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Higgs Boson at LHC: gearing up for discovery

Higgs Boson at LHC: gearing up for discovery. Andrey Korytov. Outline. Introductory remarks: what we already know LHC, ATLAS, and CMS Gold-plated channel SM H ZZ4 m at CMS Other SM Higgs discovery channels A few words on MSSM Higgs (and more if time permits).

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Higgs Boson at LHC: gearing up for discovery

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  1. Higgs Boson at LHC: gearing up for discovery Andrey Korytov

  2. Outline • Introductory remarks: what we already know • LHC, ATLAS, and CMS • Gold-plated channel SM HZZ4mat CMS • Other SM Higgs discovery channels • A few words on MSSM Higgs (and more if time permits)

  3. SM Higgs Trivia: intelligent design • Start from scalar field • doublet pseudo-scalar in SM • Require local gauge invariance • need massless gauge fields A • lagrangian acquires terms • Mexican hat potential • min V(f) is not at f=0 • non-zero vacuum expectation value v0—ether of 21 century • expand around minimum • effective mass terms for gauge bosons • effective mass for h-field itself • Free lunch: • force f interact with fermions with ad hoc couplings lf • effective fermion masses (within the P-violation framework!) • Two important points: • Higgs boson mass is the only free parameter • (Higgs-particle coupling) ~ (mass of particle) • Production mechanisms: first one needs to produce heavy particles • Decay channels: higgs likes to decay to heaviest particles it can decay to

  4. non-perturbative New Physics Energy Scale L (GeV) 103 106 109 1012 1015 1018 unstable vacuum 0 200 400 600 Higgs mass MH (GeV) What we know: theory • After renormalization • l l(Q) • If mH were small at 1 TeV, l runs down with Q, flips sign at some scale Q, and vacuum breaks loose • If mH were large at 1 TeV, l runs up with Q, explodes at some scale, theory becomes non-perturbative, and theorists can retire • SM Higgs has a very narrow window of opportunity to be self-sufficient due to a fine-tuned accidental cancellation of large correction factors

  5. } jet (b-tagged) MJJ=MH =? e- jet (b-tagged) b b H LEP Energy 209 GeV } q Z0 jet Z0 e+ q MJJ=MZ=91 GeV jet What we know: direct search at LEP

  6. ALEPH Collaboration data - 2000 Points—data Dashed line—expected background (no-Higgs processes) Tight Cuts small excess? MH (GeV/c2) What we know: direct search at LEP After taking more data and combining results of all 4 experiments, the final word from LEP: No discovery... Consistency with background: ~1.7s Limit on Higgs mass: MH > 114.4 GeV @95% CL Formally, it looked like 4s effect! If it was Higgs, they saw too many... LEP was let run longer to get more data Phys. Lett. B565 (2003) 61

  7. What we know: direct search at Tevatron • Some lessons: • MH=110 GeV (the best expectations) • SM Higgs exclusion at 95% CL was expected at L=1.2 fb-1 • Now at L~1 fb-1, the excluded limit is almost a factor of 10 worse • MH=160 GeV (the best current limit) • Disparity between the current limit and projected expectations is a factor of 2 • This is not to discredit the excellent ongoing effort (very nice solid analyses!) • It just shows that the reality can be not as rosy as projections---something to remember as we expect the LHC turn-on…

  8. W W H What we know: circumstantial evidence LEP EW Working Group July 2006 • Presence of too light or two heavy Higgs in loops would make various SM precision measurements less self-consistent • mH<166 GeV at 95% CL • mH<199 GeV at 95% CL, if the direct search limit mH>114 GeV is included

  9. France 6 miles Geneva airport Switzerland Large Hadron Collider • 2007 (Dec) • hardware commissioning run • sqrt(s)=900 GeV • Lint ~ 100 nb-1 (0.0001 fb-1) • 2008 • first physics run • sqrt(s)=14 TeV • Lint ~ 0.1-1 fb-1 • 2009 • sqrt(s)=14 TeV • Lint ~ 10 fb-1 • 2010 • sqrt(s)=14 TeV • Lint ~ 20-100 fb-1

  10. ATLAS

  11. Compact Muon Solenoid

  12. President of France J. Chirac is observing live muons detected by the Endcap Muon Chambers. CMS Endcap Muon Chambers We need 500 of them to cover ~1000 m2 muon is detected with ~100 mm precision ~ 4 ns time resolution 1.5 m 3.3 m

  13. CMS Physics Technical Design Report • Physics TDR • Comprehensive/up-to-date overview of CMS physics reach • First part of TDR is devoted to 11 in-depth (showcase) analyses; HZZ4m is one of them • Published last fall 650 pages 308 figures 207 tables 1.50 kg

  14. SM Higgs: discovery signatures at L=30 fb-1 • Colored cells = { detailed studies available } • YES = { sure discovery in the appropriate range of masses at L=30 fb-1 }

  15. ZZ  4 with spectacular peak at m4=mZ (this s-channel contribution was overlookedin all previous studies) Zbb  4 + X tt  4 + X Higgs signal H  4 HZZ4m: dominant 4m backgrounds • tt  Wb + Wb •  mnBX + mnBX •  mn+mnX + mn+mnX •  4m + X • Zbb  mm + BB + X  •  mm + 2(mnX) + X •  4m + X • ZZ  4m s-channel t-channel

  16. HZZ4m: analysis strategy • Peak in m4m distribution • Cut variables: • muon isolation: 2 muons in tt and Zbb appear in B-decays, i.e. within jets • displaced vertex: 2 muons in tt and Zbb appear in B-decays • missing energy: tt will have hard neutrinos • kinematics: muons in Zbb and tt tend to be softer • NOT USED: • pT(4m) for Higgs is larger than for ZZ, but the non-zero pT appears only at NLO, which is not accounted for in the current MC simulation • number of jets for Higgs (ggHZZ) is larger than for ZZ (qqZZ), but this effect of hard jets is again NLO… • Cut optimization • mH-dependent (read m4m-dependent) • identify most important and not-correlated cuts • isolation cut on the least isolated muon (i.e., the same cut for all muons) • muon pT cut for the 3rd softest muon • and produce smooth cut(m4m) functions This strategy makes the search automatically optimized for any mass at which Higgs boson may chose to show up • Peak search: • Include statistics and systematics into significance evaluation • Final probabilistic interpretation (significance dilution due to scanning)

  17. HZZ4m: understanding ZZ bkgd 2 2 + + x + … • Knlo(m4m) • Box-diagram • Control samples • QCD scale uncertainties • PDF scale uncertainties • Isolation cut uncertainties • Muon efficiency uncertainty

  18. Zecher, Matsuura, van der Bij hep-ph/9404295 ~20% over LO HZZ4m: understanding ZZ bkgd • Knlo(m4m) • Box-diagram • Control samples • QCD scale uncertainties • PDF scale uncertainties • Isolation cut uncertainties • Muon efficiency uncertainty Formally (by counting vertices), NNLO However, - it is the LO for ggZZ and - contribution is large due to large gg “luminosity”

  19. HZZ4m: ZZ bkgd • Knlo(m4m) • Box-diagram • Control samples: • qq  Z  2m • very similar origin to ZZ bkgd • huge statistics • ZZ  4m sidebands • would be perfect, if not for rather complicated shape • and very limited statistics • QCD scale uncertainties • PDF scale uncertainties • Isolation cut uncertainties • Muon efficiency uncertainty L=10 fb-1 Total 8 events Exp bkgd 0.8 evts ScL = 4.7

  20. HZZ4m: ZZ bkgd • Knlo(m4m) • Box-diagram • Control samples • QCD scale uncertainties • estimate of higher-order contributions • PDF scale uncertainties • Isolation cut uncertainties • Muon efficiency uncertainty Normalization to Z2m

  21. HZZ4m: ZZ bkgd • Knlo(m4m) • Box-diagram • Control samples • QCD scale uncertainties • PDF scale uncertainties • Isolation cut uncertainties • Underlying Event is the main source for energy flow in vicinity of muons in the irreducible ZZ-bkgd; but UE activity is poorly predicted… • Use data to calibrate UE activity: • UE activity in Z must be very similar to that in ZZ (qq  …) • MC studies confirm this statement • Muon efficiency uncertainty: use data three colors: different UE models — ZZ events - - Z events (random cones)

  22. HZZ4m: ZZ background • Knlo(m4m) • Box-diagram • Control samples • QCD scale uncertainties • PDF scale uncertainties • Isolation cut uncertainties: use data • Muon efficiency uncertainty: use data • single muon trigger; well reconstructed muon m0 • take advantage of muon being measured twice: in Tracker and Stand Alone Muon system • find Z-peak three times… • d(efficiency) ~ 1%

  23. HZZ4m: Higgs signal over ZZ bkgd • Peak search results: • Significance: • Counting Experiment • LLR for m4m spectrum • Luminosity needed • Including systematics

  24. HZZ4m: Higgs signal over ZZ bkgd • Peak search results: • Significance • Luminosity needed • Including systematics

  25. HZZ4m: Higgs signal over ZZ bkgd • Peak search results: • Significance • Luminosity needed • Including systematics • significance must be de-rated • effect depends on how we define the control sample: Z2m peak vs ZZ4m sidebands Calculations done for luminosities, at which the expected significance would be 5, if there were not systematic errors

  26. HZZ4l: combining four channels new

  27. HZZ4m: word of caution Search for Higgs peak Background-only pseudo experiment • Search in a broad range of parameter phase space • mH=115-600 GeV • Probability of finding a local excess somewhere is much higher than naïve statistical significance might imply: e.g. S=3 is almost meaningless • A priori assumptions must be clearly defined — actual probability - - probability implied by local statistical significance

  28. SM Higgs: discovery signatures at L=30 fb-1 • Colored cells = { detailed studies available } • YES = { sure discovery in the appropriate range of masses at L=30 fb-1 }

  29. Standard Model Higgs: Hgg new • Backgrounds: • prompt gg • prompt g + jet(brem g, p0g) • dijet • Analysis: • Cut-based • PT, isolation, Mgg • events sorted by “EM shower profile quality” • Optimized • loose cuts and sorting • event-by-event kinematical Likelihood Ratio • bkgd pdf from sidebands, signal pdf from MC • Systematic errors folded in CMS CMS dMgg < 1%

  30. Standard Model Higgs: HWW2l2n Signal Region Control Sample • Backgrounds: • WW, tt, Wt(b), WZ, ZZ • ggWW (box) • Analysis: • KNLO(pTWW) • cuts: • e/m kinematics, isolation, jet veto, MET • counting experiment, no peak • background from a control sample: • signal: 12<mll<40 GeV • control sample: mem>60 GeV • reduce syst. errors; pay stat. penalty • systematic errors are folded in new CMS

  31. jet f jet h ATLAS Standard Model Higgs: qqH, HWW2l2n Signal Region Control Sample • Backgrounds: • tt, WWjj, Wt • Analysis: • 2 high pT leptons + MET • 2 forward jets (b-jet veto) • central jet veto • counting experiment, no peak: • background from data: • Signal: all cuts • Control sample: no lepton cuts • Result • better than inclusive WW (!!!) ATLAS MH=160 GeV HWWe

  32. Standard Model Higgs: qqH, Htt Httem • Backgrounds: • Zjj, tt • Analysis: • two forward jets, central jet veto • two leptons (e, m, t-jet)+MET • ttlnn + lnn • tt lnn + t-jet • mass(l; l or t-jet; pTmis) • despite 3 or 4 n’s present, works quite well in collinear approximation ATLAS 30 fb-1 ATLAS t pTmis H t

  33. Difficult (impossible) channel: ttH, Hbb if higgs boson is light, can we use Hbb? • CMS: • careful study of systematic errors in the Physics TDR • syst error control at sub-percent level is needed: not feasible... SM Higgs: ttH, Hbb ATLAS 30 fb-1

  34. Standard Model Higgs: Summary new • Benchmark luminosities: • 0.2 fb-1: exclusion limits will start carving into SM Higgs x-section • 1 fb-1: discoveries become possible if MH~170 GeV • 10 fb-1: SM Higgs is discovered (or excluded) in full range NLO cross sections Systematic errors included

  35. mtop=174.3 GeV MSSM Higgs bosons: h, H, A, H± • SUSY stabilizes Higgs mass • 2 Higgs field doublets needed • Physical scalar particles: h, H, A, H± • Properties at tree level • fully defined by 2 free parameters: MA, tanb • CP-even h and H are almost SM-like in vicinity of their mass limits vs MA: hmax and Hmin • large tanb • suppresses coupling to Z and W • enhances coupling to “down” fermions: b and t are very important! • CP-odd A never couples to Z and W: • decays: bb, tt (and tt for small tanb) • H± strongly couples to tb and tn • all Higgs bosons are narrow (G<10 GeV) • Loop corrections • gives sensitivity to other SUSY parameters • mhmax scenario = { most conservative LEP limits }

  36. ATLAS L=300 fb-1 MSSM Higgs or SM Higgs? • SM-like h only: • considerable area… • even at L=300 fb-1 • Any handles? • decays to SUSY particles? • SUSY particle decays? • measure branching ratios?

  37. Summary • Standard Model Higgs: • expect to start excluding SM Higgs at L~0.1 fb-1 • discoveries may be expected already at L~1 fb-1 • SM Higgs, if that’s all we have, is expected to be discovered by the time we reach L~10 fb-1 • MSSM Higgs: • nearly full (M, tanb) plane is expected to be covered at L~30 fb-1 • there is a serious chance to see only a SM-like Higgs…

  38. Backup: SUSY Higgs Plots

  39. MSSM Higgs boson: h, H, A production h H A • x-sections are large, often much larger than SM (dotted line) • bb(h/H/A) production is very important tanb=3 h H A tanb=30

  40. MSSM Higgs: SM-like signatures • ATLAS: • no systematics included • CMS: • better detector simulation • systematics included • contours recessed… CMS 2003 CMS 2006 new ATLAS

  41. ATLAS MSSM Higgs: heavy neutral H, A • production in association with bb (especially good at large tanb) • bb-decay mode (~80%) is overwhelmed with QCD background • tt-decay mode (~20%) is the next best • mm-decays (~0.1%) allow for direct measurement of G • better detector simulation (i.e. more realistic) • systematics included • contours recessed (low MA band, qqH, moved to SM-like Higgs plot) CMS 2003 CMS 2006 new

  42. MSSM Higgs: H± • Heavy H± (M>mt): • production via gg  tbH± bjj+btn and gb  tH± bjj+tn • H± tn (H± tb overwhelmed by bkgd) • tWbjjb • backgrounds: tt, Wt, W+jets • Light H± (M<mt): • production via gg/qq  tt  btn+bln • t H±b, H± tn • tWblnb • backgrounds: tt, Wt, Wjjj new

  43. Difficult (impossible) channels… MSSM Higgs: H±tb MSSM Higgs: bb(H/A), (H/A)bb

  44. MSSM Higgs bosons: h, H, A, H± • Loop corrections give sensitivity to the rest of SUSY sector, more specifically to: • stop quark mixing Xt • squark masses MSUSY • gluino mass Mg • SU(2) gaugino mass M2 • higgsino mass parameter m • Special benchmark points*: • max stop mixing (mhmax): • mh < 133 GeV • MSUSY~1 TeV • most conservative LEP limits • no mixing: • mh < 119 GeV • MSUSY~1 TeV • gluophobic h • ggh is suppressed (top+stop loop cancellation) • mh < 119 GeV • MSUSY~350 GeV • small aeff (mix h/H): • tt and bb-decays suppressed even for large tanb • mh < 123 GeV • MSUSY~800 GeV *Suggested by Carena et al. , Eur.Phys.J.C26,601(2003)

  45. MSSM Higgs: other benchmark points? • ATLAS studies: • preliminary (no syst) • vector boson fusion: • qq(h/H) • h/Htt, WW, gg • caveat for small aeff: decoupling from tt is compensated by WW enhancement • all four special points are well covered at L=30 fb-1

  46. ATLAS L=300 fb-1 MSSM Higgs or SM Higgs? • SM-like h only: • considerable area… • even at L=300 fb-1 • Any handles? • decays to SUSY particles? • SUSY particle decays? • measure branching ratios?

  47. MSSM Higgs or SM Higgs? • BR for different channels: • R = BR(hWW) / BR(htt) • D=|RMSSM-RSM|/sexpimental • Decays to SUSY: • hc20c20(2lc10)+(2lc10) • Signature: • Four leptons • Large MET Msleptons=250 GeV ATLAS 300 fb-1

  48. MSSM Higgs: yet another twist • ATLAS preliminary • qqH, HWW, tt • bbH, Htt, mm • tbH± and tH±, H±tn • … • CP-violation in Higgs sector • complex couplings: • mass eigenstates H1, H2, H3 are mixtures of h, H, A • production/decay modes change • new benchmark point CPX (maximum effect) suggested by Carena et al., Phys.Lett B495 (2000) 155 • new parameterization: MH± ; tanb ATLAS L=30 fb-1 • uncovered holes remain • more studies needed not excluded at LEP

  49. Backup: ATLAS/CMS Summary Plots

  50. SM Higgs CMS 2003 CMS 2006 new

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