higgs physics with atlas

Higgs Physicswith ATLAS Markus Schumacher, Bonn UniversityMPI Kolloquium, Werner-Heisenberg-Institut, November 29th 2005

Markus Schumacher Higgs Physics with ATLAS Munich, November 29th 2005

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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


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The Higgs Mechanism in the Nut Shell 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 The problem:The standard solution: new doublet of complex scalar fieldswith appropiately choosen potential V vacuum spontaneously breaks gauge symmetry one new particle: the Higgs boson H F = v + H renormalisibility no precise calculation of observables high energy behaviour WLWL scattering violates unitarity at ECM~1.2 TeV


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Mass generation and Higgs couplings: F = v + H effective mass = friction of particles with omnipresent ther v =247 GeVxfermiongfmf ~ gf v Yukawa coupling MV ~ g v gauge couplingxxW/Z bosong gaugeInteraction of particles with v=247 GeVFermions gf ~ mf / vW/Z Bosons: gV ~ 2 MV / vInteraction of particles with Higgs HfermiongfxW/Z bosong gaugeHiggsHiggsv22VVH coupling ~ vev only present after EWSB breaking !!!1 unknown parameter in SM: the mass of the Higgs boson


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Higgs Boson Decays in SMfor M135 GeV: H WW, ZZ dominant tiny: H gg also importantHDECAY: Djouadi, Spira et al.


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Status of SM Higgs Searches I: LEP MH < 186 GeV at 95% CL ,mtop=172 GeV

(MH10 Rudsg>100 Si tracking detectors Htau tau, WWlnln, 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,


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Production of the SM Higgs Boson at LHC


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QCD corrections and Knowledge of Cross Sections K = s NNLO/sLO~2 Ds = 15% from scale variations error from PDF uncertainty ~10%

Caveat: scale variations may underestimate the uncertainties!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 signale.g.: Gluon Gluon FusionHarlander et al.


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Cross sections for Background ProcessesHiggs 150 GeV: S/B 300 GeV also:VBF: H ZZ llnnVBF: WW lnqq no fully hadronic final states: eg. GGF, VBF: Hbb Higgs Boson mass reconstruction possible? background controlable (S/B), estimate from data possible?since 2000


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H 2 Photons signature: two high Pt g background: irreducible pp gg +x reducible ppgj, jj, exp issues (mainly for ECAL): g, jet separation energy scale, angular resolution conversions/dead materialmass resolution sM: ~1%precise background estimate from sidebands (O(0.1%))S/BG ~ 1/20ATLAS 100fb-1preliminary NLO study:increase of S/B by 50%


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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-vetoATLAS TDR good mass resolution sM: ~1% small and flat background easy estimate from data

preliminary NLO study indicates significance increase by 25%


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Gluon Fusion: H WW ln lnATLASM=170GeVL=30fb-1 signature: - 2 high pt leptons + large missing ET - lepton spin corrleations

- no mass peak transverse masstransverse mass BG: WW, WZ, tt lepton iso., missing E resolution jet (b-jet) veto against tt BG estimate in data from DFll NLO effect on spin corr. ggWW contribution signal likeDhrssen, prel.DFll


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ttH with Hbb 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 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 S/BG ~ 1/630 fb-1only channel to see HbbATLAS signature: 1 lepton, missing energy 6 jets of which 4 b-tagged


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Vector Boson Fusion: ppqqH signature:2 forward jets with large rapidity gap- only Higgs decay products in central part of detector


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Vector Boson Fusion: ppqqH2 forward tagging jets with rapidity gap:pT>20GeVforward jet reconstructionATLASHigh LumiLow Lumijet-veto fake rate due to pile upATLAStheory questions: jet distributions at NLO? esp. direction of 3rd jet? efficieny of central jet veto?need NLO MC generator for signal and BGexperimental issues:hDhh


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signature: tagging jets + - 2 high pt leptons + large missing ET - lepton spin corrleations (spin10) - no mass peak transverse massWeak Boson Fusion: HWWllnn (lnqq)tt, Wt, WWjj, ... backgrounds:HWWeATLAS10 fb-1MH=160 GeV S/BG ~ 3.5/1 BG uncertainty ~ 10 % shape from MC normalisation from side bands in MT and Dfllcentral jet vetob-veto


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ATLASHttemVector Boson Fusion: H tau tau ll 4 n (l had 3 n)

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 peak30 fb-1MH=120 GeV signature: tagging jets + - 2 high pt leptons + large missing ET - mass reconstruction despite 4 n in collinear approximation backgrounds: Zjj, ttS/BG ~ 1 to 2 / 1central jet vetoreconstructionof mtt


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Vector Boson Fusion, Htt: estimate of BG shape from dataIdea: jjZmm and jjZttmmlook almost the same, esp. in calos same missing energy only m momenta differentMethod: select Z mm events randomise m momenta apply normal mass reco.PTmiss,final (GeV)Mtt (GeV)promising prel. results from ongoing diploma thesis in BN (M. Schmitz)


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SM discovery potential depending on int. luminosity excluded by LEPdiscovery from LEP exclusion until 1 TeV from combination of search channels with 15 fb-1 of well understood datawith 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


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Measurement of Higgs Boson MassATLASDM/M: 0.1% to 1% Uncertainties considered:Indirect from Likelihood fit to transverse mass spectrum: HWWlnln WHWWWlnlnlnDirect from mass peak: Hgg Hbb HZZ4lVBF with Htt or WW not studied yet ! i) statistical ii) absolute energy scale 0.1 (0.02) % for l,g ,1% for jetsiii) 5% on BG + signal for HWW


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Determination of Higgs boson couplingsLoop induced effective couplings:(sensitive to new physics)

Photon: gg = gW + gt +

Gluon: gg = gt + gb +HxxBorn level couplings:Fermions gf = mf / vW/Z Bosons: gV = 2 MV / v2 couplings in production sHx= const x GHx and decay BR(Hyy) = GHy / Gtot experiment: rate = Nsig+NBG Nsig= L x efficiency x sHx x BR need to know: luminosity, efficiency, backgroundsHx x BR ~ GHX GHyGtotprod decaypartial width: GHz ~ gHz2 tasks: - disentangle contribution from production and decay - determine Gtot


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Ratio of Partial Widths ratios of BRs = ratios of G = ratios of g, if only Born level couplingse.g.9 fit parameters:all rates can be expressed by those 9 parametersH WW chosen as reference as best measured for MH>120 GeVFor 30fb-1 worse by factor 1.5 to 213 analysis usedincluding various exp. and theo. errors


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Total Decay Width GH for MH>200 GeV, Gtot>1GeV measurement from peak width in ZZ4 l upper limit needs input from theory: mild assumption: gV GW+GZ+Gt+Gg+....for MH

higgs physics with atlas

Documents

higgs mechanism

higgs couplings

sm higgs phenomenology

higgs boson decays

higgs boson h f

mssm higgs bosons

sm higgs boson investigation

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