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Search for the SM Higgs Bosons at the LHC

Explore the search for the Standard Model Higgs Bosons at the Large Hadron Collider. Understanding the symmetries, interactions, and implications of the Higgs mechanism. Discover the significance of the Higgs boson in regulating energy calculations and its role in potential unification theories. Delve into the unitarity constraint, theoretical constraints, and implications for new physics at the TeV scale. Learn about the challenges, constraints, and expectations in the quest for the elusive Higgs Bosons.

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Search for the SM Higgs Bosons at the LHC

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  1. Search for the SM Higgs Bosons at the LHC The first 1 fb-1 Yves Sirois LLR EcolePolytechnique CNRS-IN2P3 D0 Meeting, Paris - 10/2008

  2. Opening Remarks (1) • Electroweak and Strong Interactions: Yang-Mills quantum field theory with local gauge SU(3)SU(2)U(1) symmetries Symmetry groups  gauge bosons Representation (arbitrary)  particles Chiral structure of matter, i.e. different EW quantum numbers for R and L chiralities of the fermions  forbids mass terms  need a EW symetry breaking • A spontaneous symetry breaking preserves renormalisibility in EW sector while giving masses to the Z and W bosons (short range weak interaction) and maintaining a null mass for the  (infinite range of electromagnetism) SM Mecanism  doublet of scalar fields under SU(2)  one physical boson of mass MH2 = 2  v2 with v = (2 GF)-1/2 ~ 246 GeV [Fermi scale] • Focus here: the road towards Higgs boson(s) discoveries at low LHC luminosities For the measurements needed to establish that a signal actually is due to the quanta of the scalar field responsible for EW symmetry breaking (in SM or MSSM or beyond) like MH, SCP, gauge couplings, self-coupling etc. ...  talk by K. Jacobs (this workshop) D0 Meeting, Paris - 10/2008

  3. • Fermions acquire a (arbitrary) mass by interacting with the scalar field (with arbitrary couplings) … the stucture and family replica, etc. remain unexplained • The Higgs boson allows to regulate the calculations towards high energies … and allows to contemplate a quasi-unification (unification) of couplings at some Grand Unification scale  more symmetries  new bosons (interactions) • The H mass has to be stabilized at EW scale (hierarchy problem)  talk by B. Heinemann (this workshop) Opening Remarks (2) • The Standard Model SU(3) x SU(2) x U(1) of EW and Strong interactions is remarkably confirmed by experiments since many decades … The SM Lagragian is the most general that is compatible with the symmetries … and conserves the leptonic and baryonic quantum numbers (as observed) … but it is incomplete and unsatisfactory ! D0 Meeting, Paris - 10/2008

  4. Why the LHC ? The search and discovery of the Higgs Boson(s) remains a most important motivation* for the LHC scientific adventure It is an essential and necessary ingredient of the current understanding of matter and fundamental interactions It most likely lies on the critical path towards new territories (hierarchy, SUSY, GUT …) * besides producing micro black holes to swallow sub-primes (and the earth) and thus resolve the economy crisis You mean all that thing does is crack wallnuts ??… D0 Meeting, Paris - 10/2008

  5. The Higgs Boson and Unitarity Reminder: Unitarity Constraint Without a Higgs boson: theory valid for E < 1.2 TeV With the Higgs boson: theory valid if MH< 780 GeV/c2 To avoid unitarity violations (scattering probability > 1) … the Higgs Boson must be discovered … or a new physics  at the TeV scale • Needed: EW ~ 500 GeV • q ~ 1 TeV spp ~ 14 TeV D0 Meeting, Paris - 10/2008

  6. Theory The Higgs Boson SM Reminder: 1 doublet of Higgs Fields  1 physical boson (CP-even) MH is a free parameter … MH2 = 2  v2 ; v ~ 246 GeV K. Riesselman, hep-ph/9711456 Theoretical Contraints: Unitarity: ‘‘Triviality’’ (Higgs self-coupling remains finite :) Trivialité Zone Interdite ‘‘Stability’’ of vacuum: Zone Permise Stabilité Zone Interdite  = cut-off scale D0 Meeting, Paris - 10/2008

  7. Theory Higgs Boson and ‘‘Fine-Tuning’’ Kolda & Murayama, JHEP 7(2000)35 MH > 2 MZ disfavoured by indirect constraints (radiative corrections) Domain favored by experiments MH excluded by direct searches at LEP D0 Meeting, Paris - 10/2008

  8. Theory Disfavoured (Indirect Exclusion; 95%CL) Excluded (direct) Higgs Boson and ‘‘Fine-Tuning’’ Kolda & Murayama, JHEP 7(2000)35 MH > 2 MZ défavorisé par les contraintes indirectes (corrections radiatives) Domaine favorisé par l’expérience MH exclu par recherches directe au LEP D0 Meeting, Paris - 10/2008

  9. The Higgs Boson and the LHC Excluded Disfavoured Production Modes and Cross-sections H0 Production CTEQ6M, Mt=175 GeV used for PTDR BSM Physics can change these in a major way !!! (e.g. bbH in MSSM) D0 Meeting, Paris - 10/2008

  10. 3 From Chicago to Geneva LHC Tevatron Ratio of Higgs to EW cross-sections favorable ! Ratio of EW cross-sections to QCD favorable ! [background “candles”] W, Z Relative increase of the tt background e.g. H  ZZ*  4l l=e, MH = 150 GeV/c2 HZZ* BR  acc.~ O(10) fb tt Higgs QCD ~ 1014 fb Need a ‘‘inhuman’’ reduction of 1013 ! Evolution of the Cross-Sections e.g. SM gg  H avec H  ZZ*, WW*  BR  acc.~ 50  Tevatron Higgs @ LHC  state of the art of ‘‘hadron collider’’ and ‘‘rare decay techniques’’ D0 Meeting, Paris - 10/2008

  11. 3 The Higgs Boson at the LHC Observability A. Djouadi, hep-ph/0503172 MH 145 GeV H  bb Dominant mode … but crippling QCD background … may be exploitable in the associated mode Htt ? BSM Physics can change these in a major way !!! (e.g. , bb in MSSM) H   Exploitable at low MH in the VBF production mode H   Complementary mode at low MH via loop diagrams, low BR but excellent /Jet ( ID,  Iso., M) separation H  WW(*) Dominant mode, ll channel optimal for MH = 2 MW ; lqq’ channel exploitable at large MH or through VBF MH > 125 GeV H  ZZ(*) Small BR but ‘‘golden mode’’ for a discovery ll l l D0 Meeting, Paris - 10/2008

  12. The Higgs boson and the LHC ‘‘ Start-up Low Luminosity’’ L = 1032 cm-2 s-1  1 fb-1 Nominal ‘‘Low Luminosity’’  30 fb-1 L = 1033 cm-2 s-1 10 fb-1/year Nominal ‘‘High Luminosity’’  300 fb-1 L = 1034 cm-2 s-1 100 fb-1/year sLHCL= 1000 fb-1/year Le LHC pp spp = 14 TeV • Needed: EW ~ 500 GeV • q ~ 1 TeV spp ~ 14 TeV D0 Meeting, Paris - 10/2008

  13. CMS and ATLAS The Experiments ATLAS CMS Si actif: 200 m2 LAr : 175k canaux Tracking  2.5, B  4T • Si pixels and strips Calorimetry em  2.5 had 5 • EM: homogeneous PbWO4 crystals • HAD: Cu-Zn/scint. + Fe/Quartz Muon Spectrometer  2.7 • Solenoïd return yoke instrumented Tracking  2.5, B  2T • Si pixels and strips • Transition radiation detector Calorimetry  5 • EM: sampling; Pb/LAr accordeon • HAD: Sampling Fe/scint. + Cu-W/LAr Muon Spectrometer  2.7 • Air-core toroids with muon chambers D0 Meeting, Paris - 10/2008

  14. From dream to reality: CMS D0 Meeting, Paris - 10/2008

  15. From dream to reality: ATLAS D0 Meeting, Paris - 10/2008

  16. September 10 Cruzet4 Cruzet3 Cruzet2 Cruzet1 Detector Commissioning with Cosmics Real Data ! Transverse IP residuals D0 Meeting, Paris - 10/2008

  17. SM Commissioning with First Data 10 pb-1 Monte Carlo Z W Cross-section ‘‘Measurements’’ ‘‘SM expectation’’: ‘‘SM expectation’’: CMS PAS 2007/002 D0 Meeting, Paris - 10/2008 CMS PAS EW 08-005

  18. SM Commissioning with First Data 10- 100 pb-1 Monte Carlo tt  + jets Di-lepton 10 pb-1 Entries 100 pb-1 M3 (GeV/c2) Expected Precision for the cross-section in the di-lepton channel for 100 pb-1 / = 4(stat)  4(syst)  2(pdf)  5(lumi) % D0 Meeting, Paris - 10/2008

  19. SM Commissioning with Early Data Monte Carlo WZ 300 pb-1 CMS D0 Meeting, Paris - 10/2008

  20. VBF e.g. Discovery Reach (Overview) Inclusive Channels: PTDR 2006 D0 Meeting, Paris - 10/2008

  21. e.g. Discovery Reach (Overview) Inclusive Channels: PTDR 2006 D0 Meeting, Paris - 10/2008

  22. Higgs boson at the LHC H  WW(*)  2l2 Inclusive Modes SM Higgs can be discovered in H  WW* over a wide mass range Most sensitive around MH ~ 2 x MW [MH ~ 170 GeV excluded at Tevatron 95% CL] Background: Reducible tt, Wbt, W+jet(s) with fake leptons Irreducible WW* continuum MH=160 WW*¨Cont. tt NLO 2.3 pb 114 pb 840 pb Event Selection: 2 isolated leptons  at high enough PT mid-range Etmiss Central jet veto Small ll (e.g. ll  45°) Max Mll D0 Meeting, Paris - 10/2008

  23. Higgs boson at the LHC H  WW(*)  2l2 Inclusive Modes e.g. cut-based analysis CMS Note 2006/047 Results essentially unchanged from previous studies with fast simulation D0 Meeting, Paris - 10/2008

  24. Higgs boson at the LHC H  WW(*)  2l2 Inclusive Modes Main data-driven emphasis on Control of top background / jet veto systematics Control of lepton fake rates from data (use QCD di-jets etc.) Masterize MVA technique already at start-up ! D0 Meeting, Paris - 10/2008

  25. e.g. Discovery Reach (Overview) Inclusive Channels: PTDR 2006 D0 Meeting, Paris - 10/2008

  26. Higgs boson at the LHC The ``Golden Mode’’ : H  4l Inclusive Modes H  ZZ(*) ee  Signal: 4e, 4, 2e2 (2x) CMS Narrow resonance, low background Background: Reducible: tt , Zbb Irreducible: continuum ZZ(*) Selection: 4 isolated emerging from primary vertex 2 pairs of matching flavours and opposite signs caution: 4 Beware of lepton efficiency at very low PT !!! D0 Meeting, Paris - 10/2008

  27. Higgs boson at the LHC H  4l Analysis (PTDR) Inclusive Modes Analysis assuming optimal performances with ∫L dL = 30 fb-1 CMS-Note 2006/136 Here shown: signal and background at the L required for a 5  discovery CMS CMS Note: • Les corrections NLO pour le continuum ZZ(*) dépendent de M4l • Le bruit est soit mesuré des ‘‘side-bands’’, soit déduit par normalisation ZZ/Z D0 Meeting, Paris - 10/2008

  28. Higgs boson at the LHC H  ZZ*  4l at low L Inclusive Modes Emphasis on: • Control/optimize lepton measurement and lepton isolation efficiencies (use Z in tag-and-probe) … go for the highest  which is just sufficient !) • Very low PT leptons (>50% below 10 GeV/c for MH=130 GeV/c2)  need to combine tracking and calorimetry (internal/external detectors) for e (mu) • Must get MH right by the time we arrive to first hints • Not enough side-bands !  better predict ZZ* continuum from measured Z … but need a good understanding of ZZ* shape (and there are non-trivial gg ZZ* contributions of up to 20%) • A full analyses at start-up luminosities ∫L dL = 1 fb-1 assuming realistic 100 pb-1 detector knowledge and performances show capability of almost full suppression of tt and Zbb backgrounds event even at low MH (exploit more stringent cuts on the least isolated/lowest PT leptons) Expect: between 1 and 10 signal events observed (depending on MH) with S/B from in the range 2 to 4. • Sanity checks: relax flavour and sign requirements and exploit combinatorial D0 Meeting, Paris - 10/2008

  29. Electrons and photons at the LHC Not so … transparent ! CMS ATLAS The electrons initiate showers (e.g. 40-80%)  Identification and efficiency problems, charge mis-identification The photons convert (e.g. 20-40%) in ee pairs before reaching the ECAL D0 Meeting, Paris - 10/2008

  30. e.g. Discovery Reach (Overview) Inclusive Channels: PTDR 2006 D0 Meeting, Paris - 10/2008

  31. Higgs boson at the LHC H   Inclusive Modes Signal: Solenoïd Mode rare: Br ~ 2  10-3 HCAL Recherche d’un pic étroit sur un fond (localement) ~ plat ECAL • Important à basse masse •  BR  99  65 fb MH = 115  140 GeV/c2 Silicon Tracker Bruit de fond: Irréductible: 2  réels (Born + box diagrams) Muon System Réductible: 1  réel QCD di-jets +  + jet(s) CMS-Note 2006/112 D0 Meeting, Paris - 10/2008

  32. Higgs boson at the LHC H   Inclusive Modes CMS-Note 2006/112 Suppression du bruit de fond   ID et  Isolation Signal x 10 Propriétés du bruit de fond mesurées dans les ‘‘side-bands’’ MH = 120 GeV/c2 L = 7.7 fb-1 Signal x 10 MH = 120 GeV/c2 L = 7.7 fb-1 Coupure NN relâchée Coupure NN forte Réseau de Neurones exploitant classification des photons (S/B par événement) + propriétés spéficiques du signal (implicite PT, , VBF/gg, …) D0 Meeting, Paris - 10/2008

  33. Higgs boson at the LHC preliminary preliminary preliminary H   H+ETmiss+ 1l S/B  2 ttH WH inclusive S/B  .03 preliminary H+1j S/B  .08 VBF + more jets with gg H H+ETmiss S/B  2 ZH WH preliminary Different S/B for different sub-channels  Divide and Conquerstrategy H+2j S/B  .4 VBF mainly D0 Meeting, Paris - 10/2008

  34. Higgs boson at the LHC H   Lrequired for a 5  discovery: CMS NN: Kinematics + photon categories Combined fit: selection observables + photon catagories Small systematics on background (side-bands) Note: ~ 20% uncertainty on expected signal) D0 Meeting, Paris - 10/2008

  35. Higgs boson at the LHC Jet vers l’avant Jet vers l’avant Vector Boson Fusion (VBF) Zeppenfeld et Rainwater (1997) Forward (quark) jet tags (jet veto in central region) Higgs boson decay products in central region (trigger) Higgs boson gets a PT kick  ’s generally not back-to-back Modes de désintégration étudiés: qq (V V*)  qq’H; H    (l) (l-)  (l) (jet ) H  H WW* (l)(l- )  (l)(jet jet’) M : possible via e.g. approx. colinéaire pour les produits de désintégration des  (si les  ne sont pas acolinéaires) … résolution dépendant de ETmiss D0 Meeting, Paris - 10/2008

  36. Higgs boson at the LHC e.g. Discovery Reach (Overview) Higgs discovery potential in VBF with 30 fb-1 qqH,H→tt→lj: 4s 115-145GeV qqH ,H→gg: 2s115-135GeV qqH ,H→WW→lnjj: 5s140-200GeV • High L in talk by K. Jacobs (this workshop) D0 Meeting, Paris - 10/2008

  37. 3 Le Boson de Higgs au LHC H H VBF H   • Queue de Z  dans la zone du signal (e.g. pour MH < 130 GeV) Contrôle à partir des données en utilisant des vrai/faux Z  construit à partir d’événements réel Z  en remplaçant les  par une simulation MC de  D0 Meeting, Paris - 10/2008

  38. Z mass shape from Z data VBF selection: Mjj >400 GeV, Dhj1j2>2.5 ptm >10 GeV |hm|<2.4 70<Mmm<110 GeV Inclusive Drell-Yan Uncertainty dominated by modeling of Etmiss (pileup, underlying event, calor. noise & response, …) Z events : ’s substituted by simulated ’s with ’s kinematics to model background shape Higgs boson signal in tail of Z peak: understanding DY di-t mass shape important D0 Meeting, Paris - 10/2008

  39. Expected  mass distribution for 1 fb-1 Relaxed VBF selection for 1 fb-1 analysis Full di- mass using collinear approximation of neutrinos from the  decays and the visible  decay products D0 Meeting, Paris - 10/2008

  40. Expected Exclusion limits for 1 fb-1 of data D0 Meeting, Paris - 10/2008

  41. We have seen Cosmics … e.g. Cosmic Muon Slicing … … through CMS D0 Meeting, Paris - 10/2008

  42. We have seen the LHC beam … 10 September 2008 D0 Meeting, Paris - 10/2008

  43. The very first beam-splash event from the LHC in ATLAS on 10:19, 10th September 2008 Online display Offline display 43 D0 Meeting, Paris - 10/2008 LHCC, 24-Sep-2008, PJ Status of ATLAS

  44. Halo Muons in CSCs and HB CMS Center Meyrin CMS Centre Meyrin Beam pîck-up monitors First beam through CMS ! Jim Virdee Fabiola Gianotti CMS Center Meyrin D0 Meeting, Paris - 10/2008

  45. We have seen Higgs CMS Experiment Peter Higgs visiting the LHC in April 2008 Peter Higgs D0 Meeting, Paris - 10/2008

  46. We are eagerly awaiting for the first collisions ! D0 Meeting, Paris - 10/2008

  47. Higgs Boson announcement Freely adapted from P. Grannis D0 Workshop Higgs discovery to be announced at a CERN seminar* by CMS and ATLAS * open-air field rented to a local farmer D0 Meeting, Paris - 10/2008

  48. Higgs Boson announcement * … always blame the machine for delays Higgs discovery to be announced at a CERN seminar* by CMS and ATLAS * open-air field rented to a local farmer Are there lessons (e.g. for BSM in Run 2) ? D0 Meeting, Paris - 10/2008

  49. Disclaimer In this talk: assume standard LHC configurations at 14 TeV Consider knowledge (detector systematics, backgrounds) in steps of integrated luminosities at 10 pb-1 100 pb-1 … 1fb -1 D0 Meeting, Paris - 10/2008

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