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Higgs Physics at the Large Hadron Collider

Higgs Physics at the Large Hadron Collider. Markus Schumacher, Bonn University. NRW Phenomenology Meeting 2006, Bad Honnef, January 2006. Outline. the Higgs Mechanism and SM Higgs phenomenology at LHC. Higgs physics program at the LHC. discovery of 1 neutral scalar SM like Higgs boson

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Higgs Physics at the Large Hadron Collider

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  1. Higgs Physics at theLarge Hadron Collider Markus Schumacher, Bonn University NRW Phenomenology Meeting 2006, Bad Honnef, January 2006

  2. Outline • the Higgs Mechanism and SM Higgs phenomenology at LHC • Higgs physics program at the LHC • discovery of 1 neutral scalar SM like Higgs boson (determination of mass, spin, CP) • discrimination: SM or extended Higgs sectors (e.g. MSSM) direct observation of additional Higgs bosons determination of Higgs profile: deviations from SM prediction quantum numbers: spin and CP BRs, total width, couplings self coupling at SLHC - > 1 neutral Higgs boson - charged Higgs boson - exotic decays:Hinvisible Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  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 • bad 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 • vacuumspontaneously breaks gauge symmetry • one new particle:the Higgs boson H F =v+H • Higgs boson mass unknown: theory: unitarity  MH<1TeV • LEP search: MH<114.4 GeV electroweak fit: MH<186 GeV excluded at 95% CL at 95%CL Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  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 unknown Higgs mass fixes Higgs profile completely Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  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 at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  6. pp collisions at the Large Hadron Collider LHC SPPS • start in 2007 at ECM of 14 TeV • first years: low lumi running  10 fb-1/year • later (x10): high lumi running  100 fb-1/year Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  7. Complexity of a LHC event hard process + ISR,FSR + underlying event + ~23 additional pp-interactions per bunch crossing at high lumi  ~109 proton-proton collisions / sec  ~1600 charged particles in detector per event Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  8. The challenge of reconstruction low lumi. high lumi. Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  9. Production of the SM Higgs Boson at LHC K = s(N)NLO/sLO K ~ 2 K ~ 1.2 K ~ 1.4 • Ds~4 to 15% + D from PDF (5 to15%) • signal MC at NLO only avaiable for GGF • background: NLO calculations often not avaiable • ATLAS: use K=1 and LO MC for signal and BG • CMS:K-factor for GGF + „guestimated“ K for BG K ~ 1.1 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  10. 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 at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  11. Considerations for Discovery Channels • sufficient signal rate no sensitivity to Hmm in SM • efficient trigger (g,e,m, …) no sensitivity for: GGF, WBF: Hbb • H mass reconstructable?yes: Hgg, ZZ, bb, ttno: HWW • control of background - signal-to-background ratio - estimate of BG from data possible? - sometimes: shape from MC needed • main discovery channels • GGF: H  gg • GGF: H  ZZ  4l+- • GGF: HWW2(ln) • ttH: H  bb • VBF: H  tt • VBF: H  WW ATLAS excluded by LEP since 2000 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  12. H 2 Photons • background: - reducible: pp gj+x, jj+x,..  photon vs. jet seperation - irreducible: ppgg+X  diphoton mass • signal: two photons CMS • mass resolution sM/M = 0.7% - uniformity/understanding of ECAL - dead material: % of unconverted g - pile up: vtx constraint CMS 100fb-1 • background estimate from sidebands •  no Monte Carlo needed • exp. uncertainty: O(0.1%) NLO red./irred. BG: 2 to 1 after final cut LO  NLO: increase of S/ÖB ~ 5060% (K-factor ~ 2, larger Higgs Pt) S/BG ~ 1/10 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  13. H ZZ(*)4 Leptons • signal:4 iso. leptons 1(2) dilepton mass= MZ • reducible BG: tt, Zbb  4 leptons  lepton isolation and veto against b-jets CMS • irreducible BG: ZZ  4 leptons  four lepton mass • good mass resolution sM: <~1%  muon spectrometer + tracking detectors CMS 100fb-1 NLO • small and flat background  easy estimate from sidebands no Monte Carlo needed Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  14. H WW  ln ln • signal: - 2 leptons + missing ET - lepton spin corrleations - no mass peak  transverse mass ATLAS M=160GeV 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 normalisation rom sideband shape from MC • NLO effect on spin corr.  ggWW contribution signal like DFll Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  15. Vector Boson Fusion: ppqqH • signature: • 2 forward jets with large rapidity gap • only Higgs decay products in central part of detector rapidity of tag jets rapidity difference Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  16. Vector Boson Fusion: ppqqH Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  17. Vector Boson Fusion: challenges ATLAS • forward jet reconstruction influence of UE and pile up?  so far only for low lumi pT>20GeV h • central jet veto: influence of UE and pile up? •  so far only for low lumi • efficiency of jet veto at NLO.? • distributions at NLO calculated but: need NLO MC generator for signal and BG Zeppenfeld et al. Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  18. Vector Boson Fusion: H tau tau  ll 4 n (or l had 3 n) • signature:tagging jets +2 high pt leptons + large missing ET • backgrounds:tt,Zjj central jet veto reconstruction of mtt collinear approximation Httem ATLAS 30 fb-1 • expected BG uncertainty ~ 5 to 10% for MH > 125 GeV: flat sideband for MH < 125 normalisation from Z peak, but shape? • mass resolution ~ 10% • dominated bei Emiss resolution Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  19. 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 at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  20. Weak Boson Fusion: HWWllnn (lnqq) VBF versus inclusive channel H2 photons  S/BG ~ 1/1 S/BG ~1/10  CMS ATLAS M=160GeV 30fb-1 ATLAS HWWll  S/BG ~ 4/1 S/BG ~ 2/3  HWWe 10 fb-1 MH=160 GeV • smaller rate larger sig-to-BG ratio smaller K-factor • more challenging for detector understanding • order of significance depends on channel and Higgs mass Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  21. Discovery Potential for light SM Higgs boson excluded by LEP • for GGF: raise of significance by ~ 50% from LO to NLO • results for cut based analysis  improvement by multivariate methods • 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 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  22. 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: i) statistical ii) absolute energy scale 0.1 (0.02) % for l,g,1% for jets iii) 5% on BG + signal for HWW ATLAS VBF with Htt or WW not studied yet ! DM/M: 0.1% to 1% Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  23. Determination of Higgs boson couplings • couplings in production sHx= const x GHxand decay BR(Hyy) = GHy / Gtot prod decay GHX GHy 2 partial width:GHz ~ gHz sHx x BR ~ Gtot • tasks: - disentangle contribution from production and decay • - determine Gtot • model independent: • only ratio or partial decay widths • 13 signal rates used in global fit (incl. various syst. uncertainties) 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 at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  24. Absolute couplings with gV < gVSM constraint • for MH<200 GeV, Gtot<<mass resolution  no direct determination  have to use indirect constraints onGtot • coupling to W, Z, t, b, t Dührssen et al. • lower limit from observable rates: Gtot > GW+GZ+Gt+Gg+.... • upper limit needs input from theory: mild assumption: gV<gVSM rate(VBF,HWW)~GV2/Gtot<(GV2in SM)/Gtot  Gtot< rate/(GV2 in SM) Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  25. Motivation forSupersymmetryfrom Higgs Sector 2 2 DMH2 = a(MSM-MSUSY) • “solves” hierarchy problem: why v=246 GeV << MPl=1019GeV ? • Higgs mass problem in SM: 2 DMH2 = aL2 =aMPlanck W W + H  natural value ~ MPl vs electroweak fit MH~O(100GeV) H • 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 O(5) additional parameters Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  26. 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 corrections: 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 main questions for LHC: • 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? Mtop=174.3 GeV calculated with FeynHiggs Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  27. Light Higgs Boson h 300 fb-1 30 fb-1 ATLAS preliminary ATLAS preliminary • large area covered by many channels  sure discovery and parameter determination possible • small area uncovered @ mh~95 GeV • VBF, Htt covers hole plane from either H or h observation with 30fb-1 • VBF dominates observation • small area from bbh,hmm for small Mh Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  28. 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 • can H SUSY decays or Higgs from SUSY decays provide observation? • discrimination via h profile • determination? ATLAS preliminary similar results in other benchmark scenarios VBF channels , H/Att only used with 30fb-1 Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  29. Higgs Decays to Gauginos e.g. H0 20 20  10 10+4l CMS 100fb-1 dominant background from SUSY Msleptons=250 GeV • results for most optimistic • scenarios shown  fine tuned • require small slepton masses • for large BR(2  1 +2 leptons ) • reduced sensitivity for other channels, • consistent interpretation needed Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  30. 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 • same contribution from GGF D=|RMSSM-RSM|/sexp Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  31. CP-Violating MSSM: Overall Discovery Potential • at Born level: CP symmetry conserved in Higgs sector • complex SUSY parameters  mixing between neutral CP eigenstates • no absolute mass limit from LEP 300 fb-1 • yet uncovered area • size and location of „hole“ depends on Mtop and program for calculation ATLAS preliminary MH1: < 70 GeV MH2: 105 to 120 GeV MH3: 140 to 180 GeV small masses below 70 GeV not yet studied in ATLAS Markus Schumacher Higgs Physics at the LHC NRW-Pheno-06, Bad Honnef, January 2006

  32. 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  see 2nd next talk • 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 at the LHC NRW-Pheno-06, Bad Honnef, January 2006

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