Higgs Studies at the LHC and the ILC

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Higgs Studies at the LHC and the ILC
Albert De Roeck CERN SUSY 2005 18-23 July
Durham
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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)
• MHgt114.1 GeV _at_95 CL
• MSSM neutral Higgs bosons (LEP)
• Mh, MAgt92.9, 93.3 GeV _at_95 CL
• MH gt89.6 GeV _at_95 CL for BR(MH ? t?) 1
• MH gt78.6 GeV _at_95 CL for any BR
• Electroweak fits to all high Q2 measurements
  give
• MH9852-36 GeV (old top mass)
• MHlt186 GeV _at_ 95 CL (yesterdays new top mass)
• Tevatron searches ? see C. Tullys talk

Probably the most wanted particle in HEP Discover
or prove that it does not exist
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High Energy Frontier in HEP

• Next projects on the
  HEP roadmap
• Large Hadron Collider LHC at CERN pp _at_ 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) ee- _at_ 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 _at_ 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
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Higgs Roadmap

• Discover the Higgs (in the range 114.4 GeV lt MH lt
  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
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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

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SM Higgs production
NLO Cross sections
M. Spira et al.
gg fusion
IVB fusion
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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 ? ll?? VBF qqH ? WW ? l?jj
inclusive H ? WW inclusive H ? ZZ
H ? ?? and H ? ZZ ? 4l are the only channels
with a very good mass resolution 1
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Examples
High MH gt 500 GeV/c2
Medium 130ltMHlt500 GeV/c2
Low MH lt 140 GeV/c2
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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
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Other Channels (H?bb)
S/B0.03
S/B0.3
30 fb-1
Not discovery channels but can be used to
confirm/measure couplings
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Diffractive Higgs Production
SM Higgs Cross section 3fb (Khoze et al) MSSM
s x10 larger (tan?)
h
100 fb

• Exclusive production
• ? Jz0 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
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Also H?WW
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Invisible Higgs Decays
Non SM Higgs e..g in SUSY
LHC has the potential to see invisible Higgs
decays
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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
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Mass and Width Resolution
ATLAS PTDR
5-8
0.1-1
MSSM Higgs Dm/m ()
300 fb-1 h, A, H ? gg
0.1-0.4 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 widths for mass range below
200 GeV 10-20 precision
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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
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Spin and CP-quantum Numbers H ? ZZ?4l
ATLAS 100 fb-1
? MHgt250 GeV distinguish between S0,1 and CP
even.odd ? MHlt250 GeV only see difference
between SM-Higgs and S0, CP-1 ? ?,? less
powerful
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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
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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 lt 70 GeV (not studied yet) Significant
dependence on the top mass (now 172.72.9 GeV)
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bbH,A ? bbtt

• bbH,A ? bbtt
• for MH ? 400 GeV
• tt ? l?? l??
• tt ? l?? had ?
• Higher mass also add
• tt ? had ? had ?
• b-tagging, t id and missing Et

• From the cross section measurement it is
  possible to measure the value tanß

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Higgs Studies at an ee- Linear Collider

• ? L gt 1034cm-2s-1 ? 80 electron polarization
• ? Energy flexibility between vs 90-500 GeV
• Future possibility of ??, e-e-, e
  polarization, Giga Z

Can detect the Higgs via the recoil to the Z
e.g. Desch Bataglia LCWS00
? Fully simulatedreconstructed HZ event ?
Backgrounds low ? Robust signal if ?(ee?Hx) 100
times lower, still observable
Observation of the Higgs independent of decay
modes
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Higgs Production at an ee- Linear Collider
Dominant production processes at ILC
ZH
H??
? ln(s)
Example ?s350 GeV mH 120 GeV
L 500 fb-1 (2-4 years) 90 K Higgs
events produced
? 1/s
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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?
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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

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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
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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
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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(ee-) ? Measurement of ??/?
to10-20 with 1 year of data
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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
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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??????
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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 mHlt2mt ? ee- ?ttH
• If mHgt2mt ? measure BR(H?tt)

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LHC?LC data Top Yukawa coupling
Dawson, Desch, Juste, Rainwater, Reina,
Schumacher, Wackeroth
Assume a light
Higgs lt 2mt Production processes LC ee- ?
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
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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 150ltMHlt200 GeV
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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

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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 mHgt 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 mHgt200 GeV

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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)
• LHCILC(500) combined data give the best
  top-yukawa coupling measurement