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The Origin of Mass - Exploring the Higgs Sector at the Large Hadron Collider with ATLAS

The Origin of Mass - Exploring the Higgs Sector at the Large Hadron Collider with ATLAS. Markus Schumacher, Universität Bonn. Particle Physics Seminar, HU Berlin/DESY Zeuthen, 9th June 2006. Outline. Which mass? Why? The mass problem and the SM solution.

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The Origin of Mass - Exploring the Higgs Sector at the Large Hadron Collider with ATLAS

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  1. The Origin of Mass-Exploring the Higgs Sector at the Large Hadron Collider with ATLAS Markus Schumacher, Universität Bonn Particle Physics Seminar, HU Berlin/DESY Zeuthen, 9th June 2006

  2. Outline • Which mass? Why? The mass problem and the SM solution. • Higgs boson phenomenology and experimental environment • Discovery potential for a SM like Higgs boson • Investigation of the Higgs boson profile • Discovery potential for MSSM Higgs bosons • Conclusions • only ATLAS results. CMS TDR will become public very soon. Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  3. Which mass? The nucleon mass 100% Unknown Form of Dark Energy 80% 60% O(%) due to Mu~5 MeV and Md ~10 MeV Rest: kinetic energy of partons + other QCD effects 40% Unknown Form of Dark Matter 20% 0% protons/neutrons in stars, dust,etc. neutrinos Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  4. Particle masses and their relevance • electron mass: def. length scale of our world, Bohr radius a=1/aem me me = 0 no atomic binding me = 0.02MeV human giants 45 m, visible light in infrared me = 105 MeV nucleon capture penn energetically possible  only helium, n + n  different universe • no/small W mass: fusion in stars: p+pD e+n GF~ (MW )-2 short burning time of sun at lower temperature  no humans on earth • quarks massless or mu=md proton mass > neutron mass proton decay pnen possible modified nucleosynthesis  different universe mass values of e, u, d, W and their fine tuning are • essential for creation and development of our universe • principle of mass generation  Higgs mechanism • origin of mass values  even no theoretical explanation yet Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  5. Gauge symmetries of the SM and particele masses • consistent description of nature based on gauge symmetries • electroweak SU(2)LxU(1)Y symmetry forbids „ad hoc“ masses for gauge bosons: W and Z fermions: (l = doublet, r = singlet) • „ad hoc“ mass terms destroy • renormalisibility  no precision prediction for observables • high energy behaviour of theory  e.g. WLWL scattering Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  6. High energy behaviour of s in WWWW violates unitarity at ECM ~ 1.2 TeV massive gauge bosons: 1 longitudinal + 2 transverse d.o.f. massless gauge bosons: only 2 transverse d.o.f. scalar boson H restores unitarity, if gHWW ~ MW gHff ~ Mf and MH < 1TeV s  const=f(MH) Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  7. The Higgs Kibble mechanism The „standard“ solution: one new doublet of complex scalar fields (4 degrees of freedom) with appropriately chosen potential V V = -m2 |f+f| + l |f+f|2 m2,l > 0 minimum of V not at f=0  spontaneous symmetry breaking 3 massless excitations along valley 3 longitudinal d.o.f for W+- and Z 1 massive exciation out of valley  1 d.o.f for „physical“ Higgs boson Higgs field has two „components“ 1) omnipresent, constant background condensate v= 247 GeV (from GF) 2) Higgs boson H with unknown mass MH ~ m ~ Ölv Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  8. Mass generation and Higgs Boson couplings: F = v+H x v =247 GeV gf • interaction with „ether“ v=247 GeV MV~ gvgauge coupling mf~ gfv Yukawa coupling introduced „ad hoc“ Fermion x x 2 g gauge W/Z boson • interaction with Higgs boson H Higgs gf fermions: gf ~ mf / v W/Z bosons: gV ~ MV / v = g2 v 2 fermion v Higgs VVH coupling ~ vev only existent after EWSB  hint towards background condensate x 2 g gauge W/Z boson 1 unknown parameter in SM: MH Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  9. Decays of the Higgs boson in the 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 The Origin Of Mass - Exploring the Higgs Sector at the LHC

  10. What is the mass of the Higgs boson ? • theory: unitarity in WW scattering  MH < 1 TeV • direct search at LEP: MH<114.4 GeV excluded with 95% CL • indirect prediction in SM, e.g. MW(Phys) = MW(Born) + t H W W W W S. Roth b W 2 … mt + … ln(MH) MH < 186 GeV (mtop=172.7 GeV) with 95% CL Standard Model prefers a light Higgs boson Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  11. Status of SM Higgs boson searches at 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 ~ 5 to 20 x SM cross section Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  12. The Large Hadron Collider LHC proton proton collisions at ECM of 14 TeV, start in 2007 initial luminosity: (2)x1033 cm-2s-1 10 to 20 fb-1/year design luminosity: 1034 cm-2s-1 100 fb-1/year Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  13. AToroidal LHC ApparatuS • 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 The Origin Of Mass - Exploring the Higgs Sector at the LHC

  14. Production of the SM Higgs Boson at LHC • gluon fusion dominant for all masses • VBF roughly one order of magnitude smaller • HW, HZ,H tt only relevant for small MH Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  15. 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 Ds~7% VBF: K ~ 1.1, Ds~4% • 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 and background • remark: NLO calculation for total cross section is not NLO calculation for additional jet  needs NNLO or NLO+(N)LL Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  16. Cross sections for background processes overwhelming background: mainly QCD driven signal: often electroweak interaction  photons, leptons, … in final state 3 level trigger system on leptons, photons, missing energy provides reduction by 10 000 000 no access to fully hadronic events e.g. GGF, VBF with Hbb Higgs 150 GeV: S/B <= 10-10 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  17. An event at the LHC „hard“ collision + ISR,FSR + „underlying event“ • + ~23 overlayed pp interactions per bunch crossing at high luminosity •  ~109 proton proton collisions / second • ~1600 charged particles enter detector per event + effects from „pile up“: read out time > Dt btw. bunch crossings Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  18. The challenge of event reconstruction low lumiosity high luminosity Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  19. Which channels may provide discovery? • efficient trigger  no hadronic final states: e.g. GGF, VBF: Hbb • Higgs boson mass reconstructable? which mass resolution? • background reducible and controllable? - good signal-to-background ratio - small uncertainty on BG, estimation from data itself possible? Status 2001 • discovery channels: inclusive: H  2 photons  ZZ  4 leptons  WW  lnln • exclusive: • ttH, Hbb VBF, HZZ,WW for large M Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  20. H 2 Photons • signal: two highPtphotons • background: irreducible pp  gg+x reducible pp  gj, jj, … • exp. issues (mainly for ECAL): • - g, jet separation (Eff=80%, Reject. ~ few 1000) • - energy scale, angular resolution • conversions/dead material ATLAS 100fb-1 • mass resolution sM: ~1 to 1.5% S/BG ~ 1/20 • precise background estimate • from sidebands (O(0.1%)) •  no MC needed • preliminary NLO study: • increase of S/ÖB by 50% Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  21. 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 • irreducible BG: ZZ  4 leptons  four lepton mass • good mass resolution sM~1%  muon spectrometer + tracking detectors • small and flat background  easy estimate from sidebands  no Monte Carlo needed • preliminary NLO study indicates significance increase by 25% Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  22. H  WW  ln ln • signal: - 2 leptons + missing ET - lepton spin corrleations - no mass peak  transverse mass ATLAS M=170GeV 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 : 5% normalisation from sideband shape from MC • NLO effect on spin corr.  ggWW contribution signal like DFll Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  23. ttH with Hbb • signal: 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 • 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 The Origin Of Mass - Exploring the Higgs Sector at the LHC

  24. Vektor boson fusion VBF: ppqqH Jet Jet Forward tagging jets • signature: • 2 forward jets with large rapidity gap • only Higgs decays in central part of dector f h Higgs Decay =-ln tan(q/2) ATLAS ATLAS Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  25. VBF: Challenges ATLAS • reconstruction of taggings jets influence of - „underlying event“ (UE) ? - overlapping events (OE) ? - „pile up“ (PU) ?  so far only low lumi considered pT>20GeV • central jet veto: influence of UE, OE, PU? • efficiency of jet veto at NLO? but: no NLO MC-Generator yet now: study started using SHERPA Zeppenfeld et al. Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  26. VBF: H tt  ll 4 n • signature:tagging jets +2 leptons + large missing tranvsere energy • background:QCD processes tt,Zjj  Dh, central jet veto  reconstruction of mtt collinear approximation Httem ATLAS 30 fb-1 • expected DBG ~ 5 to 10% for MH > 125 GeV: side band for MH < 125 normalisation from Z-peak, shape from Zmm • sM /M ~ 10% • dominated by Emiss Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  27. VBF, Htt: determination of background from data • Idea:jjZmmandjjZttmmwith identical topology • muons are MIPS  same energy deposition in calorimeters • only difference: momentum spectra of muons • Method:select Z  mm events „randomise“ m-momenta according to Z  tt  mm4n MC apply „usual“ selection and mass reconstruction shape of background can be extracted precisely from data itself (M. Schmitz, Diplomarbeit BN 2006) Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  28. Weak Boson Fusion: HWWllnn (lnqq) HWWlnln: VBF versus inclusive channel ATLAS M=170GeV 30fb-1 ATLAS 10 fb-1 HWWe S/BG ~ 3.6 Signal = 82.4 S/BG ~ 0.7 Signal = 144 VBF with respect to gluon fusion • 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 The Origin Of Mass - Exploring the Higgs Sector at the LHC

  29. Discovery potential in SM excluded by LEP 10 fb-1 30 fb-1 excluded by LEP • VBF dominates discovery potential for low mass (at least at LO) • with 15 fb-1 and combination of channels: discovery from LEP to 1TeV • prel. NLO studies: increase of signifcance up to 50% for incl. channels • so far: cut based  improvement with multivariate techniques Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  30. Measurement of Higgs boson mass • Direct from mass peak: HggHbbHZZ4l (energy scale 0.1 (0.02)% for l,g,1% for jets) ATLAS • “Indirect” from transverse mass spectrum: HWWlnln WHWWWlnlnln S. Roth 300 fb-1 DM/M: 0.1% to 1% • Higgs boson mass • determines Higgs sector in the SM • is precision observable of the SM Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  31. Determination of Higgs boson couplings • coupling 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 • goal: - disentangle contribution from production and decay • - determine total width Gtot • model independent: • only ratio of partial width • 13 final states in global fit (including various syst. uncertainties) H WW used as reference as most precise determination for MH>120 GeV Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  32. Absolute Couplings with gV < gVSM • for MH<200 GeV, Gtot<< mass resolution  no direct determination  indirect limits needed 300 fb-1 • coupling to W, Z, t, b, t Dührssen et al. • lower bounds from observed rates: Gtot > GW+GZ+Gt+Gg+.... • upper bound with theoretical input weak assumption: gV<gVSM (true in all models with only doublets and singlets)  Gtot< Rate(VBF,HWW)/(GV2 in SM) Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  33. The Higgs sector of the MSSM • SUSY “solves” hierarchy problem: why MH, v << MPl=1019GeV ? • SUSY needs two Higgs doublets  2 vevs: v1,v2  5 Higgs bosons: h,H,A,H+,H- • 2 parameters determine Higg sector at Born level: tanb=v2/v1, MA + ~100 additional, which are fixed in benchmark scenarios • lightest Higgs boson: Mh<135 GeV (for mtop=175GeV) • modified couplings w.r.t. SM • Is at least one Higgs boson observable at LHC? • Discrimination SM MSSM ? - several Higgs bosons observable - characteristics of h differ from SM Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  34. Discovery potential for light Higgs boson h 300 fb-1 30 fb-1 ATLAS preliminary ATLAS preliminary • large area covered by many channels  stable discovery and parameter determination possible • small area uncovered @ mh~95 GeV • VBF, Htt covers whole plane via observation of h or H with 30fb-1 • VBF dominates observation • small area from bbh,hmm for small Mh Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  35. 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 The Origin Of Mass - Exploring the Higgs Sector at the LHC

  36. SM or extended Higgs Sector e.g. Minimale SUSY ? discrimination via VBF comparison of expected determination of R in MSSM with SM prediction for same MH BR(h WW) BR(h tt) R = 300 fb-1 ATLAS prel. • assumption: Mh well known • no systematic uncertainties D=|RMSSM-RSM|/sexp D=|RMSSM-RSM|/sexp Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  37. 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) • no absolute limit on mass of H1 from LEP Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  38. Discovery potential in CP violating MSSM MH1: < 50 GeV, MH2: 105 to 115 GeV, MH3: 140 to 180 GeV, M H+-:130 to 170 GeV • most promising channel: tt bW bH+, H+W H1, H1bb final state: 4b 2j l n same as ttH, Hbb • revised studies for H2/3H1H1 also interesting Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  39. Conclusions • our universe needs masses of elementary particles • Higgs Kibble mechanism allows their consistent description • LHC: - discovery of Higgs boson in SM with 15fb-1 well understood data • - determination of mass, width, spin, CP • - ratio of partial width, absolute couplings only with theo. input • - CPC MSSM: at least one Higgs boson observable • discrimination from SM seems promising • - CPV MSSM: so far uncovered area at low MH as not studied yet • promising channels are investigated now • now: prepare for data taking • - determine background, trigger eff., id eff./rejection from data • - improve reconstruction and MC simulation (mis. calibration, allignment) • - perform NLO studies and investigate other „exotic“ scenarios Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  40. Higgs Physics is golden (J.Lykken 2000) Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

  41. The new „Weltmeisterformel“ ??? 54 x 74 – 1990 = ??? • Thanks for your attention! Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

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