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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. Seminar über Teilchenphysik, Universität Heidelberg, May 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 Seminar über Teilchenphysik, Universität Heidelberg, May 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 only become public this Friday. 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 • signature: 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%)) • 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 • 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 • 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. Motivation forSupersymmetryfrom Higgs sector 2 2 DMH2 = a(MSM-MSUSY) • “solves” hierarchy problem: why v=246 GeV << MPl=1019GeV ? • Higgs boson 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 The Origin Of Mass - Exploring the Higgs Sector at the LHC

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. Higgs Physics is golden (J.Lykken 2000) • Thanks for your attention! Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC

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