop and program for calculation MH1: < 70 GeV MH2: 105 to 120 GeV MH3: 140 to 180 GeV small masses below 70 GeV not yet studied in ATLAS • most promising channel: tt bW bH+, H+W H1, H1bb final state: 4b 2j l n same as ttH, Hbb (study in Bonn) • revised studies for H2/3H1H1 also interesting Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  45. Very first look at new promising MC study • t tH+ b W b H+W H1 H1bb • 1 leptonic W decay  lepton for trigger • reconstruct top quarks  combinatorics • associate b quarks to H1, H+  MH1 and M H+ M H+ =135 GeV, MH1=54GeV, tanb=4.8(diploma thesis M. Lehmacher, BN) signal ttjj ttbb • estimate of background seems difficults • coverage of hole area under study! Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  46. Conclusion and Outlook • Standard model: discovery of SM Higgs boson with 15 fb-1 • requires good understanding of whole detector • multiple channels with larger luminosity  Higgs profile investigaton • CP conserving MSSM: at least one Higgs boson observable • only h observable in wedge area at intermediate tanb • maybe Higgs to SUSY or SUSY to Higgs observable? • discrimination via Higgs parameter determination seems promising • CP violating MSSM: probably a „hole“ with current MC studies • promising MC studies on the way • more realistic MC studies: • influence of miscalibrated and misaligned detector • improved methods for background estimation from data • use of NLO calcluations and MCs for signal and background • additional extended models + seach channels: • CPV MSSM, NMSSM, 2HDM • Higgs  SUSY, SUSYHiggs • VBF, Hbb (b-trigger at LV2), VBF,Hinv. (add. forward jet trigger) Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

  47. Let‘s wait and work for Higgs boson discovery …. • Thanks for your attention! Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

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