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

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

4. 4 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Particle masses and their relevance  electron mass: def. length scale of our world, Bohr radius a=1/ em m e m e = 0 no atomic binding m e = 0.02MeV human giants 45 m, visible light in infrared m e = 105 MeV nucleon capture pe  n energetically possible  only helium, n +   different universe  no/small W mass: fusion in stars: p+p  D e+ G F ~ (M W ) -2 short burning time of sun at lower temperature  no humans on earth 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  quarks massless or m u =m d  proton mass > neutron mass proton decay p  nepossible modified nucleosynthesis  different universe

5. 5 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Gauge symmetries of the SM and particele masses  consistent description of nature based on gauge symmetries  electroweak SU(2) L xU(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. W L W L scattering

6. 6 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC High energy behaviour of in WW  WW violates unitarity at E CM ~ 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 g HWW ~ M W g Hff ~ M f and M H < 1TeV   const=f(M H )

7. 7 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC The Higgs Kibble mechanism The „standard“ solution: one new doublet of complex scalar fields (4 degrees of freedom) with appropriately chosen potential V V = - 2 |  | + |  | 2  2, > 0 minimum of V not at =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 G F ) 2) Higgs boson H with unknown mass M H ~  ~ v

8. 8 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Mass generation and Higgs Boson couplings: = v + H v =247 GeV x Fermion gfgf M V ~ g v gauge coupling m f ~ g f v Yukawa coupling introduced „ad hoc“ x x W/Z boson g gauge  interaction with „ether“ v=247 GeV fermions: g f ~ m f / v W/Z bosons: g V ~ M V / v = g 2 v  interaction with Higgs boson H fermion gfgf x W/Z boson g gauge Higgs v 2 2 VVH coupling ~ vev only existent after EWSB  hint towards background condensate 1 unknown parameter in SM: M H 2

9. 9 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC bW ZZ tt  cc gg  Decays of the Higgs boson in the SM for M<135 GeV: H  bb, dominant for M>135 GeV: H  WW, ZZ dominant tiny: H  also important HDECAY: Djouadi, Spira et al.

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

11. 11 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 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

12. 12 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC The Large Hadron Collider LHC proton proton collisions at E CM of 14 TeV, start in 2007 initial luminosity: (2)x10 33 cm -2 s -1  10 to 20 fb-1/year design luminosity: 10 34 cm -2 s -1  100 fb-1/year

13. 13 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC A Toroidal LHC ApparatuS  MC studies with fast simulation of ATLAS detector  key performance numbers from full sim.: b/tau/jet/el.// identification, isolation criteria, jet veto, mass resolutions, trigger efficiencies, …

14. 14 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 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 M H

15. 15 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC QCD corrections and knowledge of cross sections  K =  NNLO / LO ~2   = 15% from scale variations  error from PDF uncertainty ~10% caveat: scale variations may underestimate the uncertainties! ttH: K ~ 1.2, ~15% WH/ZH: K~1.3 ~7% VBF: K ~ 1.1,  ~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 e.g.: gluon gluon fusion Harlander et al.

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

17. 17 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC An event at the LHC + ~23 overlayed pp interactions per bunch crossing at high luminosity  ~10 9 proton proton collisions / second  ~1600 charged particles enter detector per event + effects from „pile up“: read out time > t btw. bunch crossings „hard“ collision + ISR,FSR + „underlying event“

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

19. 19 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Which channels may provide discovery? Status 2001  discovery channels: inclusive: H  2 photons  ZZ  4 leptons  WW  ll exclusive:  ttH, H  bb VBF, H  ZZ,WW for large M  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?

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

21. 21 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC H  ZZ (*)  4 leptons  reducible BG: tt, Zbb  4 leptons  lepton isolation and veto against b-jets  good mass resolution  M ~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%  signal: 4 iso. leptons 1(2) dilepton mass = M Z  irreducible BG: ZZ  4 leptons  four lepton mass

22. 22 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC  signal: - 2 leptons + missing E T - lepton spin corrleations - no mass peak  transverse mass H  WW  l l ATLAS M=170GeV 30fb -1 transverse mass  BG: WW, WZ, tt lepton iso., missing E resolution jet (b-jet) veto against tt  BG estimate in data from  ll : 5% normalisation from sideband shape from MC  NLO effect on spin corr.  gg  WW contribution signal like Dührssen, prel.  ll

23. 23 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC ttH with H  bb  mass resolution  M : ~ 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  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 ~ 1/6 30 fb -1 only channel to see H  bb ATLAS  signal: 1 lepton, missing energy 6 jets of which 4 b-tagged

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

25. 25 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC VBF: Challenges p T >20GeV  reconstruction of taggings jets influence of - „underlying event“ (UE) ? - overlapping events (OE) ? - „pile up“ (PU) ?  so far only low lumi considered ATLAS  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.

26. 26 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC VBF: H    ll 4  signature: tagging jets + 2 leptons + large missing tranvsere energy  background: QCD processes tt,Zjj  central jet veto  reconstruction of m    M /M ~ 10%  dominated by E miss H    e  ATLAS 30 fb -1  expected BG ~ 5 to 10% for M H > 125 GeV: side band for M H < 125 normalisation from Z-peak, shape from Z   collinear approximation

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

28. 28 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Weak Boson Fusion: H  WW  ll (lqq) H  WW  e ATLAS 10 fb -1 H  WW  ll: VBF versus inclusive channel ATLAS M=170GeV 30fb -1 S/BG ~ 3.6 Signal = 82.4 S/BG ~ 0.7 Signal = 144  smaller rate larger sig-to-BG ratio smaller K-factor  more challenging for detector understanding  order of significance depends on channel and Higgs mass VBF with respect to gluon fusion

29. 29 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC excluded by LEP Discovery potential in SM 10 fb -1  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 30 fb -1 excluded by LEP

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

31. 31 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Determination of Higgs boson couplings  coupling in production  Hx = const x  Hx and decay BR(H  yy)=  Hy /  tot  Hx x BR ~  HX  Hy  tot Prod. Decay Partial width:  Hz ~ g Hz 2  goal: - disentangle contribution from production and decay - determine total width  tot H  WW used as reference as most precise determination for M H >120 GeV  model independent: only ratio of partial width  13 final states in global fit (including various syst. uncertainties)

32. 32 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC  for M H <200 GeV,  tot << mass resolution  no direct determination  indirect limits needed Absolute Couplings with g V < g V SM  coupling to W, Z, , b, t Dührssen et al.  lower bounds from observed rates:  tot >  W + Z + t + g +....  upper bound with theoretical input weak assumption: g V <g V SM (true in all models with only doublets and singlets)   tot < Rate(VBF,H  WW)/( V 2 in SM) 300 fb -1

33. 33 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC The Higgs sector of the MSSM  SUSY needs two Higgs doublets  2 vevs: v 1,v 2  5 Higgs bosons: h,H,A,H +,H -  SUSY “solves” hierarchy problem: why M H, v << M Pl =10 19 GeV ?  2 parameters determine Higg sector at Born level: tanv 2 /v 1, M A + ~100 additional, which are fixed in benchmark scenarios  lightest Higgs boson: M h <135 GeV (for m top =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

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

35. 35 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Overall discovery potential: 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? similar results in other benchmark scenarios VBF channels, H/A  only used with 30fb -1 300 fb -1 ATLAS preliminary

36. 36 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC ATLAS prel. 300 fb -1 SM or extended Higgs Sector e.g. Minimale SUSY ? discrimination via VBF R = BR(h  WW) BR(h  )  assumption: M h well known  no systematic uncertainties comparison of expected determination of R in MSSM with SM prediction for same M H =|R MSSM -R SM | exp

37. 37 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC The Higgs sector in the CP violating MSSM mass eigenstates H 1, H 2, H 3 <> CP eigenstates h,A,H  at Born level: CP symmetry conserved in Higgs sector  complex SUSY breaking parameters (,A t ) introduce new CP phases  mixing between neutral CP eigenstates  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 H 1 from LEP Why consider such scenarios?

38. 38 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC Discovery potential in CP violating MSSM M H1 : < 50 GeV, M H2 : 105 to 115 GeV, M H3 : 140 to 180 GeV, M H+-: 130 to 170 GeV  most promising channel: tt  bW bH +, H +  W H 1, H 1  bb final state: 4b 2j l same as ttH, H  bb  revised studies for H 2/3  H 1 H 1 also interesting

39. 39 Markus Schumacher The Origin Of Mass - Exploring the Higgs Sector at the LHC 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

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

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