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ILCの物理
岡田安弘 (KEK)
ILC測定器学術創成会議
２００６年６月２８日 KEK
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Fundamental questions in
elementary particle physics
What are the elementary
constituents of matter?
 What are forces acting
between them?
 How has the Universe
begun and evolved?

d  1016 cm  E  103 GeV  1TeV
 T  1016 K  t  1012 sec
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How have we come to the Standard Model ?
gravity
general relativity
EM interaction
Electroweak
theory
Higgs mechanism
weak interaction
Fermi theory
strong interaction
nuclear force
1900
pion
quark
QCD
2000
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Why TeV scale?
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This is the scale of the weak interaction, in modern
language, the Higgs vacuum expectation value (~246
GeV).
We expect to find a Higgs boson and “New Physics”
associated to the electroweak symmetry breaking.
The answer to the question “what is the physics behind
the electroweak symmetry breaking?” is a crucial
branching point for the future of particle physics.
Supersymmetry vs.
Low cut-off theory (Little Higgs models, models with
large extra-dimension, etc.)
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Why do we expect physics beyond the
Standard Model?
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We do not know how the Higgs field arises.
There are evidences which require new particles and/or
new interactions.
Neutrino mass
Dark matter
Baryon-anti-baryon asymmetry of the Universe
Expectation of Unification.
GUT, Superstring
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100 GeV
TeV
1019 GeV
Superstiring
Gravity
SUSY
GUT
Dark Energy
EM Interaction
Weak Int.
Strong Int.
Standard
Model
Seesaw
Neutrino
Inflation
Higgs Physics
Dark Matter
Baryogenesis
Alternative scenarios
(Extra dim, Little Higgs model,etc)
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Why do we need both LHC & ILC?
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Two machines have different characters.
Advantage of lepton colliders:
e+ and e- are elementary particles
(well-defined kinematics).
Less background than LHC experiments.
Beam polarization, energy scan.
g - g, e- g, e- e- options, Z pole option.
LHC
ILC
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Goals of ILC physics
Higgs physics (Electroweak symmetry breaking
and mass generation mechanism of quarks,
leptons, and gauge bosons.)
 New physics signals
Direct search for new particles and interactions.
Indirect search for new physics effects
through the SM particle processes.
Capability of precise measurements of various
quantities is a key.
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[1] Higgs physics
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A Higgs boson will be discovered at LHC as long
as its properties (production/decay) is similar to
the SM Higgs boson.
In order to study the Higgs mechanism at work,
Higgs couplings to various particles have to be
measured precisely.
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Higgs boson search at LHC
SM Higgs boson branching ratio
Higgs boson discovery at LHC
5
MH(GeV)
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Higgs physics at ILC
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Production of 0(105)Higgs bosons.
Determination of spin and parity.
Precise mass determination .
Measurements of production corss
sections and branching fractions
TESLA TDR
Higgs boson couplings to other particles
Mass generation mechanism
GLC report
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Coupling measurements at ILC
(Ecm>700 GeV)
LHC: (10)% for ratios of
coupling constants
ILC: a few % determination
Higgs self-coupling
GLC Project
mH=120 GeV, Ecm=300-500 GeV.L=500fb-1
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New physics effects in Higgs boson couplings

In many new physics models, the Higgs sector is
extended and /or involves new interactions. The Higgs
boson coupling can have sizable deviation from the SM
prediction.
The heavy Higgs boson mass in the MSSM
B(h->WW)/B(h->tt)
SUSY correction to Yukawa couplings
B(h->bb)/B(h->tt)
LC
LHC
LC
ACFA report
J.Guasch, W.Hollik,S.Penaranda
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Radion-Higgs mixing in extra-dim model
The triple Higgs coupling in 2HDM
in the electroweak baryogenesis scenario
HEPAP report
Little Higgs model with T parity
S.Kanemura, Y. Okada, E.Senaha
Deviation to 5-10 % level can be
distinguished at ILC
C.-R.Chen, K.Tobe, C.-P. Yuan
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[2] Direct searches for New Physics
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Some type of new signals is expected around 1TeV
range, if New Physics is related to a solution of the
hierarchy problem. (SUSY, Large extra-dimension, etc )
The first signal of New Physics is likely to be obtained at
LHC. (ex. squarks up to 2.5 TeV at LHC)
ILC experiments are necessary to figure out what is New
Physics, by measuring spin, quantum numbers,
coupling constants of new particles, and finding lower
mass particles which may escape detection at LHC.
Beam polarization, energy scan, and well-defined initial
kinematics play important roles in ILC studies.
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SUSY studies at ILC
SUSY is a symmetry between fermions and bosons.
Spin determination is essential, ideal for ILC.
SM particles
Super partners
quark
Spin 1/2
Spin 0
lepton
squark
slepton
gluon
Spin 1
W,Z,g,
H
Spin 1
Spin 0
(q~ )
~
(l )
(g~ )
Spin 1/2
gluino
Spin 1/2
neutralino,
~)
(

chargino
neutralino mixing
chargino mixing
Mixing angle determination
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SUSY relation
SUSY predicts characteristic relations
among superpartner’s interactions.
Right-handed selectron production
M.M.Nojiri, K.Fujii, and T.Tsukamoto
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GUT relation
Gaugino mass relation
If we combine information from
LHC and LC, we can test whether
SUSY breaking masses satisfy
GUT and/or Unification conditions
Gauge coupling unification
Scalar mass relation
B.C.Allanach, et al in LHC/LC report
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Large extra-dimensions
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An alternative solution to the hierarchy
problem.
LC physics:
Size and numbers of extra-dimensions,
The spin 2 property of Kaluza-Klein
gravitons.
graviton
matter
Angular distribution -> Spin 2 exchange
N.Delerue, K.Fujii, N.Okada
G.W.Wilson
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[3] Dark matter and collider physics
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Energy composition of the
Universe
Dark energy 74%
Dark matter 22%
Baryon
4%
Dark matter candidate
WIMP （weakly interacting
massive particle)
a stable, neutral particle
WIMP candidates
Neutralino (SUSY)
KK-photon (UED)
Heavy photon (Little Higgs
with T parity)…
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Dark matter profile
in our galaxy
Thermal history
of the Universe
Cosmological parameter
determination
WMAP, Planck, …
Thermal relic abundance
Direct and indirect
(g, e+,anti-p, n ) searches
for dark matter
Detection rate
Collider search for a dark matter candidate
particle at LHC and ILC.
ILC will play a particularly important role in distinguishing different models
and determine properties of the dark matter candidate.
See, E.A.Baltz,M.Battaglia,M.E.Peskin,and T.Wizansky, hep-ph/0602187
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SUSY Dark matter at ILC
SUSY mass and coupling measurements
=> Identification of dark matter
ALCPG cosmology subgroup
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[4] Precision measurements of SM processes
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Improve precision of the fundamental parameters.
Search for new physics in indirect ways.
The threshold scan improves
the top mass measurement
and determines the top width.
Top quark threshold scan
Deviation of the top width in
the Little Higgs model.
C.F.Berger,M.Pelestein,F.Petriello
GLC report
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Z’ and e+e-->ff processes
Z’ coupling determination at ILC
Even if ILC at 500 GeV cannot produce
a new Z’ particle kinematically,we can
determine left-handed and right-handed
couplings from ee-> ff processes.
This will give important information
to identify the correct theory.
LHC=> mass
ILC => coupling
e
f
Z’
e
f
m z’ =2TeV,Ecm=500 GeV, L=1ab-1
with and w/o beam polarization
S.Godfrey, P.Kalyniak, A.Tomkins
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[5] Physics Benchmarks for the ILC Detectors
M.Battaglia, T.Barklow, M.E.Peskin, Y.Okada, S.Yamashita, and P.Zerwas, hep-ex/0603010
The big table
•Benchmark
processes for
detector design
and optimization.
•Selected from
important physics
reactions
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The short list
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Conclusions
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The LHC experiment is expected to open a new era of
the high energy physics by finding a Higgs boson and
other new particles.
Establishing the mass generation mechanism is the
urgent question. This will be achieved by precise
determination of the Higgs couplings, and ILC will play
essential roles.
In order to explore New Physics, Higgs coupling
measurements, direct study of new particles and new
phenomena, and indirect searches through SM
processes are all important at ILC.
TeV physics explored at LHC and ILC will lead to new
understanding of unification and cosmology.
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