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Physics at the LHC, UK HEP Forum, Cosener’s 2011

Physics at the LHC, UK HEP Forum, Cosener’s 2011. LHC Higgs Searches. C. H. Shepherd-Themistocleous PPD, Rutherford Appleton Laboratory. Outline. Results from Higgs searches at the LHC SM Higgs production and Decay Search for SM Higgs at low, medium and High masses

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Physics at the LHC, UK HEP Forum, Cosener’s 2011

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  1. Physics at the LHC, UK HEP Forum, Cosener’s 2011 LHC Higgs Searches C. H. Shepherd-Themistocleous PPD, Rutherford Appleton Laboratory

  2. Outline Results from Higgs searches at the LHC • SM Higgs production and Decay • Search for SM Higgs at low, medium and High masses • Searches for non-SM Higgs • EWK results (brief) Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  3. Luminosity ATLAS CMS • At EPS reported on ~1 fb-1. • At LP many analyses used close to 1.7 fb-1 and even 2.3 fb-1.

  4. Higgs Production https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  5. Higgs Decay Analyses can be classed in approximate mass ranges Low (< 130 GeV) , medium (130-200 GeV) high (> 200 GeV) Searches are characterized by BR and width. Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  6. High masses WW and ZZ modes Intermediate masses WW key channel with best overall sensitivity Low mass H → gg , H-> tautau , VH-> bb Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  7. Key background cross sections

  8. Low mass Higgs searches • Channels for mass range ~ 100-130 GeV • H →  Best sensitivity at low masses • H →  Useful (potential in SUSY scenarios) • H → bb Large BR but rather challenging

  9. H → gg • Rare decay through loops • Irreducible gg backgrounds • Reducible from jets faking photons. jet-jet supression ~ 108 • Require very good mass resolution. ECAL critical. • Photon class (converted or not) plus region of calorimeter • vary resolution. Used to define classes for analyses. • Test of ECAL calibration using Z → ee peak.

  10. Resolution comparison Comparison of resolutions in ATLAS (black) and CMS (blue) using tuned MC. Best case barrel no conversions All categories combined

  11. H → gg • Both experiments divide data into quality classes. • Fit background plus signal shape • No evidence of a signal – set limits 1.6 fb-1 1.08 fb-1

  12. H→ gg • ATLAS 1.08 fb-1CMS 1.66 fb-1. No evidence for SM Higgs • Sensitivity currently 3-4 times SM.

  13. H → tt • Sensitivity in cleaner VBF (non-VBF also used) modes. Both use ll and l-had final states. • Forward tagging jets suppress SM backgrounds. • Main backgrounds: Z + jets (Z→ tt irreducible), W → ln+jets, diboson, top, QCD. • Background suppression makes use of event topology • CMS use visible mass, ATLAS use collinear approx. and estimate mtt. • Fits peformed to spectra. ATLAS ee, em, mm channels QCD, W+jets, Z→ tt from data Other bg MC. CMS e-had example. QCD, W+jets from data Z → tt + rest from MC

  14. H → tt • Combination of large number of channels. • Sensitivity some way off SM, but also useful for SUSY.

  15. H→ bb • Dominant decay mode at low mass BUT QCD background huge. • Interesting because potentially provides information on Higgs to quark coupling. • Searches in VH production and require b-tagging. Backgrounds V+jets, VV, top, QCD. • CMS & ATLAS Z→ ll, W→ ln. CMS also Z → nn ZH → llbb CMS sensitivity rather larger than ATLAS’s

  16. Intermediate mass • Channels for mass range ~ 130-200 GeV • H → WW → llnn Greatest overall sensitivity to SM Higgs

  17. H→ WW → llnn • Excellent sensitivity where this BR is large 130-200 Gev. • Challenging Higgs mass cannot be reconstructed. • Search both latest results cut based. • Look for 2 opp. sign leptons , missing ET. • Jets 0,1 both; 2 (VBF) CMS. • Scalar Higgs - make use of Df(ll) cut. • CMS Major requirements: • Lepton Pt > 10 GeV, tight ID & Isolation • removes QCD & W+jets contamination • Large MET & Z  μμ, ee veto • removes Drell-Yan contamination • Class # of jets (PT > 30 GeV) & b-jet veto • removes Top contamination • Kinematic discriminants: Mll &ΔΦ(l+l-) • mitigates pp  WW background • MH–dependent cut optimization ATLAS similar. Use ETmissrel After ET and pT cuts

  18. H→ WW → llnn 0 jets 1 jet ATLAS Mll after pT cuts on leptons For 0 jet WW dominates for 1 jet increased ttbar. 0 jets 1 jet ATLAS MT after all other cuts

  19. H→ WW → llnn 0 jets 0 jets 1 jet

  20. H→ WW → llnn • Main backgrounds WW, ttbar, D-Y, W+jets, WZ/ZZ. • Estimated from data for major backgrounds, minor use MC. • ATLAS and CMS similar • WW using high mass ll events where no/little signal. • ttbar invert b tagging cut and extrapolate using tagging efficiencies. • W+jets, QCD using fake rate derived from data. • D-Y using ll events inverting Z veto cut and extrapolating. Example of ATLAS Expectations from MC and observation using data driven methods

  21. H→ WW → llnn Selection change 1.5 fb-1 1.7 fb-1 SM Higgs 147 < MH < 194 GeV at 95% CL. Expected sensitivity 136 < MH < 200 GeV SM Higgs 154 < MH < 186 GeV at 95% CL. Expected sensitivity 135 < MH < 196 GeV

  22. High mass • Channels for mass range > 200 GeV • ZZ → 4l • ZZ → 2l2n • ZZ → 2l2q • ZZ → 2l2t • WW→ln2q • WW → 2l2n

  23. H → ZZ(*) → 4l • Clean signal 4 isolated leptons from common vertex. One or two Zs on shell. • Full mass reconstruction. (4e, 4m, 2m2e) • Backgrounds: Zbb, tt. • Suppress with impact parameter and isolation requirements • ZZ Continuum: • Shape known at NLO. • Rate obtained from Z yield in data & theoretical prediction for ratio of ZZ to • Z cross sections PT 43 GeV PT 26 GeV PT 20 GeV PT 48 GeV M4μ = 201 GeV

  24. H → ZZ(*) → 4l CMS Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  25. H → ZZ(*) → 4l Fits to mass spectra performed to extract limits Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  26. H → ZZ→ ll nn • Production of Z with large missing energy • Cut and count analyses in ee and  • Major backgrounds: Z+jets, ttbar, WZ • Cuts on MET, MT, Δ (MET,jet) • Residual backgrounds: • ZZ (NLO+LO),WZ(NLO) from MC • Z+jets estimated from +jet data. • Non resonant ttbar & WW use e events

  27. H → ZZ→ ll nn ATLAS CMS • CMS 1.6 fb-1 , ATLAS 1.04 fb-1 • Exclusion 340-375 GeV (CMS) , 350-450 GeV (ATLAS) @ 95% CL Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  28. H → ZZ(*) → 2l2q • Highest rate for Z channel • Events categorized by presence of 0, 1, 2 b-jets • Mass reconstructed from l and jets. • Major background: Z+jets ; ttbar suppressed by MET requirement • CMS Use 5 angles of scalar H  ZZ  2l 2q in a likelihood discriminant • Background shape, normalization  data sideband CMS Preliminary 1.04 fb-1 1.6 fb-1 Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  29. H → ZZ(*) → 2l2q Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  30. H → ZZ(*) → 2l2t • New CMS analysis. One Z → ll ( 60 < m < 120 GeV); Z → thth , mth , ethem ( 30 < mvis < 80 GeV) • Backgrounds: • ZZ estimated using observed number of Z and ratio of SM s(ZZ)/s(Z). • Reducible Z+jets, ZW+jets, ttbar ,QCD. non-isolated l or jet can fake th. • Fake rate estimated from Z+jet sample. event eeet

  31. H→ WW → ln qq x100 x100

  32. Non-SM Higgs • Searches have started for possible non-SM Higgs. • MSSM SUSY has 5 h,H0,A0,H+/-. CMS F → tt, H+ → tn. • Make use of bbF production (large tanb no VBF) Significant improvement on previous results Tevatron BR limit : 0.15 – 0.2 Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  33. Doubly Charged Higgs • Doubly charged pair produced H++ → l+l+,t+t+ • Arises in models with extra Higgs triplets • F++, F+, F0 • Triplet responsible for small neutrino mass • Unknown neutrino mass matrix unknown branching ratios  broad search • Below M ≈2MW, only leptonic decays 3l f.s. 3 or 4 leptons in final state used for search

  34. All limits CMS Preliminary

  35. CMS combination Analysed data between 1.1-1.7 fb-1 Expected exclusion mass range: 130 – 440 GeV Observed exclusion mass range: 145-216, 226-288, 310-400 GeV Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  36. ATLAS combination Expected exclusion mass range: 130 – 440 GeV Observed exclusion mass range: 146-232, 256-282, 296-466 GeV Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  37. p-values Probability of an upward background fluctuation as high or higher than observed in data Interpretation requires “look elsewhere effect” correction Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  38. Summary of Higgs searches • Large number of searches performed by both ATLAS and CMS. • Impressive work on combinations of results • Similar exclusion regions in each of the experiments. • CMS: 145-216, 226-288, 310-400 GeV • ATLAS: 146-232, 256-282, 296-466 GeV • Excess in low mass range less significant than at time of EPS. • Factor of 2 in integrated luminosity between EPS and LP. • Hope for another similar factor this year.

  39. W mass • Huge production x-section at 7TeV • Pile up a challenge • pdfs affect precision Kinematics important for precision measurement, pT dist. Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  40. TGCs Will profit from increased stats Can search for evidence in NP in deviation from expectations or forbidden vertices. SM vertices WWZ, WWg forbidden ZZZZZg No anomalous coupling observed WW leptonic WW leptonic

  41. THE END

  42. Backup Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  43. Search potential wrt Tevatron Ratio of int. luminosities LHC (40 pb-1) /TEV (5fb-1) ~ 1/100 For ratios of parton luminosities > 100 LHC wins (Fn of initial state) Production of massive objects > ~ 1TeV Pair production of Intermediate mass particles from gg, qg, qq Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

  44. Add table for ATLAS Cosener's Forum 2011 C.H. Shepherd-Themistocleous - RAL

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