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Higgs Studies at the LHC and the ILC

Higgs Studies at the LHC and the ILC. Albert De Roeck CERN SUSY 2005 18-23 July Durham . The Higgs Mechanism. Higgs, Englert and Brout propose to add a complex scalar field to the Lagrangian. Expect at least one new scalar particle: The (Brout-Englert-) Higgs particle.

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Higgs Studies at the LHC and the ILC

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  1. Higgs Studies at the LHC and the ILC Albert De Roeck CERN SUSY 2005 18-23 July Durham

  2. The Higgs Mechanism • Higgs, Englert and Brout propose to add • a complex scalar field to the Lagrangian Expect at least one new scalar particle: The (Brout-Englert-) Higgs particle • SM Higgs (LEP) • MH>114.1 GeV @95% CL • MSSM neutral Higgs bosons (LEP) • Mh, MA>92.9, 93.3 GeV @95% CL • MH± >89.6 GeV @95% CL for BR(MH±→ τν) =1 • MH± >78.6 GeV @95% CL for any BR • Electroweak fits to all high Q2 measurements give: • MH=98+52-36 GeV (old top mass) • MH<186 GeV @ 95% CL (“yesterdays” new top mass) • Tevatron searches see C. Tully’s talk Probably the most wanted particle in HEP Discover … or prove that it does not exist

  3. High Energy Frontier in HEP Next projects on the HEP roadmap • Large Hadron Collider LHC at CERN: pp @ 14 TeV • LHC will be closed and set up for beam on 1 July 2007 • First beam in machine: August 2007 • First collisions expected in November 2007 • Followed by a short pilot run • First physics run in 2008 (starting April/May; a few fb-1? ) • Linear Collider (ILC) : e+e- @ 0.5-1 TeV • Strong world-wide effort to start construction earliest around 2009/2010, if approved and budget established • Turn on earliest 2015 (in the best of worlds) • Study groups in Europe, Americas and Asia (World Wide Study) M. Lamont Tev4LHC meeting @ CERN (April) Quest for the Higgs(*) particle is a major motivation for these new machines (*) will discuss mostly the Standard Model Higgs in this talk

  4. “Higgs Roadmap” • Discover the Higgs (in the range 114.4 GeV < MH < 1 TeV) • Determine its properties/profile • The mass • Spin and parity quantum numbers • How does it decay? • Measure Yukawa like patterns • Measure relations between fermion and gauge boson couplings • Observe rare decay modes • Observe unexpected decay modes? (new particles?) • Measure total width • Reconstruction of the Higgs potential by determination of the Higgs self coupling • Its nature: is it standard, supersymmetric, composite. BOTH LHC and LC will be crucial in establishing Higgs Dynamics

  5. LHC: pp Collisions at 14 TeV • ~20 min bias events overlap at 1034cm-2 s-1 • HZZ Z mm H 4 muons the cleanest (“golden”) signature This (not the H production !!) repeats every 25 ns…

  6. SM Higgs production NLO Cross sections M. Spira et al. gg fusion IVB fusion

  7. SM Higgs search channels Low mass MH ≲ 200 GeV M. pieri Intermediate mass (200 GeV ≲ MH ≲700 GeV) High mass (MH ≳ 700 GeV) • VBF qqH →ZZ →ℓℓνν • VBF qqH →WW →ℓνjj • inclusive H → WW • inclusive H → ZZ H → γγ and H → ZZ* → 4ℓ are the only channels with a very good mass resolution ~1%

  8. Examples High MH > ~500 GeV/c2 Medium 130<MH<500 GeV/c2 Low MH < 140 GeV/c2

  9. Vector Boson Fusion Channels Dokshitzer, Khoze, Troyan; Rainwater, Zeppenfeld et al. ppqqH +X Higgs and two forward jets (|| ~ 3) Results 30fb-1 Tag jets to reduce background With these new channels each experiment can discover the Higgs with 5 with 30 fb-1

  10. Other Channels (Hbb) S/B=0.03 S/B=0.3 30 fb-1 Not discovery channels but can be used to confirm/measure couplings

  11. gap gap H p p -jet Diffractive Higgs Production SM Higgs: Cross section ~3fb (Khoze et al) MSSM: s ~ x10 larger (tan) h 100 fb • Exclusive production: •  Jz=0 suppression of ggbb bkg • Higgs mass via missing mass • CP structure of the Higgs from angular distribution of the protons • Of course, need Roman potsFP420 project 1fb Kaidalov et al., hep-ph/0307064 M = O(1.0 - 2.0) GeV 120 Also HWW*

  12. LHC Reach for a Higgs Discovery Total sensitivity Different channels 30 fb-1 2-3 years LHC can cover the whole region of interest with 10 fb-1

  13. Mass and Width Resolution ATLAS PTDR 5-8% 0.1-1% MSSM HiggsDm/m (%) 300 fb-1 h, A, H  gg0.1-0.4 H  4  0.1-0.4 H/A  mm 0.1-1.5 h  bb 1-2 H  hh  bb gg 1-2 A  Zh  bb  1-2 H/A  tt 1-10 Analysis of indirect widthsfor mass range below 200 GeV: 10-20% precision

  14. Branching Ratios and Couplings Precision on BR Ratios of couplings With “mild” theoretical assumptionscouplings Cannot determine total Higgs cross section No absolute meas. of partial dec. widths Duhrssen et al., hep-ph/0406323 Precision 10-40 (20)% Assume (within 5%) Also measurement of H Dominated by luminosity uncertainty Precision 10-40%

  15. Higgs rest frame Spin and CP-quantum Numbers: H  ZZ4l ATLAS 100 fb-1 •  MH>250 GeV: distinguish between S=0,1 and CP even.odd •  MH<250 GeV: only see difference between SM-Higgs and S=0, CP=-1 •  , less powerful

  16. Heavy MSSM Higgs Search • H   • H  tb • A/H   • A/H   • A/H bb/  in bb H/A MSSM 5 Higgses: h,H,A,H At low tan , we may exploit the sparticle decay modes: Contours for 5  discovery MHMAX scenario New: includes VBF channels  A, H 20 20  4l+ ETmiss  A, H in cascade decays of sparticles

  17. CP Violating Scenario M. Schumacher • CP eigenstates h, A, H mix to mass eigenstates H1, H2, H3 • maximise effect  CPX scenario(Carena et al., Phys.Lett B495 155(2000)) • arg(At)=arg(Ab)=arg(Mgluino)=900 Small area remains uncovered Could be covered by MH1 < 70 GeV (not studied yet) Significant dependence on the top mass (now 172.7±2.9 GeV)

  18. Higgs Studies at an e+e- Linear Collider •  L > 1034cm-2s-1 80% electron polarization •  Energy flexibility between √s = 90-500 GeV • Future: possibility of γγ, e-e-, e+ polarization, Giga –Z Can detect the Higgs via the recoil to the Z e.g. Desch Bataglia LCWS00  Fully simulated+reconstructed HZ event  Backgrounds low  Robust signal: if (eeH+x) 100 times lower, still observable Observation of the Higgs independent of decay modes

  19. Higgs Production at an e+e- Linear Collider Dominant production processes at ILC: ZH H  ~ln(s) Example: s=350 GeV mH = 120 GeV L= 500 fb-1 (~2-4 years) ~90 K Higgs events produced  ~1/s

  20. Higgs Mass Measurement Garcia-Abia, et al., hep-ex/0505096 s= 350 GeV 500 fb-1 Beam systematics included Determine the Higgs mass to about 40-70 MeV How much can theory handle/does theory want?

  21. Higgs Branching Ratios Tim Barklow, LCWS04 • Model independent • Absolute branching ratios! Normalized to absolute HZ cross section •  Precise measurements: few % to 10%. •  Special options to improve further e.g. BR(H) ~ 2% at photon collider

  22. Extraction of Higgs Couplings • Use measured branching ratios to extract Higgs couplings to fermions • and bosons • Global fit to all observables (cross sections and branching ratios) & take into account correlations • The precise determination of the effective couplings opens a window • of the sensitivity to the nature of the Higgs Boson TESLA-TDR values

  23. Rare Higgs Decay Modes • Rare Higgs decay modes become accessible eg • Hbb at higher masses (Yukawa couplings) • H • HZ gH/gH ~15% for 1 ab-1 Hbb gHbb/gHbb ~17% for 1 ab-1

  24. H,A Search at a Photon Collider J. Gunion et al. M. Krawczyk et al.  Extent discovery range to close to kinematic range= 0.8Ecms(e+e-) Measurement of / to10-20% with 1 year of data

  25. Invisible Higgs Decays Invisible Higgs decays –Higgs decay in undetected particles- can be observed directly in ZH events  Observe a peak in the recoil mass of ZH events Sum of width Branching ratio can be determined with good precision: Better than 5% for large enough branching ratios Recoil

  26. Spin and CP Quantum Numbers  At threshold: determine J from the  dependence of ZH  At continuum: use angular distributions to determine CP composition HZ production + also H

  27. Top-Higgs Yukawa coupling • The top-Higgs Yukawa coupling is very large (gttH ~ 0.7 while gbbH ~ 0.02). Precise measurements important since could could show largest deviations to new physics • Needs 0.8-1.0 TeV collider and large luminosity • If mH<2mt e+e- ttH • If mH>2mtmeasure BR(Htt)

  28. LHCLC data: Top Yukawa coupling Dawson, Desch, Juste, Rainwater, Reina, Schumacher, Wackeroth Assume a light Higgs < 2mt Production processes LC: e+e-  ttH No precise measurement at 350-500 GeV LC LHC: gg  ttH measures •BR (ttbb,ttWW) depends on g2ttH g2bbH and g2ttH g2WWH g2bbH and g2WWH can be measured precisely in a model independent way at the ILC (few %)   can determine g2ttH without any model assumptions LHC alone~ 0.3 (and model dependent) ILC 350 GeV 500 fb-1

  29. Measuring the Higgs Potential  Measure the Higgs self-coupling: HH production Larger precision at higher energies Eg CLIC: a 3 to 5 TeV LC MH = 240 GeV 180 GeV 140 GeV 120 GeV LHC: gHHH (3000 fb-1) for 150<MH<200 GeV

  30. ~3 years ~1 year 5  discovery mH > 114.4 Summary: Higgs at the LHC and LC • Higgs can be discovered over full allowed mass range in 1 year of (good) • LHC operation •  final word about SM Higgs mechanism • However: it will take time to understand and calibrate ATLAS and CMS • If Higgs found, mass can be measured to 0.1% up to mH~ 500 GeV • A LC will provide precision measurements on absolute couplings ~%, quantum • numbers (spin, CP…), rare decays of the Higgs, and the Higgs potential • A LC aims for a full validation of the Higgs Mechanism

  31. LHC Higgs Summary • LHC will discover the SM Higgs in the full region up to 1 TeV or exclude its existence. If no Higgs, other new phenomena in the WW should be observed around 1 TeV • The LHC will measure with full luminosity (300 fb-1) • The Higgs mass with 0.1-1% precision • The Higgs width, for mH> 200 GeV, with ~5-8% precision • Cross sections x branching ratios with 6-20% precision • Ratios of couplings with 10-40% precision • Absolute couplings only with additional assumptions • Spin information in the ZZ channel for mH>200 GeV

  32. ILC Higgs Summary • The Higgs cannot escape the ILC, if within its kinematical range • The Higgs mass can be measured down to 40-70 MeV • Absolute branching ratios can be determined to the % level • Couplings can be determined to the % level • Note new phenomena such as heavy vector bosons or Higgs triplets give contributions to the Higgs couplings of O(5%) • Rare decay modes can be studied • Invisible decay modes can be detected (to some level also at the LHC) • Spin and CP quantum numbers can be determined • The Higgs potential can be measured (particulalry with a multi-TeV LC) • LHC+ILC(500) combined data give the best top-yukawa coupling measurement

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