Higgs Studies at the LHC and the ILC Albert De Roeck CERN SUSY July Durham

The Higgs Mechanism 1964 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) –M H >114.1 CL MSSM neutral Higgs bosons (LEP) –M h, M A >92.9, 93.3 CL –M H ± >89.6 CL for BR(M H ± → τν) =1 –M H ± >78.6 CL for any BR Electroweak fits to all high Q 2 measurements give: –M H = GeV (old top mass) –M H <186 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

High Energy Frontier in HEP Next projects on the HEP roadmap Large Hadron Collider LHC at CERN: 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) : 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) (*) will discuss mostly the Standard Model Higgs in this talk Quest for the Higgs (*) particle is a major motivation for these new machines M. Lamont Tev4LHC CERN (April)

“Higgs Roadmap” BOTH LHC and LC will be crucial in establishing Higgs Dynamics Discover the Higgs (in the range GeV < M H < 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.

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

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

SM Higgs search channels Production DECAY InclusiveVBFWH/ZHttH H → γγ YES H → bb YES H → ττ YES H → WW * YES H → ZZ *, Z  ℓ + ℓ -, ℓ=e,μ YES H → Zγ, Z → ℓ + ℓ -, ℓ=e,μ very low σ Low mass M H ≲ 200 GeV H → γγ and H → ZZ* → 4ℓ are the only channels with a very good mass resolution ~1% Intermediate mass (200 GeV ≲ M H ≲ 700 GeV) High mass (M H ≳ 700 GeV) inclusive H → WW inclusive H → ZZ VBF qqH → ZZ → ℓℓνν VBF qqH → WW → ℓν jj M. pieri

Examples Low M H < 140 GeV/c 2 Medium 130<M H <500 GeV/c 2 High M H > ~500 GeV/c 2

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

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

SM Higgs: Cross section ~3fb (Khoze et al) MSSM: s ~ x10 larger (tan  ) Diffractive Higgs Production 100 fb 1fb Kaidalov et al., hep-ph/  H gap -jet p p Exclusive production:  J z =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  M = O( ) GeV 120 Also H  WW*

Invisible Higgs Decays LHC has the potential to see invisible Higgs decays Non SM Higgs e..g in SUSY

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

Mass and Width Resolution MSSM Higgs  m/m (%) 300 fb -1 h, A, H  0.1  0.4 H   0.4 H/A   h  bb 1  2  hh  bb  1-2  Zh  bb 1  2 H/A   1-10 Analysis of indirect widths for mass range below 200 GeV: 10-20% precision 5-8% 0.1-1% ATLAS PTDR

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

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 Higgs rest frame

Heavy MSSM Higgs Search At low tan , we may exploit the sparticle decay modes:  A, H   2 0  2 0  4l + E T miss  A, H in cascade decays of sparticles MSSM  5 Higgses: h,H,A,H  Contours for 5  discovery M H MAX scenario New: includes VBF channels A/H   A/H   A/H  bb/  in bb H/A H    H   tb

CP Violating Scenario  CP eigenstates h, A, H mix to mass eigenstates H 1, H 2, H 3  maximise effect  CPX scenario (Carena et al., Phys.Lett B (2000)) arg(A t )=arg(A b )=arg(M gluino )=90 0 Small area remains uncovered Could be covered by M H1 < 70 GeV (not studied yet) Significant dependence on the top mass (now 172.7±2.9 GeV) M. Schumacher

bbH,A → bbττ for M H ≲ 400 GeV –ττ → ℓ νν ℓ νν –ττ → ℓ νν had ν Higher mass also add –ττ → had ν had ν b-tagging, τ id and missing E t bbH,A → bb ττ From the cross section measurement it is possible to measure the value tanβ

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

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

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

Higgs Branching Ratios  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 Tim Barklow, LCWS04

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

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

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

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 Branching ratio can be determined with good precision: Better than 5% for large enough branching ratios Sum of width Recoil

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 

Top-Higgs Yukawa coupling The top-Higgs Yukawa coupling is very large (g ttH ~ 0.7 while g bbH ~ 0.02). Precise measurements important since could could show largest deviations to new physics Needs TeV collider and large luminosity If m H <2m t  e+e-  ttH If m H >2m t  measure BR(H  tt)

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

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

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 m H ~ 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 m H >   discovery ~1 year ~3 years Summary: Higgs at the LHC and LC

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 m H > 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 m H >200 GeV

ILC Higgs Summary The Higgs cannot escape the ILC, if within its kinematical range The Higgs mass can be measured down to 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