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Physics at the ILC
Ariane Frey, MPI München
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Physics at the ILC

• Higgs Physics
• Beyond the Standard Model
• Supersymmetry
• Extra Dimensions
• Heavy Z, Strong EWSB
• Precision Physics (top, W, )
• top, W

Ariane Frey, MPI München
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Success of the Standard Model

• Experimental discovery of all of its matter
  constituents and force carriers
• Simple common approach to describe all
  (relevant) forces gauge principle
• Self-consistent at the level of quantum
  corrections

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However. many open questions
Origin of mass ? ? Higgs
Unification of all forces ? SUSY ??
SM describes only a tiny fraction of our universe
what is the dark matter ?
Are quarks and leptons really elementary
particles ? Why q(e) - q(p) ? Origin of
matter-antimatter asymmetry in the universe ?
(CP violation) What about Gravity? Do hidden
extra dimensions exist ?
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Terascale Physics

• Why is the TeV scale interesting?
• SM without Higgs violates unitarity (in WLWL?
  WLWL) at 1.3 TeV!
  (something must happen!)
• Evidence for light Higgs
• What protects the Higgs mass at the TeV scale
• 2 Mtop 350 GeV
• Dark Matter consistent with
  
  
  
  
  (sub) TeV-scale WIMP
  (e.g. SUSY-LSP)
• SUSY Sparticles lt 1 TeV, many models lt 200 GeV

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Why an ee- Collider ?
All of this so far could have been a speech to
build the LHC !

• Difficult to reach high energies
  
  
  
  
  
  (synchrotron radiation)
• e pointlike particleknown and tunable vs of
  IS particles, polarization of IS particles
  possible, kinematic contraints can be used
• e electroweakly interactinglow SM
  backgrounds,no trigger needed,detector design
  driven by precision

• Easier to reach high energies
• p composite particleunknown vs of IS
  partons,no polarization of IS partons,parasitic
  collisions
• p strongly interactinghuge SM
  backgrounds,highly selective trigger
  needed,radiation hard detectors needed

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Hadron vs. Electron Collider
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Why an ee- Collider ?

• Electron positron colliders allow for
• Discovery of the unexpected
• Precision measurements of new old physics

telescopic
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Why an ee- Collider ?

• Electron positron colliders allow for
• Discovery of the unexpected
• Precision measurements of new old physics

telescopic
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Higgs discovery potential at LHC
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Higgs discovery potential at LHC

• Guaranteed SM-like Higgs discovery over the full
  allowed mass range with 30 fb-1 in one experiment
• Light Higgs most challenging
• Whole mass range could be excluded _at_ 95 CL
  after 1 month of running

• First measurements of Higgs properties possible
• Mass 0.1 0.4
• Production rates 10-20
• Ratios of couplings W/Z, W/t, W/t 10-20
• model-independent measurements of absolute
  couplings impossible

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Higgs - Task of a Linear Collider

• After the discovery of a Higgs boson, the key
  task of ILC is to
• establish the Higgs mechanism in all elements
• as being responsible for EW symmetry breaking
• Precision Measurements must comprise
• Mass
• Total Width
• Quantum numbers JPC (Spin 0, CP-even?)
• Higgs-Fermion couplings ( mass ?)
• Higgs-Gauge-Boson couplings (W/Z masses)
• Higgs self coupling (spontaneous symmetry
  breaking)
• Measurements should be precise enough to
  distinguish between
• different models (e.g. SM/MSSM, effects from
  extra-dimensions, )
• Aim at model-independence!

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Higgs Production
Dominant production processes at LC
Higgs-strahlung
WW fusion
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Higgs-strahlung ee -gt HZ Z -gt l l
H -gt qq
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Model-independent observation
Anchor of LC Higgs physics

• select di-lepton events
• consistent with Z?ee/µµ
• calculate recoil mass

model independent, decay-mode independent measurem
ent!
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Model-independent observation
efficiency is independent of decay mode
works over the whole rangeof possible Higgs
masses
precision on ?(HZ) 1-3 for mHlt200 GeV 3-20
for mHlt500 GeV
small differences can be correctedwith MC
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Measurement of the Higgs Mass
Model-independent HZ analysis only uses a
fraction of the events (Z?ll) For a precise mass
determination further statistics can be gained if
hadronic Z-decays are used. For mass
measurement, explicit Higgs final states (e.g.
H?bb) may be used Highest sensitivity to Higgs
mass comes from purely hadronic events Kinematic
fits improve the mass resolution
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Higgs Mass
sub-permille precision
500 fb-1 _at_ ?s 350 GeV
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Total Width
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Total Width
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Total Width
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Total Width Precision
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Higgs Quantum Numbers
Is it a Higgs boson ? Rise of cross section
near threshold is sensitive to Higgs Spin
for J0 rise ? for Jgt0 rise ?k ,kgt1 (some
cases for J2 are also ? but can be
distinguished from J0 through angular
distributions) also observation of H??? or
???H rule out J1 and require C
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Quantum Numbers
Method CP from transverse polarization
correlations in H?tt
Needs exclusive reconstruction t??? and t?a1?
decay modes
First estimate with detector simulation
gt 8? separation between CP and CP- for 120 GeV
Higgs (350GeV/1 ab-1)
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Higgs Branching Ratios
Higgs Branching ratios best to study Higgs Yukawa
couplings for a light H Crucial test ?(H?ff)
mf ?
At ILC measurement of gtabsolutelt BRs is
possible, because of decay-modeindependent gHZZ
measurement
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Higgs Branching Ratios
Most challenging disentangle the hadronic Higgs
decays H?bb H?cc H?gg
H?bb 68.2
H?cc 3.0
H?gg 6.7
for mH120 GeV
Need sophisticated flavour tagging Vertex
reconstruction using ZVTOP algorithm
(SLD) Tracks interpreted as 3D probability
tubes Vertices overlapping
tubes After vertex reconstruction, use ANNs
with vertextrack informationto obtain b- and
c-likeness for each jet
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Higgs Branching Ratios
?BR/BR bb 2.4 cc 8.3 gg 5.5 tt 6.0 gg 23
.0 WW 5.4
For 500 fb-1 MH 120 GeV
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Higgs Self Coupling
Higgs self-coupling (the holy grail) ?
essential test of the mechanism of
spontaneous symmetry breaking
V ?v2H2 ?vH3 1/4?H4 SM gHHH 6?v, fixed by
MH
6 jet final states !
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Measurement of Higgs self coupling
Tiny cross section Complicated multi-jet final
state ? detector design energy flow
Difficult backgrounds
jet mass resolution
60/vE
30/vE
Need highest luminosity Precision for 1 ab-1
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Higgs Profile
Use precision to check whether it is the SM Higgs
or signs of new physics beyong the SM
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Higgs - Global Fits

Interpretation of branching ratio and
cross
section measurements in global fits (HFITTER)
-level accuracy sensitivity beyond SM
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Excellent detector resolution helps !
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SUperSYmmetry
...now we have doubled the particle spectrum...
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Supersymmetry

• ... BUT solves several SM problems
• Link to gravity
• lightest SUSY particle stable
• ? Dark matter candidate
• Solves fine tuning problems
• Predicts light Higgs
• Unification of forces

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SUSY Higgs Bosons
In MSSM two complex Higgs doublet fields
needed (cancellation of triangle
anomalies) Minimal possibility two doublets
(weak isospin 1) ? 5 physical Higgs bosons
h,H neutral, CP-even A neutral, CP-odd H charged
Masses at tree-level predicted as function of mA
and tan? but large rad. corrections (top,
stop) mh lt 135 GeV
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SUSY Higgs at LHC
To prove the structure of the Higgs sector, the
heavier Higgs bosonshave to be observed either
directly or through loop-effects. Direct
observation difficult in part of parameter space
at LHC
Whats possible at a Linear Collider?
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SUSY Higgs Production at ILC
Production processes
Most challenging decoupling limit sin2(?-?) ?
1, mA large h becomes SM like H/A/H heavy and
mass degenerate
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SUSY Higgs Bosons
Very clear signal in HA ? bbbb 100 1000 MeV
mass precision due to kinematic fit drawback
pair production ? mass reach ?s / 2
Example for mH250 GeV / mA300 GeV at ?s 800
GeV
Reach extended into the LHC wedge region
?M/M 0.1-0.5 with 500 fb-1
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Typical SUSY spectrum
well measurable at LHC
precise spectroscopy at LC
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Supersymmetry - Task of LC
different SUSY breaking mechanisms yield
different spectra
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Supersymmetry - Task of the LC

• After discovery, the task is to reveal the
  underlying theory of SUSY
• breaking. The LC can do this by precision
  measurements of the
• masses and properties of the accessible part of
  the spectrum
• is it really SUSY?
• how is it realized? (particle content) MSSM,
  NMSSM,
• how is it broken? measure as many of the gt100
  parameters as possible measure them as
  precisely as possible -gt extrapolation to high
  scale
• Note successfully fitting the parameters of a
  constrained model
• to the observations is a necessary but
  not a sufficient test of
• the model.

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SUSY Production at ILC
This will be fun

• cross sections in the
• 10 1000 fb range
• o(103 105) events
• to disentangle this chaos
• the various LC options,
• in particular
• tunable ?s
• tunable beam polarisation
• are vital!

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Example Charginos
Sparticle Mass precision
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Example Sleptons
Pair-production
Examples
E
E-
Simple two-body kinematics and beam-constraint
allow for mass measurement of both slepton and
lightest neutralino
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SUSY - Dark Matter
If SUSY LSP responsible for Cold Dark Matter,
need acceleratorsto show that its properties are
consistent with CMB data - Future precision on
?h2 2 (Planck) match this precision! - WMAP
points to certain difficult regions in parameter
space
small
e.g. smuon pair production at 1TeVonly two very
soft muons! need to fight backgrounds
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LSP Dark matter candidate
Need to measure LSP mass, composition and
couplings !!
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SUSY cross checks
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Symmetry of SUSY
Selectron Couplings
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With a little help from my friends
Precise measurement at ILC
SUSY cascade decay at LHC
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SUSY Global Fit
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SUSY Global Fit
S-matter unification
Gaugino mass unification
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Extra Dimensions

• Completely alternative approach to solve
  hierarchy problemThere is no hierarchy
  problem
• Suppose the SM fields live in normal 31 dim.
  space
• Gravity lives in 4 d dimensions
• d extra dimensions are curled to a small volume
  (radius R)

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Extra Dimensions
Surface r2

• Density of
• field quanta 1 / r2

? Force 1 / r2
For massless quanta Coulombforce Gravity
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Extra Dimensions
cross section for anomalous single photon
production
Exclusion limits (95CL)
Discovery (5 s)
500 fb-1 _at_ 500 GeV, 1000 fb-1 _at_ 800 GeV
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Warped Extra Dimensions
gravity appears weak on SM brane (in ourworld)
due to exponentially warped metric in 5th
dimension
gravity at normal (SM-like) strength
SM brane
5th dimension ?
might observe spectacular KK-excitations of
the graviton graviscalar excitations
(Radions) which mix with the Higgs and
modify its couplings mass
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Extra Dimensions
Range of predictions for models with XD Effect on
each particle exactly the same size !
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Discovery through precision

• Precision measurements of SM processes are a
  
• telescope to higher scale physics
• Top quark
• Z and similar vector resonances
• Alternative EWSB
• etc.

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Top quark
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Top quark mass
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Where the top mass comes into play
predictions of EWparameters
Light Higgs mass prediction in SUSY
Prediction of DM density
?mH/?mt 1!
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Top Yukawa Coupling
- need highest energy - heaviest quark ?
surprises? - small cross section - complicated
final state
?g2ttH

• analysis in bb and WW decay
• huge and complicated backgrounds
• (ttWW is a 10-fermion final state)
• - b-tagging crucial to suppress bkg. and reduce
  combinatorial bkg.

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Top Yukawa Coupling
Result
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Top Yukawa Coupling
LHC is sensitive to top Yukawa coupling of light
Higgs through tth production. LC BR measurement
(h?bb and h?WW) turns therate measurement into
an absolute coupling measurement (LC can only do
it at high energy (gt 800 GeV))
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Giga Z running
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Improvement in EW parameters
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If no Higgs boson(s) found.

• divergent WL WL ? WL WL amplitude in SM at
• SM becomes inconsistent unless a new strong
  QCD-like interaction sets on
• no calculable theory until today in agreement
  with precision data
• Experimental consequences deviations in
  
• triple gauge couplings
  quartic gauge couplings

LC (800 GeV) sensitivity to energy scale
? triple gauge couplings 8 TeV quartic gauge
couplings 3 TeV ? complete threshold
region covered
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New Gauge Bosons (Z)
Heavy Z vector boson motivated by TeV scale
remnants of Grand Unified Theories, string
theories etc. Examples Z in SO10, E6 LHC
M(Z) up to 5 TeV ILC Unlikely to
directly produce a Z (Tevatron limits
approaching 1 TeV) virtual extension up
to 15 TeV measuring its interference with Z,?
exchange (PETRA could measure Z
properties without producing Zs)
5?
95CL
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New Gauge Bosons (Z)
If Z mass is known (e.g. from LHC) ILC can
measure the vector and axial-vector couplings an
pin down the nature of the Z
If here, related to origin of neutrino
masses If here, related to origin of Higgs If
here, Z comes from an extra dimension of space
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Whatever LHC will find,...

• ILC will have a lot to say!
• What depends on LHC findings
• If there is a light Higgs (consistent with
  prec.EW)
• ? verify the Higgs mechanism is at work in all
  elements
• 2. If there is a heavy Higgs (inconsistent with
  prec.EW)
• ? verify the Higgs mechanism is at work in all
  elements
• ? find out why prec. EW data are inconsistent
• 3. 1./2. new states (SUSY, XD, little H, Z, )
• ? precise spectroscopy of the new states
• No Higgs, no new states (inconsistent with
  prec.EW)
• ? find out why prec. EW data are inconsistent
• ? look for threshold effects of strong EWSB

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Summary

• A linear ee- collider with 500 -1000 GeV is on
  our wish list!
• Challenging machine and detector requirements,
  but no major obstacles.
• With ILC data can
• establish the Higgs mechanism
• complete the SUSY spectrum
• pin down LSP dark matter
• see signs of new physics way beyond the ILC (and
  LHC) energy through precision measurements
• look for exotic things (extra dimensions, Z,
  contact interactions)
• Best results when combining LHC and ILC
• LHC/ILC Study Group