1. ILC and future high energy physics
Yasuhiro Okada (KEK, Sokendai)
Mini-Workshop on Frontiers in Particle Physics Phenomenology
March 30, 2007, National Central University, Taiwan

2. Critical time for the high energy physics
LHC starts its operation this year. The first look at the TeV scale physics.
14 TeV pp collider starting spring 2008 at CERN.
Main targets of the LHC experiments are the Higgs boson and signals beyond the Standard Model.
Outcome of LHC will determine the future direction of high energy physics.

3. International Linear Collider (ILC)
The highest energy electron-positron collider.
The CM energy is up to 500 GeV in the 1st stage, and then aims to about 1 TeV in the 2nd stage.
High luminosity: 500 fb-1 for four years. ..
Accelerator R&D has been continued since more than 15 years ago. Accelerator technology choice was made in August Since then the machine design work has been lead by GDE (Global Design Effort)
~30km

4. RDR and DCR Two reports are in preparation.
Reference Design Report (RDR): Accelerator design report with the first cost estimate prepared by GDE.
Detector Concept Report (DCR): The first comprehensive report on physics and detectors at ILC prepared by “Worldwide Study of the Physics and Detectors for Future e+e- Linear Colliders”.
~100 pages for physics part and ~200 pages for detector part.
The final Draft will be released on April 1, 2007.
The current draft is available at the ILC wiki page.

5. Why TeV scale? : Higgs physics
SM Higgs mass constraints
in the LEP era.
TeV is the scale of weak interaction, i.e. the electroweak symmetry breaking.
The Higgs boson is probably light.
What is dynamics behind the Higgs mechanism? SUSY, Little Higgs? Extra dimensions? There should be a new interaction.
TESLA TDR

6. Why TeV scale?: Dark matter
About one fourth of the energy of the universe is carried by dark matter.
This indicate existence of a new stable particle.
If thermal production is assumed, the scale of the dark matter particle is likely to be near the TeV scale.

7. Why TeV scale?: Unification
Three gauge coupling constants are consistent with SUSY GUT.
If SUSY exists, this leads to a unified picture of particle physics and cosmology, which could include seesaw neutrino, leptogenesis, inflation and superstring unification.
Coupling unification in SUSY GUT

8. Why do we need both LHC & ILC?
Two machines have different characters.
Advantage of lepton colliders:
　　e+ and e- are elementary particle　
　　　　(well-defined kinematics).
　　Less background than LHC experiments.
　　Beam polarization, energy scan.
　　g - g, e- g, e- e- options, Z pole option.
LHC
ILC

9. The more LHC finds, the more ILC is needed.
Discovery of a Higgs boson at LHC.
Is this really Higgs particle?
Is the Higgs boson the SM one? If not, are there new phenomena besides the Higgs boson?
Discovery of a new gauge boson at LHC.
What are the properties of new force, and its meanings in unification and cosmology?
Discovery of SUSY particles at LHC.
Is this really SUSY?
GUT? SUSY breaking? SUSY dark matter?

10. Higgs physics
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.

11. Higgs boson search at LHC
SM Higgs boson branching ratio
Higgs boson discovery at LHC

12. Higgs study at ILC Precise determination of mass .
Spin and CP property.
Coupling determination.

13. Top Yukawa coupling Higgs self-coupling
C.Castanier,P.Gay,L.Lutz,J.Orloff
A.Gay

14. Proof of the mass generation mechanism of elementary particles
LHC: (10)% for ratios of
coupling constants
ILC: a few % determination
GLC project
mH=120 GeV, Ecm= GeV.L=500fb-1 (Ecm>700 GeV for Htt )

15. 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
SUSY correction to Yukawa couplings
B(h->WW)/B(h->tt)
B(h->bb)/B(h->tt) LC
LHC LC
ACFA report
J.Guasch, W.Hollik,S.Penaranda

16. 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

17. SUSY Higgs search In the MSSM, there are five Higgs states.
In the most of parameter space, the lightest one is a SM-like Higgs boson with mass less than 14 GeV.
Other four states are nearly degenerate with a suppressed coupling to gauge bosons.

18. g g H/A Laser e- beam a few mm Heavy Higgs search at ILC
Heavy Higgs bosons are pair-produced
at the e+e- collider mode.
If the gg option is used the mass reach
can be extended up to 80 % of e-e- energy. g
H/A
Laser
e- beam
a few mm g
GLC project

19. Direct searches for New Physics
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.

20. SUSY studies at ILC SUSY is a symmetry between fermions and bosons.
Spin determination is essential, ideal for ILC.
W,Z,g, H
gluon
lepton
quark
neutralino,
chargino
gluino
slepton
squark
SM particles
Super partners
Spin 1/2
Spin 0
Spin 1
neutralino mixing
chargino mixing
Mixing angle determination

21. Precision SUSY particle measurements at the ILC.
Determination of SUSY breaking and GUT scenarios.
Mass and mixing determination of chargino, neutralino, slepton, squark.
Chargino threshold scan
Smuon decay spectrum
~50 MeV
~100 MeV
H.U.Martyn

22. Extrapolation of gaugino and scalar mass parameters to the GUT scale with inputs from combined analysis of LHC and ILC.
Blair, Porod, Zerwas

23. Alternative Scenarios to SUSY
Determination of
the number of extra dim
at ILC 500 and 800 GeV
Main motivation for alternative scenarios
is to explain the stability of the weak scale.
Alternative scenarios involve new strong
dynamics or change of space-time, and
new signals at the TeV scale.
Large extra dimensions
Warped extra dimensions
Universal extra dimensions
Little Higgs models…
If LHC find the first signal of new physics
ILC will study new particles and interactions
and identify the underlying theory.
G.W. Wilson

24. Z’ coupling in various models Even if the initial ILC energy is not
enough to produce a new particle,
indirect effects can provide important
information for new physics.
Z’ mass =1,2,3,4 TeV e+ e- Z’ f
Ecm=500 GeV, L=1/ab
Godfrey, Kalyniak, Reuter

25. Connection to Cosmology
Many new physics models contain dark matter candidates from various reasons.
LSP in SUSY
LKP in Universal Extra Dimension model
LTP in Little Higgs model with T-parity
If the dark matter particle is produced as decay products of new colored particles, missing transverse energy signal is likely found at the LHC experiment.
ILC can distinguish different scenarios and determine dark matter particle’s properties to match the observed dark matter density in the universe.
Identification of the dark matter particle.

26. Cosmological parameter determination WMAP, Planck, …
Dark matter profile
in our galaxy
Thermal history
of the Universe
Cosmological parameter
determination
WMAP, Planck, …
Direct and indirect
(g, e+,anti-p, n ) searches
for dark matter
Thermal relic abundance
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/

27. SUSY Dark Matter
Ellis,Olive,Santos, Spanos
J.Feng
Dark matter relic abundance calculated from ILC results,
Bulk
Focus
Stau co-annihilation
A-pole
E.A.Baltz, M.Battaglia,M.E.Peskin,and T.Wizansky

28. Top Quark Physics Top quark mass and width
Top quark anomalous interactions
Top Yulawa coupling and anomalous
coupling to gauge bosons
Precision of the mass ~ MeV
Width measurement is unique at ILC.
A.H.Hoang
P.Bhartra and T,Tait

29. Coupling of Gauge Bosons
Coupling among gauge bosons
These measurements become very important for unexpected Higgs case.
Example: WW g anomalous coupling W g

30. Indirect sensitivity to Z’ boson at GizaZ
Very precise measurements at Z pole (GigaZ option) could provide an indirect sensitivity up to ~10 TeV though Z-Z’ mixing effects with improved masses of the top quark and the Higgs boson.
FLC: 500GeVILC + GigaZ
F.Richard

31. Conclusions
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.